That doesn't necessarily mean that devices using the adaptive USB mode will always have compromised performance. Stello's U2 USB-S/PDIF converter, which I reviewed in May 2010 ($349), and Centrance's DACPort D/A headphone amplifier, which I reviewed in June 2010 ($399.95), both offer excellent performance despite operating in adaptive mode. But in December I reviewed the Halide Design S/PDIF Bridge USB-S/PDIF converter ($450), which operates in asynchronous mode, and was sufficiently convinced by its performance that it became my default recommendation for extracting audio data from a computer in order to feed those data to a legacy D/A converter (footnote 1).

The Halide S/PDIF Bridge was the first USB-to-S/PDIF converter of which I was aware that operates with high-resolution data in asynchronous mode, and that did not require that a driver program be installed on the host PC. But now there is another: the V-Link, from English company Musical Fidelity. Like the Halide, the V-Link handles 24-bit data with sample rates up to 96kHz, but it costs just $169. Okay, unlike the Halide, the V-Link needs to be used with an S/PDIF or TosLink cable and a USB link, which will add to the cost, but $169 is still one heck of a low price for something that offers the potential for true high-end sound quality from a computer.

The V-Link
The V-Link is encased in the same rectangular, black-painted aluminum extrusion used to house the other products in Musical Fidelity's inexpensive V series. On one end is the usual USB Type B jack; the other end sports an RCA jack, a TosLink optical port, and blue and green LEDs. The blue LED indicates when the V-Link is being powered by the USB bus; the green LED lights when the V-Link is being fed audio data.

Inside, a multilayer printed circuit board runs the full length and width of the enclosure. A three-pin voltage-regulator chip supplies 3.3V to the circuitry. The USB datastream is fed to a Texas Instruments TAS1020B receiver chip, which converts the audio data to two-channel i²S format. The TAS1020B includes an embedded microprocessor; the firmware that allows it to operate in asynchronous mode is stored in a socketed eight-pin chip. The i²S output from the TAS1020B is fed to a Burr-Brown DIT4096 chip, which converts the data to S/PDIF and can operate at sample rates up to 96kHz. A single crystal on the board is used as a high-precision, single-frequency oscillator to drive the TAS1020B processor clock and its internal frequency synthesizer; the latter generates both the 44.1 and 48kHz word-clock frequencies and their multiples.

The electrical output of the V-Link doesn't appear to be connected with a pulse transformer, which means that it's possible that the grounds of some DACs will not be galvanically isolated from that of the host computer. This, presumably, is why Musical Fidelity's Antony Michaelson recommended to me that I use the V-Link's TosLink output if possible.

Setup
Setup is as simple as plugging the V-Link into one of your computer's USB ports, connecting its S/PDIF output to a D/A processor with either a coaxial cable or a TosLink optical cable, and selecting the V-Link as the default audio output device in the computer's Control Panel. I hooked up the V-Link to the 2006 Mac mini that I use as a music server; the Mac's USB Prober utility revealed that the converter identified itself as "Musical Fidelity V-Link" from "Musical Fidelity" operating in asynchronous mode; the serial-number string was displayed as "0." The host computer ran iTunes and Pure Music in Memory Play mode. (Pure Music also takes care of adjusting the sample rate of the data output to the V-Link to match that of the file being played.) The dCS Debussy I have in-house for a Follow-Up to Michael Fremer's January 2011 review doesn't have an optical input, so I used the V-Link's coaxial output. The dCS successfully locked to the Musical Fidelity's output at all sample rates up to 96kHz.

Thanks to such an attitude among Quad and many others, audiophiles were left with cost-ineffective modified players, or kludges. Problem was, these tweaked players were expensive—lots of skilled labor involved—and mechanically, the basic machine was still crap.

I think Meridian and Marantz were the first to offer CD players of very high quality. Others came around—notably Denon (which still produces some of the best players on the planet), Yamaha, Pioneer, Onkyo, and NEC. (Remember NEC? They got out of the hi-fi business. Stuff was damned good. I digress . . .)

The Musical Fidelity Digilog sold for $995, if I remember rightly. At the time, many hi-fi customers didn't know what it was because the category was being created—by Antony, among others. I remember explaining what it did in my column in October 1989 (Vol.12 No.10). The Digilog helped kill off the kludgemeisters.

Many more DACs followed from Musical Fidelity. I still own the Tri-Vista 21 DAC from 2003 and occasionally fire it up. That one sold in the US for $2395.

The M1 DAC is by Musical Fidelity. At $699, it's a stunning bargain. Comparing it to $995 for the Digilog in 1989. Meanwhile, the M1 is far more versatile, way better built, and, if memory serves me right, sounds vastly better.

It appears that the way to sell a DAC in 2011 is to almost give it away, in real-dollar terms. Some people pay far more than this for a set of speaker cables, a pair of interconnects, even a power cord. The M1 DAC is a piece of kit that can transform your system. I kid you not.

At the moment, the M1 is the only DAC available from or by Musical Fidelity, aside from the even less expensive V-DAC for $299. But we're not counting accessories—the V-DAC comes in a blister pack. Get one before they're gone, for a second system.

"The M1's technical performance is, pretty well, as good as any at any price," writes Antony Michaelson in the product information sheet, which is long on words (like me) and short on specs.

"Pretty well"? That does seem to leave room for a future DAC from Musical Fidelity. If such a DAC does appear, you can safely assume it will cost far more than $699. Meanwhile, save your money and run with the M1.

I am not in a position to judge the M1's technical performance. What, me measure?

Antony continued: "The M1 DAC has vanishingly low distortion, typically less than 0.005% across the band. Frequency response is ruler flat. Jitter is extremely low. The noise ratio is outstanding, one of the quietest DACs in the world regardless of price." Whereupon he invited comparison with DACs up to ten times the M1's price. No one has sent me a $7000 DAC lately. Or a $1000 DAC, for that matter.

Compared to previous Musical Fidelity DACs, the M1 offers more input options: coax, TosLink optical, AES balanced, USB. It locks on to any S/PDIF signal at 32, 44.1 ("Red Book" CD), 48, 88, 96, or 192kHz. All incoming data rates are upsampled to 192kHz. But what about an incoming USB signal? Is that more limited in terms of incoming data rates? Antony was not available and, with the Christmas holiday fast approaching, I didn't find out (footnote 1).

Except in the very literal world of digital audio, which is crawling with silver bullets. First, consider that word-clock jitter is always musically destructive: There is no such thing as an acceptably musical digital source with high levels of jitter. Second is the fact that it's always easier to listen to a cached, solid-state digital file than one that's undergoing the messy process of being pulled from a CD like a rat from its hole. Third is . . . well, I'll get to the third one in a minute.

Digital terrier
If I owned such a number of CDs that my servants and I couldn't rip them all ourselves, I'd consider buying another CD player to replace my 12-year-old Sony SCD-777ES, which itself replaced a perfectly nice Naim CD3—a move of questionable wisdom, now that I think about it. But today, thanks to breakage, loss, and generosity, my CD collection is contracting, even as my vinyl and shellac collections expand. (The universe is expanding too, but not fast enough.)

Computer audio is not only the right choice for me: It's a happy choice. The genre is still fun—especially if you avoid upturning the rocks beneath which the Internet's computer-audio "experts," who belch condemnation at every approach that isn't their own, lie in wait. And it's still affordable: The audio perfectionist who already has a free copy of Apple's iTunes on his or her computer is able to get up and running for just a few hundred dollars, with USB-to-S/PDIF converters and USB digital-to-analog converters from HRT, Musical Fidelity, Stello, and a growing list of others. Computer audio is the road to freedom from obsolescence, extortionate prices, and those glorified kitchen-table manufacturers who thanked their best customers—the people who bought the first multi-thousand-dollar CD players of the late 1980s and early 1990s—by neglecting to stock enough spare parts to keep their overpriced goods running for more than five years. Throw in freedom from ugly, splintered, useless CD jewel cases and the matter is settled.

By the same token, there exist more expensive options that promise more than just CD-quality (footnote 1) sound. Consider the successful QB-9 USB D-to-A converter, which Ayre Acoustics introduced two years ago for the moderate sum of $2500. Ayre kindly loaned me a sample—and then, toward the end of last year, called it back for what I assumed would be improvements. Charles Hansen, Ayre's CEO, was quick to set me straight: "The new version doesn't sound any better. It just has an extra feature: It can go to 192kHz instead of just 96kHz." Fair enough. But because it might sound better when it does that, I asked to reborrow the same QB-9. (Hansen saw no reason to alter the model name: "We knew when we started it would have to change eventually.")

Ayre endeavors to make all their product upgrades retrofittable, and so it goes with the 192kHz version of the QB-9: The retail price was bumped to $2750, and people who invested in the early QB-9 can have theirs upgraded at the factory for the price difference alone: $250. Charles Hansen says he would've done it for less if he could have. "The part that would go to 192 was only a little more expensive, but then we had to add another board and change the power supply, too." The new chip—an XMOS XS-1 from Bristol, UK—is simply a microprocessor, and thus requires a separate receiver chip.

There remains a lack of controls on the Ayre's front panel, but the DIP switches on the back have taken on a new shine: One of them controls whether the QB-9 is connected at Class-1 USB or Class-2 USB data-transfer speed, the latter required for sampling frequencies higher than 96kHz. The choice is also determined by the owner's computer operating system: Although Class-2 USB capabilities have existed on Macs for a number of years, it wasn't until OS 10.6.4 that sample rates beyond 96kHz were supported. Windows users may require an extra driver, but Charles Hansen says that the prep work isn't daunting: "For Class-2 you do need to have your computer pretty current, but we spell it all out on our website."

Without asynchronous streaming, USB audio functions in adaptive mode: the computer establishes the data-transfer clock, forcing any outboard digital-to-analog converter or other such device to adapt to that rate. Worse still, adaptive mode asks the converter to derive a clock signal from a USB operating frequency that's mathematically unrelated to any digital audio frequencies known to man. It's like putting a driver behind the wheel of a car whose speedometer is calibrated in miles per hour and telling him to maintain a steady speed of exactly 70.13 kilometers per hour, lest he go off the road and die, unpleasantly: Accident avoidance requires one to perform a continual series of high-speed calculations on the fly.

Alternatively, Rankin's Streamlength software, which resides in a ROM chip within the USB device, empowers the converter to do something that USB converters don't normally do: provide its own clock, rather than live or die by the clock in the incoming datastream. Rankin says that this reduces jitter by a significant margin; his success in licensing Streamlength to such manufacturers as Ayre Acoustics, Berkeley Audio, Halide Design, and others might be taken as a sign that it works.

Description
Like other Wavelength Audio products, the Proton contains an almost fanciful amalgam of old and new technologies: a glorious mosaic, shrunk and made electric. Tiny surface-mount resistors and capacitors share space with old-style carbon-comp resistors and ice cube–sized Mundorf M-Caps, which in turn share space with a ROM chip, a TAS1020B USB receiver chip with embedded microprocessor, voltage regulators, and a 3.6V rechargeable lithium-ion battery. (History buffs, take note: Lithium-ion batteries were invented in nearby Binghamton, New York, which is also home to McIntosh Laboratories.) There's even a sprinkling of Åber-rare Black Gate capacitors in there—the red ones!

At the center of all this, figuratively and nearly literally, is a Wolfson XWM8721 DAC chip that also incorporates an analog volume control and a headphone amplifier. Within an inch of the Wolfson DAC are two low-jitter oscillators, which generate the signals for both sample-rate families: 22.5792MHz for 44.1 and 88.2kHz, and 24.576MHz for 48 and 96kHz. Four LEDs on the Proton's rear panel correspond with those four sampling rates: visual confirmation that you're hearing what you hope you're hearing.

In an effort to eliminate the hated wall wart—Rankin wanted his least expensive DAC to be usable while traveling, as well as at home—the Proton's basic functions are powered by the 5V that appears on the USB port, while the critical analog side of the Wolfson DAC chip is powered by the above-mentioned lithium-ion battery, which is recharged while the computer rests between tasks—or, in the case of some contemporary machines, even when the computer is powered down. Rankin estimates 25 to 30 hours of playback time per charge; when the battery dips below a certain voltage, the Proton goes into charge mode, which is indicated whenever two rear-panel LEDs of the same sample-rate family are illuminated. (When two unrelated LEDs light up—say, 44.1 and 48kHz—that indicates a hardware failure.) Interestingly, during this product's development, Rankin discovered that the precise value of its power-supply voltage regulator is sonically critical: The 3.6V regulator he initially chose let through too much computer noise. By switching to a 3.3V regulator, Rankin was able to reduce the Proton's jitter level considerably.

All of the above is built into an aluminum extrusion more or less the size of the average moving-coil step-up transformer. Internal build quality was superb, and the review sample looked very nice indeed. In particular, the Proton's rear panel, with its engraved lettering and its neat row of LEDs, had a purposeful look that complemented both my iMac rig and my hi-fi.

Setup and installation
The Wavelength Proton was darn near plug-and-play: Unpacking the review sample, plugging a cable from my iMac's USB bus into the Proton's USB type B socket, and connecting the latter's RCA line-output jacks to the inputs of my Shindo preamp took all of four minutes. (Those RCA jacks are sufficiently close together that the use of very thick cables, or cables equipped with Koala-style battery packs, is mildly challenging but not impossible.) After that, I selected System Preferences from my iMac's screen dock, clicked on Sound, then on Output, and, when "Proton USBDAC" automatically appeared, selected that: another 90 seconds of arduous, grinding labor.

I suppose I could have stopped there, but a couple of essential tweaks remained: First, with the Sound window still open on my iMac, I clicked on Sound Effects, and then, from the pull-down menu halfway down the window, I selected Internal Speakers instead of Proton USBDAC. I've found this to make a notable improvement in the quality of computer-music sound, although I don't know the technical explanation why.

Second, the Proton contains its own analog volume control, which is adjusted from the associated computer. But the last 10% of its range is intended only for headphones—to use that additional range on the line output is to risk clipping the signal. (I'm not a headphone kinda guy—sorry—so the vast majority of my listening was done with the Proton's line outputs driving my music system.) If you're running iTunes on a Mac, the solution is easy: When using the Proton as a line-out device, open the Audio MIDI Setup utility and knock the volume for both channels down to 91%. For playback software (such as Decibel) that bypasses the MIDI utility, or for Windows or Linux machines, use the volume control in the menu bar to approximate 90%.

Combined, those tasks required a little less time than it takes to microwave a serving of Tandoor Chef brand Palak Paneer. Which is excellent, by the way.

The Proton's instruction sheet says that a brand-new unit requires both a battery charge and a period of break-in before sounding its best, and suggests that the best way to do the latter is through normal (as opposed to continuous) use. Done.

But if you discover a ding in the door of one of them, where most folks still see only a new car, you now see the ding. It might have been there all along, undetected the first few times you walked around the car—maybe your buddy even had to point it out to you. It's insignificant in the scheme of all that a new car is, but once you've seen it, you always see it. Now you can easily tell the two cars apart, and we both know which one you'll drive home.

I've got a neighbor who owns an auto-body shop and prides himself on pristine body work and the perfect paint job. I'll never forget the time he took a walk around my spankin' new car and pointed out a half dozen almost imperceptible dents and blemishes in the finish. I'd had the car a month and never seen a thing, but he knew how to look at a finish. You can bet that, after that, I could easily pick out those blems.

Same thing with DACs. That small difference may be hard to hear, but once you have, it can make all the difference. And the more DACs you listen to, the better you get at noticing these details.

Whenever I plug in a new DAC, it sounds pretty much like the last DAC I had in my system. But if I work at it enough, and spend enough time walking my ears around its sound, I can usually figure out how it differs from the others—not always, but it happens more often than not. And I'll wager that, with a little effort, you can, too. Some differences are so slight it takes a while to spot them, while others slap you in the face. But once you've heard them, you can hear them every time. Maybe I'm an audio masochist, but I like testing DACs and seeing if I can spot the dings.

At the 2011 Consumer Electronics Show, in Las Vegas, I came across the Peachtree iDac and was immediately drawn to its complete assortment of digital inputs (including an iPod dock), good looks, and price: $999. But CES is no place to critically listen to something like a DAC; Stephen Mejias arranged for a review sample to be sent, so I could hear where it might place sonically among the dozen or so DACs I've had in my system this past year.

Features Front to Back and On Top
With their uniquely rounded casework, solid and hefty feel, high quality of fit, and glossy finishes, Peachtree Audio components are easy to spot, and the iDac is no exception—it's so lovely, rounded, and inviting that I can imagine using it as an audiophile pillow. Have you seen those wooden headrests the ancient Egyptians used to sleep on, or the ones Japanese geishas use to keep their hairdos intact? The iDac looks way more comfortable, and it would keep your ears warm. But not too warm—the iDac ran at a comfortable 94°F all day long (I took its temperature at the top of its case); by comparison, my Benchmark DAC1 USB easily hits 105°F, even in idle. Everyone who saw the iDac in our system had to touch it. A few even stroked it with the back of a hand.

On the clean-looking, silver front panel is a row of six flat, round input buttons; slightly below and to the left and right of these are, respectively, the power button and remote sensor. Simple enough, but the lighting scheme used for these demonstrates Peachtree's attention to detail. The power button is surrounded by a ring that glows red for off, blue for on. Select an input and it, too, turns blue. But if no digital signal is present, or the iDac can't lock to the input chosen, the blue keeps circling the button like a lighthouse, until you plug something in and power it up. Nice little touch. However, I wish I could have dimmed those blue lights—in a small bedroom, they're bright enough to serve as nightlights—though the red standby light is fairly subdued. There is no volume control or headphone jack.

The included remote control is simple, and also controls an iPod inserted in the iDac's dock. The dock, on the top of the case, comes with several plastic inserts, to adapt its connector to those of most iPod models. It takes the direct digital signal from the iPod, bypassing Apple's mediocre internal DAC. Setup was dead simple, everything worked as advertised, and the dock is canted back at just the right angle to make it easy to read an iPod from above when the iDac is positioned at around waist height.

On the iDac's rear panel are one pair of fixed-level stereo line outputs, component and S-video outputs (for iPod video), and pairs of optical USB and coaxial digital inputs. In addition are two pushbutton switches: Hi-Bit/Lo-Bit and Filter NOS/NAL. NOS stands for "no filtering or oversampling," NAL for "nonaliasing."

According to Peachtree's David Solomon, most audiophiles "don't generally like steep filter slopes because they don't sound very good. This means that our DAC (and any DAC that uses a gentle filter slope) is more susceptible to filtering aliasing distortion." To solve this problem, Peachtree uses upsampling. "Sample rates of 96kHz or 192kHz help to attenuate aliasing but doesn't entirely get rid of it. So Peachtree Audio developed software that eliminates aliasing distortion in the sampling process."

About Hi-Bit/Lo-Bit: The ESS 9016 Sabre chip used in the iDac is an eight-channel DAC. Each channel comprises an array of 64 individual switching elements, and there are two ways to run the Sabre in two-channel mode. In Lo-Bit mode, the two-channel signal is replicated four times and fed to the eight channels, their outputs paralleled to yield the two-channel result. In Hi-Bit mode, the switching elements of the Sabre's eight channels are rearranged to form two channels with 256 elements each, to accept signals of higher resolution.

After playing with these options a while, I decided I preferred NOS—it sounded slightly smoother, though Peachtree says NAL measures better—and left the iDac set to NOS for all of my listening. Playing with the Hi-Bit/Lo-Bit switch was interesting: Hi-Bit moved voices forward and opened the soundstage a tad, and Lo-Bit sent them back. I ended up using Hi-Bit for most of my listening, but Lo-Bit when I wanted more control. I find it fascinating that you can use these sorts of settings to fine-tune things like soundstaging and presence.

Next to Kalt on the couch, his girlfriend, Maryann, was nodding her head up and down to the music. At the loud level Kalt had set, the staccato start/stop style of "Jambi" had taken control of the room. He turned to me, remote in hand, and tilted his head toward the volume setting, as if to ask "Can I turn it up?" I nodded, and we all proceeded to bounce (yes, the floor and couch were bouncing a little) to the onslaught as Tool's glory pinned our ears back even tighter.

"Jeff and I bonded to the music of Tool," Maryann confided to me later. Two such sweet, almost shy people—I never would have guessed. Under their unassuming surface were an intensity of purpose and an intelligence that, I would come to discover, are also present in Kalt's products.

When I get a new product in hand I normally shun its manufacturer's advances, preferring to experience my first impressions of the product just as a regular buyer would. But when Kalt pointed out that his dealers often offer a setup service for new customers, I relented. Turns out the Cantata was easy to set up and use, but I discovered that this attention to the customer was, indeed, pretty standard for Resolution Audio. Take the box the Cantata comes in: a sturdy, handmade, stamped wooden crate carefully lined with foam that perfectly cradles the product.

Senses Working Overtime
Audio products are here to stimulate our sense of hearing, but the Cantata also pulls sight and touch into the mix. Jeff Kalt says he worked closely with his metal fabricator to get the most unique casework I've seen enclosing an audio product: the top is an undulating sea of scalloped aluminum waves. It must be seen to be believed, and touched to be understood. Stunning. The Cantata is also fully packed; at 13 lbs, it weighs more than its looks suggest, and that top panel got a bit warm (about 102°F).

For those who, like me, have left analog sources behind, the Cantata may be all that's needed in addition to amplification (a matching Cantata 50 amplifier is available) and speakers. The Cantata is a digital preamp with a built-in CD player, and a DAC for everything else digital. And I mean everything.

On the front right half of the low-slung Cantata's front panel is an array of small holes; splashed across the 1"-thick edge of the aluminum top, these holes hide a retro- yet oddly futuristic-looking large alpha-numeric display. Below the aluminum slab is a row of buttons on a black background. From left to right, these are power, input select, volume up/down, the disc-player controls, and the built-in CD player's all-but-invisible disc drawer. Clean and to the point.

More comprehensive control is available via either the Cantata's medium-size remote control or, with a free app, your iPad, iPhone, or iPod Touch. The beautifully designed app controls all of the Cantata's functions, and Kalt has created the best implementation of touchscreen volume control I've seen. Instead of the typical slider bar, which can accidentally be pushed to full window-shattering volume with a single errant tap (trust me, I've done it), the Cantata app has a calibrated virtual wheel that spins forward and back as you swipe at it. Elegant and idiot-proof.

On the Cantata's rear panel are, from left to right: the power switch, fuse, and detachable grounded power-cord socket; a Cantata Link (for hooking up to RA's Cantata amps); Ethernet, USB, TosLink, AES/EBU, and coax inputs; and balanced and unbalanced stereo outputs. Unlike the Ethernet jacks found on most components these days, this one is not only for controlling the Cantata via your network, it's also a digital audio input (as I'll explain shortly).

Swiss Army DAC
I set out to test as many methods of running digital audio through the Cantata as possible. These included using the CD slot on the front; the S/PDIF, TosLink, and USB inputs on the back; and from my Apple computer, via the rear-panel Ethernet jack, connecting to Resolution Audio's Cantata Pont Neuf Bridge USB adapter (see below), and to a wireless WiFi bridge (also via the Cantata's Ethernet jack and the Pont Neuf).

Nightmares of lo-rez audio iClouds got you down? Create your own local full-resolution audio cloud. Most folks will integrate a computer as a source component into their system via USB, and while regular USB DACs require a computer in the listening room due to the 1–2m limit on the length of USB cables for best performance, Resolution has come up with a way to create a wireless "bridge" between a computer or USB music source in another room and your system, like a Sonos system on steroids.

This last option is one of the Cantata's more interesting features: using a wireless bridge and a remote computer, you can wirelessly stream, via WiFi, audio of resolutions up to 24-bit/96kHz. To make this work, Jeff Kalt created the Pont Neuf USB to Ethernet Bridge ($400). (Pont Neuf, French for "new bridge," is also the name of one of the Paris bridges spanning the Seine.) It looks like a mini Cantata—it, too, has a top plate of scalloped aluminum—and is the size of a pack of chewing gum. At one end of the USB-powered Pont Neuf is a USB plug for inserting into your computer and, at the other end, an Ethernet jack.

To test this type of connection, I ran the USB output of my Mac to the Pont Neuf, which I then connected to my WiFi network locally with an Ethernet cable. I then connected the Cantata, in the listening room in another part of the house, via its Ethernet jack to an Apple Airport Express. I controlled the remote computer's music libraries with my iPad. The Cantata wasn't connected to the network directly via Ethernet, only through the Airport Express. After I'd configured the AE to join my WiFi network and restarted it, setup was simple, and within minutes I was streaming from both iTunes and the VLC player (for FLAC files) at any sampling rate up to 96kHz. And it sounded great.

In fact, I tried dozens of cuts, and couldn't hear a reliable difference between using a wireless bridge via Ethernet and the Pont Neuf, and direct S/PDIF or the Cantata's disc player. I was prejudiced to hear some flaws with the WiFi-Ethernet connection, but could never hear any. Same thing after adding USB to the mix. This surprised me quite a bit.

Macca On the Mac
During this review, I received CD copies of the new Abbey Road remasterings of Paul McCartney's McCartney and McCartney II); then HDtracks.com made available downloads of the 24/96 FLAC versions. These two releases are confusing in that McCartney II was released 10 years and many Paul McCartney and Wings albums after McCartney. Something to do with how each was recorded as one-man solo effort in a small studio, and the albums in between were full-on studio/band affairs.

Fact is, the predominant digital source at audio shows is now a computer, and Stereophile has been covering the components required to extract audio data from computers for some time now (footnote 1). My beat has been to review products intended to transform a USB feed into the AES/EBU or S/PDIF serial datastream needed to drive a traditional outboard D/A converter. The subject of this review, Empirical Audio's Off-Ramp 4, does the same thing, but at prices that range from $799 for the basic model to $3068 for a fully tricked-out version with outboard battery supply, it's significantly more expensive than the similar products I've reviewed in the past. My review sample included the Dual Turboclock ($700) option, to which I added the Monolith lithium-ion battery supply ($1199), for a total price of $2698.

This review was long in gestation because the Off-Ramp 4 proved somewhat of a moving target. I returned the sample three times to Empirical for upgrading before I could crystallize my findings, and as I finished up the review, I found out that an upgrade of the voltage regulators, a $300 option, had just been introduced. Empirical's Steve Nugent explained in an e-mail that, "As in most of my products, there are modules that I upgrade over time. My products are not just as-is. They are moving targets, getting constant improvement which can make them a bit difficult to review at times. The customers however love this because they are not buying into obsolescence. Especially important for Computer Audio, which is constantly evolving. They know that down the road when new technologies and improvements come along, they can upgrade and don't have to sell their older gear and shop for something new."

Technology
The Off-Ramp 4 is a small box: a rectangular-section, black-anodized aluminum extrusion with black endcaps. The front has three status LEDs; the rear has a USB port, an XLR jack for the AES/EBU output, an RCA jack for the S/PDIF output, an RJ-45 jack for the I²S output (footnote 2) and a DC input jack. Unlike other USB converters, which are USB 1.1–compliant and are thus limited to 24-bit/96kHz audio data, the Off-Ramp 4 conforms to the faster USB 2.0 specification and can handle 24/192 datastreams. However, a driver program is required for each operating system used by the host computer, which Empirical supplies on a CD-R. (These can also be downloaded from Empirical's website.)

Inside the Off-Ramp 4, a motherboard runs the full width and depth of the enclosure. The USB port is connected to a daughterboard populated with surface-mount components on its upper and lower sides. The USB receiver on this board uses, under license, programmed parts from Italian company M2Tech that, Steve Nugent says, are similar to those used in the M2Tech hi-Face USB bridge. These are a programmable USB interface chip from Cypress Semiconductor (a CY7C68013A, which includes an onboard microcontroller), and a programmed flash memory and programmed Xilinx FPGA for the clock division and buffering. An AKM AK4114 chip checks the signal integrity and lights the amber data-error LED if non-PCM data are detected. A red LED lights if no USB data are present. A green LED indicates that valid PCM data are present at the USB input.

As can be seen in the photo of the Off-Ramp's innards, two shielded clock links are taken to this board from the master clock circuit, which resides on another daughterboard. The review sample's Dual Turboclock option uses a high-precision crystal oscillator for each of the two sample-rate families: 44.1, 88.2, and 176.4kHz; and 48, 96, and 192kHz. All sample rates are generated by dividing the frequency of these two clocks, and each oscillator circuit is powered from its own discrete voltage regulator with heatsink..

The output of the USB receiver board appears to be taken to a second AK4114 chip, which provides the S/PDIF, AES/EBU, and I²S outputs. Steve Nugent ranks the sound quality potential of the data outputs as I²S, then S/PDIF, then AES/EBU. The overall parts and construction qualities are high; I spotted at least one premium Black Gate electrolytic capacitor.

Power is taken from a DC jack on the rear panel with a positive-center 2.5mm pin. The circuits are protected from reverse voltage. A 12VDC wall-wart power supply is provided, but a sophisticated outboard battery supply, the Monolith, is also available. The Monolith can be used with Empirical Audio's Pace-Car and Overdrive DAC products as well as the Off-Ramp, and has three pairs of lithium-ion cells and the necessary charging and management circuitry. A Neutrik five-pin high-current connector on the Monolith's rear panel supplies 12V and a ground return. The Monolith is powered from the same wall wart supplied with the Off-Ramp; a toggle switch on the Monolith's front panel selects off/charge or AC power on, with a momentary position selecting battery operation.

The Monolith will not operate without a source of power, but when the batteries are fully charged, the AC adapter is disconnected from the output. When the batteries are discharged to the point where they might start to affect the sound quality, the Monolith automatically and transparently switches the AC adapter back to the output, disconnects the LI batteries, and begins charging them.

Sound Quality
Setup was as easy as installing the correct driver for my operating system—my 2006 G4 Mac mini runs OS X 10.5 (Leopard), the final version compatible with its obsolete G4 processor—connecting the Off-Ramp 4 to one of the computer's USB ports, and connecting its AES/EBU output to a D/A processor. (I don't like RCA-connected S/PDIF outputs and the review sample didn't have the optional 75 ohm BNC connector.)

Prior to auditioning the Off-Ramp 4, I'd been using the BNC version of the Halide Bridge USB-S/PDIF converter ($450, reviewed in December 2010), with the Logitech Transporter used as a D/A converter. With music served from my Mac mini running Pure Music, I felt I had reached a plateau in the quality of my system's source: an easy sound that wasn't too laid-back, with a wide, deep soundstage, and a full presentation of recorded detail that wasn't thrust in my face. Then, in place of the Halide, I hooked up the Empirical Audio Off-Ramp 4, powered from its wall-wart supply.

Now that was interesting. The soundstage got a little wider and deeper without becoming unstable. Individual objects within that soundstage, such as the treble recorder, oboe, trumpet, and violin in J.S. Bach's Brandenburg Concerto 2, with Richard Egarr directing the Academy of Ancient Music (24/88.2 download, Harmonia Mundi HMU 807461.62), got a little smaller but were actually slightly better focused.

I went back to the Halide, and the stage both shrank a little and lost a very slight degree of image focus. I returned to the Off-Ramp 4 and heard the same improvement I had before. I then powered the Off-Ramp 4 from the Monolith battery supply: the differences I'd heard between the Halide and Off-Ramp became more intense. Despite the complex interplay between the voices at the start of the Dunedin Consort's performance of Bach's St. Matthew Passion (24/88.2 Studio Master download, Linn CKD 313P), each voice retained its own space within the soundstage.

Footnote 2: The I²S bus is a proprietary digital-audio-data interconnection standard intended by its progenitor, Philips, to be used inside a CD player or digital control center. As it runs a separate connection for the data clock signal, it is less prone to introducing jitter into the recovered clock than the S/PDIF and AES/EBU data protocols, in which the clock is embedded in and needs to be extracted from the data.

Dear Erick:
I really want to get into computer audio, but the economy sucks and most of the stuff you review in Stereophile seems way overpriced. Is there anything that will play my audio files and CDs that won't send me further into debt?—Sue P. Cichen

Dear Ms. Cichen:
Yes, there is. In fact, I think we're entering new age of great-sounding, inexpensive digital-to-analog converters (DACs) that can do a lot for relatively little money. For instance, I recently spent some time with the CEntrance DACmini CX, which accepts S/PDIF, TosLink, USB, and analog inputs, and costs a very reasonable $795. You can buy the DACmini CX directly from CEntrance's own website.

The DACmini CX comes in a standard, silver-finished aluminum chassis that's designed to share the same footprint as Apple's original Mac mini. (Get it? Mac mini? DACmini?) The faceplate of the DACmini has knobs for selecting the input and setting the volume level, and a ¼" headphone jack that's driven by a class-A–biased headphone amplifier with no capacitors in its signal path.

The DACmini CX is also galvanically isolated: Signals cross the analog/digital divide via a sophisticated magnetic barrier without ever making actual electrical connection. The RCA connectors are isolated from the chassis with plastic washers, to avoid ground contact. Computers are notorious for creating grounding problems when hooked up to audio systems; galvanically isolating the DACmini's analog section means there's far less chance of creating grounding noise in your headphones or speakers.

The DACmini CX is powered by an external switching supply much like one you'd use for a laptop computer, and it has a typical IEC receptacle—you can use a fancy aftermarket AC cord, as I did. The line-level signal leaves the DACmini via a single pair of gold-plated RCA jacks.

The DAC chip in the DACmini (an AKM 4396) accepts signals with word lengths up to 24 bits and sample rates of up to 192kHz via the CEntrance's coaxial input, and up to 96kHz via USB. I think you'd agree, Ms. Cichen, that the DACmini CX offers a lot of features for a reasonable sum.

Erick:
It seems that lots of DACs these days have volume controls. I want to sell my preamp and plug a DAC straight into my amps. Any suggestions?—Noah Middlemann

I'm with you, Mr. Middlemann. I am a big fan of DACs that can also control a system's volume. The result is a much more direct signal path that lets folks save money they otherwise might spend on a costly preamp and extra cables. Companies are starting to figure out that customers want this kind of configuration and simplicity.

I was pleasantly surprised that, a few months after the release of the DACmini CX, CEntrance began offering modifications for it. Each mod costs $99.95; CEntrance will build your DACmini CX to order, or trick it out for you later. The available mods are: a black-anodized finish; Headphone Linearity, which lowers the headphone impedance from 10 ohms to 1 ohm for use with low-impedance headphones: Rock and Roll, which increases the gain for the headphone output (useful for high-impedance 'phones or listeners who want to go deaf); and Variable Output, which uses the DACmini's headphone volume control to adjust the level of the signal from the rear-panel RCA jacks.

Once the DACmini CX was available with Variable Output, I asked for a review sample. I found it very easy to hook up to my power amps and use it as a DAC, headphone amp, and preamp. Unlike some other DACs with volume controls, the DACmini attenuates volume in the analog domain.

Dear Mr. Lichte:
I wish Stereophile would stop covering computer audio. USB audio is stupid. So are you.
Eat my shorts.—Bea Ligerant

Dear Ms. Ligerant:
While I sympathize with your assessment of me, USB audio is not as bad as it used to be. CEntrance seems to understand the inherent pitfalls, and have made their own set of choices about how to handle them in their DACmini CX.

As most folks know, the big problem with using USB for audio is the timing errors it introduces in the streamed data. The USB format was never designed to provide a continuous stream of uninterrupted data. Instead, USB sends out data in packets. This hardly makes a difference when you click your mouse to tell your printer to print something, but it makes a big difference for digital audio, which requires perfect timing between source (a computer) and DAC. When timing errors result from this miscommunication, jitter-related spuriae appear in the reconstructed signal.

If audio data are accepted by the DAC whenever the computer's bus wants to send it, this is called a synchronous connection. Left untreated, such connections are typically not very good—the computer will send data only when it has a moment when it's free from the myriad other operations it's constantly handling.

One way to combat jitter in a USB connection is to have the DAC and the computer shake hands before they begin exchanging data. In this secret handshake, the DAC is given permission to continuously monitor the computer's data-transfer rate, then adapts its own clock, on the fly, to match it. This is known as an adaptive isochronous USB connection.

In an increasingly popular way to use USB for audio, an asynchronous connection, the DAC's clock takes charge of the computer and tries to guarantee that the computer sends it data only at the rate the DAC needs. The DAC clock can therefore be of high precision, hence low jitter.

In the DACmini CX, CEntrance uses yet another way to minimize jitter via USB. As Michael Goodman, CEntrance's chief product architect, told me recently, "Any engineer skilled in digital and analog design knows that jitter is inevitable in digital communications. It results from the fact that computers always send data in irregular chunks, since they are doing several things at once. The crux of audiophile D/A conversion is how well you clean up the audio samples prior to their presentation to the DAC. Our products reduce jitter to well below audible levels. We employ a proprietary two-stage jitter-reduction algorithm, called JitterGuard." Essentially, JitterGuard is a buffer that sits between the USB receiver and the DAC chip. CEntrance's premise is that as long as the DAC chip sees buffered data that are correctly clocked, it doesn't make much difference if the USB connection is adaptive, synchronous, or asynchronous.

As always, Ms. Ligerant, the proof of any audio philosophy is in the listening. I hope this helps you hate USB, and me, a little less.

Dear Erick:
I want to use my computer as an audio source, but I hear that USB audio is really difficult to set up properly. I'm scared.
Trepidatiously—Freda Njüthing

There, there, Ms. Njüthing. I'm here for you. Many companies now make USB-based audio products that can achieve bit transparency without you needing a computer-science degree or having to constantly adjust your Mac or PC. In my opinion, the state of USB audio is vastly different from what it was just two years ago—it is now easier to accurately transfer audio data.

For instance, CEntrance's DACmini CX is able to work with any computer without the user having to install a driver program. You just plug it in and play. CEntrance also offers a free, downloadable, ASIO driver/control panel for Windows users. I listened to the DACmini with and without the ASIO driver and preferred the sound with it. I also liked the peace of mind of knowing that I was bypassing as much of Windows Vista's audio processing as I possibly could.

Erick Lichte:
I believe that computers are the Mark of the Beast. I don't want to EVER have a computer involved in my audio hobby. All I want is a nice DAC–preamp–headphone amplifier that will make my old CD player sound better.
Peace—Sev N. Tseel

Mr. Tseel:
I understand. I have a love/hate relationship with my laptop. Though I like some of the musical convenience of listening through it and I love the sound of high-resolution digital, I don't fancy having my computer as part of my listening experience.

I still believe that DACs need to play "Red Book" CDs well to be a viable part of my audio system. I recently hooked up the DACmini CX to my Bel Canto CD2 CD player, to get a sense of what the CEntrance sounded like when I played normal CDs like a normal audiophile. Listening to Four Tet's DJ-Kicks (CD, !K7 203), I was struck by the rather tubey and analog quality that the DACmini brought to the music. The DACmini gave the music on this album a full-sounding midbass, a generous midrange, and a treble that was delicately balanced but ever so slightly smeared. Transients didn't quite have the startling snap that I often hear through other DACs, but what the DACmini lacked in speed it made up for with a pleasing, almost decadent tonal balance. Listening to the DACmini, I would have thought it was some sort of tubed source component, not some under-$1000 digital player with a switch-mode power supply.

I decided to play to the DACmini CX's strengths by listening to the Latvian Radio Choir singing Peteris Vasks' imploring Dona Nobis Pacem, for choir and organ (CD, Bis CD-1145). The DACmini presented a generous picture of this music; the choir sounded rich and full, while the varied registrations of the organ came through with clarity. The choir's sibilants were beautifully balanced in level with the rest of the singing. But again, I heard a slight treble smear that made s sound a tad like sh. However, the treble also had a sense of delicacy and shimmer that made the DACmini's slightly smeared treble less of a problem.

In terms of soundstage, the DACmini CX threw a large one, especially in terms of width. Again, the CEntrance focused on the music's organic qualities. It tended to connect instruments and voices in a pleasing way, in a way it often does in concert, instead of concerning itself with the spatial dissection of instrumental images. In other words, the DACmini revealed the musical forest and let the individual trees take care of themselves. My only real complaint with this approach is that front-to-back layering of the soundstage was not as engaging as I've heard from the similarly priced Benchmark DAC1 or the more expensive Bel Canto DAC 3.5VB. I found the DACmini CX to be one of the more musical DACs in its price range, but not the most revealing.

Shlain believes that the very way people thought was transformed by the alphabet's demands to break concepts down and express them reductively, linearly, and abstractly, rather than perceive them concretely and holistically through images. Shlain claims that the alphabet's success caused the brain's abstraction- and linear-oriented left hemisphere (which is also the seat of speech) to dominate the right hemisphere, which is oriented to intuition and images. He claims that the alphabet's dominance led to what he calls the "inventions" of imageless gods, written codes of law, patriarchy, misogyny, and intolerance. (The opposites being gods that can be represented by images or sculptures, unwritten customs and traditions, gender equality or matriarchy, and tolerance.)

Of course, such broad-brush ideas can't be proved or disproved, but Shlain is not afraid to bite off huge swaths of cultural history and chew them rather thoroughly. I hasten to point out that Shlain—who, after all, writes books—is not anti-literacy. He merely offers his observation that elevating book literacy to the most revered—and, in some cases, exclusive (footnote 1)—way of perceiving and representing reality had immense consequences at the outset that continue to resonate today. Shlain believes that the invention of the alphabet (as distinct from the invention of writing, say, hieroglyphics) is second only to the development of speech in making humans and society what they are today.

The relevance I find to music is this. As I write this, I have no idea what peoples' reactions will be to my avowal, in the November issue's "As We See It," that Beethoven's music at times strikes me as repetitive, excessively rhetorical, or argumentatively dialectical. I expect that quite a few readers will be upset, and quite a few may be condescending or perhaps even pitying. But it just came to me, as I was listening to some Debussy, that perhaps what I sometimes find uncongenial about Beethoven is that his music can be not only stereotypically "masculine," but also "left-brain,""linear," and "reductive." Not all of Beethoven's music, of course; the slow movement of the Violin Concerto, the slow movements of the piano sonatas, and the slow movements of the string quartets are full of priceless moments of quiet beauty. On the other hand, Beethoven's position in the pantheon of Western classical music is somewhat analogous to that of the Old Testament deity.

Beethoven's most famous musical motto is, of course, the opening of his Symphony 5: Da-da-da-daaah. Isn't that a bit like someone who thinks he has something important to say to you jabbing his forefinger into your chest? And isn't what follows at least somewhat abstract, linear, and analytical?

My point is not to make people have heart attacks or froth at the mouth. I am trying to grope my way to an explanation of my statement in November that "Mahler is the new Beethoven." Aided by Shlain's book, I might be getting a glimmering that "Mahler is the new Beethoven" because Mahler's music is not so stereotypically masculine left-brain, linear, and reductive.

Think for a moment about the nebulous, numinous quality of the opening of Mahler's Symphony 1. Can anything be further from the opening of Beethoven's Fifth? I'm not prepared to say that Maher's music is more "feminine," but I do think it is plausible to claim that Mahler's music is concrete and holistic, and that it is not rhetorical or argumentative—and so perhaps Mahler's music better fits our times. Trivia bit: The opening section of Alexander Courage's theme music to the original Star Trek TV series—the numinous bit before the rhythm section literally begins the beguine—borrows from Mahler's Symphonies 1 and 7.

I'd appreciate anyone else's thoughts on why "Mahler is the new Beethoven." The e-mail address is at the end of the column.

Grace Design m903 D/A Headphone Amplifier
I have long been a fan of Grace Design's headphone amplifiers. In fact, I have long been a fan of Grace Design. Like many of the pioneering companies of the hi-fi era (Klipsch, McIntosh, Marantz, and Fisher, to name a few), Grace is the result of a single person's conviction. Michael Grace was working for the Jeff Rowland Design Group, and wanted to design a microphone preamplifier that was as good as the stuff Rowland was building. Rowland was unwilling to expand into the pro audio field, so Grace departed to pursue his dream.

After getting his microphone preamplifiers well established (users include Skywalker Sound and the band Phish), Grace built a one-off headphone amplifier for a customer. Friends who heard it wanted their own, so he made 50 of them. Those soon vanished, and the rest is history. You don't have to look too hard to see that Grace Design's products have some of the same design aesthetic as Rowland's, even though Grace's products are not quite the same level of "audio jewelry."

It's a bit hard to believe that Grace's first headphone amplifier, the model 901, debuted 10 years ago (my coverage of it ran in Stereophile's March 2003 issue). Two years later, in June 2005, I wrote about the 901's replacement, the m902, which added a new DAC capable of handling 192kHz inputs, unbalanced analog outputs, a blue LED numerical display, a crossfeed circuit for headphone listening, and a USB 1.0 input. The m902 used the same transimpedance amplifier circuit as the 901, however. It's fair to sum up my reaction to the m902 as "Same great sound, more features." I think that, for many listeners, the most important new features were the line-level analog outputs, which allowed the m902 to function as a DAC and preamplifier.

Back in 2005 I paid little attention to USB connectivity, for two reasons. First were my own listening experiences, which were overall not very positive. Indeed, Wes Phillips found the m902's sound via its USB connection to be "murky." The second reason was professional snobbery: none of my colleagues who were professional recording engineers used USB to record. Such snobbery was not groundless: USB 1.0 is bandwidth-limited. Furthermore, when professional musicians are playing or singing their hearts out, you don't want your recording rig hiccupping because some arcane internal function decides it's high time to make sure that its internal date and time are exactly what the mother church in Cupertino, California, says they should be. So, back then, many engineers used only digital-audio computer interfaces (such as RME's Hammerfall) that tie directly into the computer's system bus via the PMCIA slot or via a FireWire link. Today, with the advent of USB 2.0 (and lots of lessons learned), the situation is different. One of the most respected digital interfaces is Sadie's LRX2, which uses USB 2.0 to store 16 channels of 24-bit/96kHz PCM on a Windows laptop, and is the preferred location-recording rig of Peter McGrath.

Grace has now replaced the m902 with the m903, which, unlike the m902, is pretty much new from stem to stern (except for its industrial design and ergonomics). New are the m903's DAC, USB module, transimpedance amplifier circuit, and volume control. The power supply, balanced current-to-voltage converter, headphone crossfeed, and s-Lock PLL digital lock all are improved. The m903 comes standard with balanced analog outputs, although to save rear-panel space these are on ¼" TRS phone jacks rather than XLR jacks. (Balanced outputs were first offered late in the m902's production, as an extra-cost option.) The numeric display is now white rather than blue. Despite all these improvements, the m903 remains reasonably priced at $1895. (Infrared remote control remains an extra-cost option.)

Building a Fire
The Weiss DAC202 has not only two FireWire ports, but also AES/EBU, S/PDIF RCA, and TosLink connections. A BNC input and output allow it to lock on to an external clock. There are also ouputs for AES/EBU and RCA S/PDIF digital signals. The narrow front panel has a largish LCD screen and a single knob, which you spin or depress to access and control any of the DAC202's menus and functions. The infrared remote control can be used to access the most frequently used functions: Power, Volume, input (FireWire, XLR, RCA, TosLink), Mute, Phase, and Filter, for the two onboard digital filters (more about those later). I found the dimmable screen very intuitive and easy to use to access every feature of the DAC202, and the remote is simple and elegant in design and feel. Also on the front panel are a ¼" headphone jack, an IR sensor, and a power-status LED. The fit and finish are good; the front panel's beveled edges look quite nice, and the knob had a sturdy yet silky feel. Still, the DAC202's looks favor function over opulence.

The DAC202's power supply uses a toroidal transformer and there are separate voltage regulators for the analog and digital supplies, a total of 11 regulators. The circuit board is laid out for optimal current distribution. The DAC202 uses the premium ESS9018 DAC chip, which allows for two digital filters (here labeled A and B) to be used. According to designer Daniel Weiss, filter A is optimized for an ideal stopband corner frequency, while filter B has a relaxed transition band that gives the optimum transient response. Jitter is suppressed with what Weiss calls a Jitter Elimination Technologies Phase Locked Loop (JET PLL), which uses feedback to lock the local oscillator to the incoming timing reference. In the DAC202, the JET PLL has two loops. One has its corner frequency set low enough to give good jitter attenuation. The corner frequency of the other loop, which regulates the analog oscillator, is set much higher. The DAC202 uses two converters per channel to increase its signal/noise ratio by 3dB, and it can accept data resolutions up to 24-bit/192kHz.

While so many other consumer DACs now connect with computers via USB, the Weiss DAC202 uses FireWire, which is favored in professional audio circles and fundamentally differs from USB in a number of ways. First, FireWire has greater bandwidth than USB and can therefore transfer more data faster. Second, FireWire is a peer-to-peer protocol, which means that every device on a FireWire network is equally capable of talking to every other device. Third, FireWire is always implemented in hardware, with a special controller chip in each device; the communications load it puts on your computer's CPU is much lighter than USB's.

According to Daniel Weiss, FireWire is more reliable than USB because it offers what he calls "isochronous mode, and it lets a device carve out a certain dedicated amount of bandwidth that other devices can't touch. It gets a certain number of time slices each second as its own. The advantages for audio should be obvious: that stream of data can just keep on flowing, and as long as there isn't more bandwidth demand than the wire can handle (not very likely), nothing will interfere with it. With our products, the FireWire connection works in the so-called isochronous mode, which means that a defined bandwidth is reserved for the link and cannot be taken by another device on the bus. To use USBspeak, the transfer is asynchronous; ie, the master clock sits in the D/A converter and the computer is slaved to it."

The DAC202's volume control is an analog/digital hybrid. Via a menu on the LCD screen, four coarse volume steps in the DAC202 are implemented in the analog domain. Once a range is set, controlling the volume, using either the knob or the remote, is done in the digital domain. This lets the user run the digital volume at the top of its range, where its effect on the signal's word length is minimal. Weiss also applies noise-shaped dithering to the 24-bit volume control to maintain maximum transparency.

Setting Fire
Setting up the DAC202 was a breeze—especially connecting it to my computer. Using an off-the-shelf FireWire cable, I hooked up my Sony Vaio Laptop (an Intel Core duo processor running at 2.4GHz with 4GB of RAM) to the DAC202, then ripped files from Weiss's supplied test disc, which contains data files of various sample rates and bit depths. I selected the Bit Transparency Test from the DAC202's menus, then played the test files from my laptop via J. River Media Center. The Weiss is the first computer-based audio product that could easily and unambiguously tell me that my computer was outputting a truly bit-transparent signal at all bit depths and sample rates. This level of onboard diagnostics should be mandatory for all DACs intended to be used with computers. Bravo, Weiss!

I used a Bel Canto Design e.One CD2 as a disc transport and connected the DAC202 directly to my power amps (Rogue M180 monoblocks or a Plinius SA-103) via the Weiss's balanced outputs. Before taking any serious listening notes, I let the DAC202 burn in for a few hundred hours.

Dance into the Fire
Describing the sound of the Weiss DAC202 is one of the easier tasks I've had to do for Stereophile. The DAC202 made music with delicacy and liquidity; its tonal balance was extremely natural, with a forgiving top octave; and it presented music with an easy grace that digital music rarely has. No matter what connection I used, which amp was in the system, or whether I was listening to high-resolution computer files or CDs, the DAC202 always retained these fundamental sonic traits. The Weiss was in no way concerned with dissecting music into its atomic elements, but instead projected its gestalt onto everything it played.

Classical music benefited from the DAC202's easy, liquid character. Latvian composer Eriks Ešenvalds's A Drop in the Ocean, from Polyphony and the Britten Sinfonia's Passion and Resurrection (CD, Hyperion CDA67796), was conveyed with musical generosity and an expansive soundstage. The DAC202 was kind to choirs, heightening their blend and offering remarkable tonal balance, with clear, unhighlighted sibilants and no trace of hardness. Via the DAC202, no part of the tonal spectrum was ever given undue prominence

I used the Polyphony disc to test the DAC202's filters. Filter A offered a bit more extension in the high treble (I was surprised I could hear this difference), and a little bit better stopping and starting of notes. However, Filter B offered a more three-dimensional quality, greater liquidity, and a smoother top end. I felt that Filter B played more to the DAC202's strengths, offering sound that even the most digiphobic audiophile could appreciate.

The DAC202 also did a great job with hi-rez files from my computer. A few months ago I became the proud owner of the Beatles' entire stereo catalog in 24-bit/44.1kHz, complete with a green metal apple in which to house the flash drive. The DAC202 brought out the greater palpability of these hi-rez files compared with their 16/44.1 counterparts. Compared to the "Red Book" CD remasters, the panned voices in the hi-rez version of "A Day in the Life," from Sgt. Pepper's Lonely Hearts Club Band (24/44.1 FLAC), sounded less like images of voices moving through space and more like entire singing bodies moving from left to right through the stereo field.

Rega designs for simplicity and reliability. We do the fussing so that you don't have to, Terry Bateman told me—or words to that effect. It's the reason you can't fiddle much with a Rega tonearm. It's also the reason Rega turntables never break.

Roy Gandy told me about one Rega turntable that did break. It seems a bloke had a fight with his wife: he grabbed one side of the turntable, she the other. The 'umble 'table landed on the floor, its glass platter shattered, its plinth cracked. What, if anything, could be salvaged? I find it very British that the gent seemed at least as concerned about saving his turntable as his marriage. I forget the outcomes.

Rega has gone upmarket with a number of products, including two CD players, both named Isis: $8995 solid-state, $9995 tubed. That's right: tubed. Terry Bateman has always been keen on valves: "Just give me a pair of 6BQ5/EL84 tubes any day and I'll go away a happy bunny," he wrote in an e-mail. The Isis players are anything but 'umble eye-fye. When I heard that some of their technology had trickled down into the Rega DAC ($995), I gave Rega's US distributor, Steve Daniels, at The Sound Organisation, a bell, as the British like to say. Or a tinkle. I do love to piss people off.

Though the Rega DAC measures only 8.4" (215mm) wide by 3.1" (80mm) high by 10.5" (270mm) deep, there's a lot packed inside, Bateman says. There are two coaxial and two optical (TosLink) inputs—four S/PDIF inputs in all. (S/PDIF stands for Sony/Philips Digital Interconnect Format, aka Sony/Philips Digital Interface.) There's also one USB input for direct USB link to your computer. One oddity of the Rega DAC is its small IEC C5 mains input, chosen to save space. If you want to use an aftermarket power cord, your Rega dealer can supply an adapter; I didn't ask for one.

Bateman doesn't see USB "as a high-tier audio interface. . . . I came to this decision whilst researching professional studio-based outboard audio equipment, and nearly all the digital audio interfaces are AES/EBU (close relative of the S/PDIF format) and not USB."

In an earlier e-mail, Bateman had said something about USB's convenience and utility. I think he's spot on about that. I tried listening to Internet radio and my favorite podcasts from my computer, via USB, to the Rega DAC. I used my Musical Fidelity X-Cans^V8 headphone amp to drive my AKG 701 headphones and my powered Advent speakers from yesteryear (the small ones, same as the powered ARs).

When you connect to your computer USB-to-USB, the signal goes to the Rega DAC's Burr-Brown PCM2707 USB receiver—the same chip found in Musical Fidelity's M1 DAC. This receiver chip is why you're limited to data rates of 48kHz and below and 16 bits via USB; but not so via the four S/PDIF inputs.

If you want to send higher data rates from your computer to your DAC, you need a USB-to-S/PDIF converter, such as Musical Fidelity's V-Link ($169) or Halide Design's The S/PDIF Bridge ($450). You engage the Rega's five digital inputs via buttons on the front panel; that's where you'll also find buttons for the 10 digital filters (more about these below). My head is already spinning. Like a CD.

The Rega DAC's sound was distinctive and superb. I was extremely happy with the sound I was able to, er, wrest from my "medium-rez" CDs. I took my favorite discs—heh-heh—for a spin, using my Sony SCD-XA777ES SACD/CD player as a transport. For the most part, I listened with my LFD LE IV integrated amplifier driving my Triangle Comète Anniversaire speakers via LFD speaker cables. For direct comparisons, I connected the Musical Fidelity M1 DAC to the LFD integrated with the same ancient XLR interconnects.

The Rega DAC had a richness, a fullness of tone, an analog sense of ease, that I had not hitherto heard from digital, save for SACD. I heard a naturalness, an organic quality to the sound. The Rega DAC didn't sound at all busy with the bits. Superior resolution aside, the Rega DAC reminded me of my bedside Sony D25s Discman, from about 1989.

Older CD players can do that, sometimes: surprise me with their musicality, if not their ultimate resolution. Another such player from roughly the same era is my MicroMega Stage 6. Often, in hi-fi, we get technological progress but not sonic improvements. It's what drives Art Dudley, Ken Kessler, and others back to the past, and rightly so. Why did I sell my Spendor BC1 speakers?

There's never anything in heavy rotation chez nous, but I've been enjoying several CDs in particular. The Rega wrangled Rachmaninoff to the ground—his complete Preludes, performed by Alexis Weissenberg (CD, RCA 09026-60568-2-8). The weight of the notes from the left-hand side of the piano was remarkable—and this from my Triangle Comète Anniversaire speakers, which can't do deep bass. The beefy Bulgarian was in our living room.

I enjoyed that richness of tone: body, weight, authority. I also enjoyed a newer recording, this one nominated for a Grammy: Nelson Freire's set of Chopin's Nocturnes (2 CDs, Decca 001405302). Compared to the M1 DAC, the Rega DAC gave me greater richness of tone, a more relaxed sound. The M1 DAC, when I reverted to it, displayed distinctive virtues of its own: a certain lightness and fleetness of foot, more apparent air and openness in the top end. There seemed to be more space between the notes.

In its own way, each DAC was thoroughly convincing; listening to one, I did not terribly miss the other. But I was trying to hear differences, so of course I did. Scientific researchers call this Positive Expectation. Or Negative Expectation, as the case may be. You get the results you want.

This puts me in a pickle. There were times when the Rega's weight and bass authority stunned me and the M1 seemed lean by comparison: austere is probably the right word. It happened again last night, when I played Haydn's Symphony 103, "Drum Roll," with the Vienna Philharmonic conducted by Nikolaus Harnoncourt (3 CDs, Vienna Philharmonic 2009). The drum rolls practically rolled me out of my seat—and this was with the somewhat bass-shy, stand-mounted Triangles.

It is therefore good engineering practice to place the timing circuit, for obvious reasons referred to as a "clock," as close as possible to the D/A circuit. But a PC clock several feet away, at the other end of a USB cable, is clearly not "as close as possible." Worse, a computer must attend to other tasks, so its clock is inherently less stable than the crystal oscillator found in a DAC. The optimal solution is to allow the DAC to control the flow of USB data from the computer; this is what is meant by asynchronous.

Not all USB receiver chips can be operated in asynchronous mode, an exception being the Texas Instruments TAS1020B. This USB 1.1 device includes an onboard microcontroller that can be programmed to run the interface in asynchronous mode. Gordon Rankin of Wavelength wrote proprietary code for the TAS1020B's microcontroller; as well as using it in his own USB products, he licenses this Streamlength code to hardware manufacturers. One such is Halide Design, who used Streamlength in their S/PDIF Bridge converter ($395), which I reviewed in December 2010. The Bridge comprises a USB cable with a tubular housing at one end, terminated in either an RCA or a BNC jack. The Bridge operates in asynchronous mode to convert USB-streamed audio data to the S/PDIF serial format required by traditional D/A processors. Because there is no jitter-inducing S/PDIF cable—the Bridge connects directly to the processor's input jack—the Bridge became my preferred means of connecting a computer to DACs that lacked an asynchronous USB port.

It seemed an obvious development for Halide to marry the Bridge's asynchronous USB receiver to a DAC chip, to create a complete USB/analog converter (footnote 1). This they have done with the subject of this review, the DAC HD. Initially priced at $550, the DAC HD will be available for $495 by the time you read this review.

Asynchronous Conversion
Like the Bridge, the DAC HD includes captive cables, in this case a black version of Wireworld's Starlight USB cable, which features silver-clad conductors and a unique geometry said to allow use in lengths up to 7m. (A 2m cable is standard; 7m and other lengths are available as options when ordering.) Analog output is via two 6" lengths of silver-conductored cable terminated in Eichmann silver Bullet RCA plugs. (These RCAs are favorites of mine because they make the ground before the signal connection—a commendable feature.)

The circuitry, all surface-mount, is contained in a small (1.875 cubic inches), black-anodized, machined-aluminum enclosure, and is carried on a small double-sided printed circuit board. Power is taken from the 5V USB bus and first filtered (two-pole passive), then regulated; there are eight regulators and separate power rails for the digital circuitry, the master clock, and the output stage. The TAS1020B is mounted behind the USB port and feeds a Wolfson WM8716 DAC chip—a two-channel, multi-bit, sigma-delta, 24-bit type. Although the WM8716 can operate at sample rates up to 192kHz, the TAS1020B handles sample rates only up to 96kHz, including the important 88.2kHz rate. The Wolfson DAC includes fast- and slow-rolloff digital reconstruction filters, but also can be used with an external filter. The output stage uses high-performance op-amps.

No driver programs are required with either Macs or PCs. The user simply plugs the DAC HD into one of the computer's USB ports and selects it as the preferred audio output device.

Sonics
As I was about to start this review, I retired my 2006-vintage G4 Mac mini and replaced it with a 2.7GHz, i7-powered Mac mini with 8GB of RAM. Both the Mac mini and the Pure Music program recognized the Halide when I plugged it in, and I set it as the default playback device. Pure Music was set to upsample CD-sourced files to 88.2kHz with its Maximum Fidelity sample-rate converter.

Halide Design states that the DAC HD is cryogenically treated to give a "smoother, more resolved sound." Whether or not that was the reason, my first impression was indeed of a very smooth sound. There wasn't quite the wealth of recorded fine detail that I'm used to hearing with the megabucks D/A converters that usually grace my system, nor was there quite as expansive a soundstage. In my recording of Carol Wincenc performing Mozart's Flute Quartet in D, K.285, at the Santa Fe Chamber Music Festival (ALAC file sourced from CD: Serenade, Stereophile STPH009-2), while the flute was unambiguously placed in front of the string trio, the acoustic of St. Francis Auditorium sounded a little smaller and drier than it should. But that was a minor criticism, considering that when I rose from the listening chair to find my notebook, I realized I had listened to all three movements of the quartet. There was something very seductive about the sound of the DAC HD.

I don't care. I have never paid to download or stream anything, and I probably never will. My priority is to get the most from the several thousand CDs I already own. As cheaply as possible, without "adopting" anything, early or late. Yet I love computer audio when it's fast, fun, and free.

That's why I love inexpensive digital-to-analog converters. Buy one, use it for a few years, and replace it when something better comes along. The Musical Fidelity V-DAC II has come along ($379).

The original V-DAC sold for $299, and I reviewed it in the May 2009 Stereophile (Vol.32 No.5). It was small—3.75" (95mm) wide by 1.7" (40mm) high by 6.7" (170mm) deep—and powered by a wall wart. It accepted RCA and TosLink optical S/PDIF inputs that upsampled to 24-bit/192kHz, and a USB input that was limited to 16/48: still good enough for Internet radio, I think.

The V-DAC II is the same size and uses the same DSD1792 chip and SRC4392 upsampler, both from Burr-Brown. Unlike the V-DAC, the II incorporates the same asynchronous USB-to-S/PDIF converter found in Musical Fidelity's V-Link ($169), which the V-DAC II renders redundant.

The machined aluminum of the II's front and rear panels replaces the V-DAC's drab black and garish lettering, which reminded me of the jumping beans I used to play with as a kid. A toggle switch selects between the S/PDIF and USB inputs.

I no longer have the original V-DAC—my son got it last Christmas. (Now he's going to want the V-DAC II.) Even so, I could tell that the new version's sound surpassed the original's, even though I didn't use its USB input—I want nothing to do with paid downloads.

I heard more resolution, especially space. (Sam loves space.) A sweeter, less fatiguing treble—just the thing to show off the Dynaudio Focus 160 speakers. Better . . . well, focus. I could more precisely pinpoint images. In other words, I heard more where there, as well as more there there. And this is compared not only to my feeble memory of the original V-DAC's sound, but also to the sound of my present M1DAC. The new V-DAC is quicker, smoother, more agile. Who should know better than Quicksilver Audio?

For the most part, I used the Conrad-Johnson ET3 line stage and Quicksilver Silver 88 mono tube amps. I also used the LFD Mk.IV LE integrated. I mostly listened through the Dynaudio Focus 160s.

I was going to give Musical Fidelity's Antony Michaelson a bell, as they say in Britain, but he beat me to it. (I used to give my late friend Lars a yingle.) "The V-DAC II reclocks and upsamples to 24-bit/192kHz, whether you use S/PDIF or USB," Antony told me. (It's so easy to interview Antony. Like a good politician or general, he interviews himself.) "There's a profound question hidden here, which people sidestep. How can you turn 16 bits into 24 bits because it never was 24 bits? [But when you upsample] you're actually moving all the noise, all the crap, way out of the audioband, so it no longer interferes with the musical signal.

"This is simplistic," Antony continued, "but you can think of it like Dolby noise reduction. They boosted the midrange signal. The noise underneath remained the same, but the signal was bigger relative to the noise.

"The other interesting thing the V-DAC II does is reclocking. Every input has the same jitter. You don't lose the actual packet of data. It's still there, but you might not be sure of the starting point, and that's what causes jitter. The data packet is thrown off track. Reclocking lets you get the data back."

Antony told me that the V-DAC II's total harmonic distortion (THD) is less than half that of the V-DAC. "The crosstalk is dramatically improved, to 105dB, vs 94 or 95dB with the original V-DAC. This is what gives the superior stereo separation."

That pinpoint focus, if you will. This is very much audible, especially with Dynaudio Focus 160 loudspeakers!

While admitting the sonic superiority of genuine 24/96, Antony was no more eager to kill off the CD than I am: "Really good 16-bit/44.1kHz upsampled like this is really fantastic, but most people haven't heard it."

I have. For $379, you can, too.

John Atkinson, August 2012 (Vol.35 No.8)

The budget-priced Musical Fidelity V-DAC II is powered by a small wall wart. It has two digital inputs, S/PDIF and USB, selected with a small toggle switch. The S/PDIF input is offered on both TosLink and coaxial jacks, but only one can be used at a time. There is one set of analog outputs, single-ended on RCA jacks. The original V-DAC was reviewed by Sam Tellig in November 2009 and cost $299. Originally priced at $349, the V-DAC II now costs $379 but incorporates the asynchronous USB data receiver of Musical Fidelity's V-Link ($169), which allows the V-DAC II to handle data with a 24-bit word length and sample rates of up to 96kHz rather than be limited by the original's 16 bits and 48kHz. It still uses Burr-Brown's DSD1792 D/A chip and SRC4392 upsampler chip, however. Although the V-DAC II is $100 less expensive than the Halide DAC HD, the cost of cables brings its price closer to that of the Halide.

As with the Halide, setting up the V-DAC II is no more complicated than plugging it into a USB port on the host computer. Neither converter sounded harsh, which is what you might expect from inexpensive DACs. I agree with Sam that the Musical Fidelity had a sweet, nonfatiguing sound, though the Halide was, if anything, even sweeter. The V-DAC II had somewhat more extended low frequencies than the Halide. I had recently ripped to Apple Lossless files the Gary Burton Quartet's groundbreaking 1969 album Lofty Fake Anagram (CD, One Way). The Halide kept a little better control of the lows of, for example, Steve Swallow's double-bass solo in "Good Citizen Swallow," while not having as much weight. However, the Musical Fidelity's extra low-frequency energy is not as well controlled as it might be. The admittedly overwarm double bass in "Killing the Blues," from Alison Kraus and Robert Plant's Raising Sand (ALAC file transcoded from FLAC download with Max, Rounder/HDtracks 11661), was a bit too fat with the Musical Fidelity compared with the Halide.

More significant, the Musical Fidelity sounded drier than the Halide DAC HD, there being a little less of the St. Francis Auditorium's ambience audible with the Mozart Flute Quartet from my Serenade recording (Apple Lossless file, ripped from CD, Stereophile STPH009-2): the violin, viola, and cello were presented as being more in the same plane as the flute. Overall, this aspect of the Halide's sound pushed it ahead of the V-DAC II for me, for whom "more space" is always more better. However, it's fair to point out that the Musical Fidelity is more versatile than the Halide, having both coaxial and TosLink S/PDIF inputs as well as USB.—John Atkinson

Thus spoke AudioQuest's Steve Silberman, VP of development, of their brand-new USB D/A converter, the DragonFly. "There are a lot of very good DACs out there," he continued. "There are even a lot of very good affordable DACs. But the problem is, people outside of audio don't want them: They don't want old-style components like that.

"I know a lot of people who have started and sold companies, who could have anything they want. People who love music. And they don't want what our industry makes. For so long, our industry has dictated to the customer: 'You want to play CDs? You need a CD player, and this is how it has to be.' Same thing with DVDs and lots of other things: The manufacturers and the retailers dictate to the customers. I wanted to make a really high-quality audio product that meets people on their own terms."

The product that Silberman and AudioQuest had in mind was an outboard D/A converter that would sell for the same price as an Apple iPod Classic: a mere $249. The AudioQuest DragonFly measures 2.5" long, weighs three-quarters of an ounce, streams up to 24 bits and 96kHz, and plugs directly into the user's laptop or desktop computer. And it's a heck of a thing.

Description
Ideas in mind, Steve Silberman approached Gordon Rankin, the man who created what many of us regard as high-end audio's first USB D/A converter: the Wavelength Audio Crimson. The Crimson, which went on sale in 2004, wasn't Rankin's only computer-audio first. He also invented the first cross-platform asynchronous USB protocol, which allows the clock in an outboard DAC to override the clock in the datastream coming from the computer—the native frequencies of which are mathematically unrelated to audio sampling rates, to near-catastrophic effect in terms of timing errors, or jitter. Rankin has since licensed that code, given the trade name Streamlength, to a number of well-known manufacturers, and it now resides in the ROMs of many computer-audio components that have received glowing reviews in Stereophile.

The Streamlength software resides on the Texas Instruments TAS1020 controller board inside the DragonFly: one of three chips at the heart of the new converter. Rankin, who designed every aspect of the DragonFly except its connectors and cosmetics, says that AudioQuest expressed admiration for the Wavelength Proton D/A converter ($900; see my review in the October 2011 issue). Thus he began by basing a prototype on the Proton's Wolfson D/A chip. "I got it working," Rankin says, "but, for me, there was something lacking. I asked [AudioQuest] to let me do whatever I wanted, and so I ended up using the 24-bit ESS Sabre DAC." A Burr-Brown headphone amp/line amp, incorporating a 64-step analog volume control, completes the picture.

Rankin seems almost surprised at how well the finished DragonFly turned out—but he adds, with a laugh, "You don't know how much of a pain in the ass it was to get it that small! There are 107 parts inside, including five regulated power supplies." The scale of the thing's innards are typified, Rankin says, by the 1mm microdot LEDs that enable the dragonfly emblem on the DAC's zinc-alloy case to change color in accordance with the sampling rate of the file being played: green for 44.1kHz, blue for 48kHz, amber for 88.2kHz, and magneta for 96kHz. Yet for all that, the DragonFly is made in the USA.

Last but not least, the DragonFly's connectors are the sorts of things one might expect from a maker of perfectionist-quality cables: Its 3.5mm jack and USB plug feature silver-plated contacts. is machined from a compound of copper and beryllium (the latter said to add strength and elasticity), while the USB pins are copper. Both connectors undergo AudioQuest's direct-silver plating.

Installation and Setup
Installing the AudioQuest DragonFly, which is designed to work with the latest versions of Microsoft Windows and Apple OS X, took a little less than 15 minutes. Physical installation consisted simply of plugging the unit's integral USB plug into an available jack on the back of my Apple iMac and fitting the 3.5mm jack at the DragonFly's other end with an appropriate audio cable (about which I'll say more in a moment). Finishing the job was a simple matter of clicking on the Mac's Systems Preferences window (footnote 1), clicking the Sound icon, and then, under the Output tab, selecting "AudioQuest DragonFly," which appeared there as if by magic. (Under the Sound Effects tab I selected Internal Speakers, thus denying myself the pleasure of using a five-figure music system to alert me to every new kitten photo on Facebook.)

I mentioned the DragonFly's 3.5mm output jack, which might pose a challenge to The Unprepared. I still have a mini-plug-to-phono-jack adapter left over from my days as a Sony Walkman Pro owner, but I didn't press it into service. Rather, I accepted the loan, also from AudioQuest, of one of their new single-run Bridges & Falls interconnects. The interconnect cable I borrowed is a 5m run of AudioQuest Yosemite, with a 3.5mm plug of silver-plated "red" copper at one end, a pair of RCA plugs of the same composition at the other end, perfect-surface copper+ conductors, fluoropolymer air-tube dielectrics, and AudioQuest's 72V dielectric bias system: a sophisticated cable by anyone's definition. The retail value of this 5m Yosemite cable—the second-most-expensive in the Bridges & Falls line—is $1395. (I'm cheered by the existence, at the other end of the range, of the Evergreen single-run cable, which would sell for $53 for this configuration and length. I look forward to trying it.)

I've used a few different Mac-based music players in recent months, with still more on my to-do list. My reference remains Decibel v.1.0.2, by Stephen F. Booth Software, but rest assured—there are more than just one or two very good players out there. If you're still using iTunes, you're not getting the performance of which your system is capable, plain and simple.

Then, at the 2011 Rocky Mountain Audio Fest, I was given a dem of what I at first assumed was a QB-9—until I saw the bar-graph level meters to either side of the sample-rate display. This was the QA-9, a high-performance analog/digital converter, housed in the same chassis as the QB-9 and intended to allow audiophiles to make rips of their LPs of the highest quality possible.

The QA-9 operates at sample rates up to 192kHz, outputting 24-bit data either by a USB 2.0 connection or by AES/EBU. (The two aren't operational at the same time.) The basic version costs $3950; a Pro version, which includes DSD and Word Clock outputs on transformer-coupled BNC jacks, costs $4750. Given my extensive experience of both domestic and professional A/D converters, which has convinced me that the most critical process in digital recording is the initial analog/digital conversion—nothing downstream can put right whatever was done wrong in that conversion (footnote 1)—I asked for a production sample of the QA-9.

Design Philosophy
Via e-mail, I asked Ayre's founder and designer, Charlie Hansen, why a manufacturer exclusively known for its domestic high-end audio products had ventured into a field dominated by pro-audio companies.

"If we build, say, a great preamplifier, then one audiophile will be able to bliss out on the music. On the other hand, if we build a great A/D converter, then literally millions of people could benefit from the improved sound. Several professionals own Ayre equipment, usually for their home systems. Somewhat typical but most notable is Rick Rubin [record producer and founder of American Recordings and Def Jam Records]. He says that Ayre makes the best-sounding digital playback gear, and he has been after us for years to build equally good-sounding recording gear.

"To my knowledge, nobody has ever built an ADC with fully discrete, fully balanced, zero-feedback analog circuitry. In my experience, the single most important factor in getting good sound in digital audio is with the analog circuitry, so that was reason enough to start the project. Of course, we at Ayre are never content to rest on our laurels, so we also incorporated a slew of other innovations."

The heart of the QA-9 is the AT1201, a two-channel A/D converter chip that is new to me, from a company also new to me: Arda Technologies. The chip's datasheet describes it as an "advanced multi-bit sigma-delta" converter that will operate up to a sample rate of 384kHz with an astounding dynamic range of 124dB.

"Arda does consulting work for big contractors. They are audiophiles, and in their spare time designed and built a new A/D chip that clearly outperforms anything from the competition. Specifically, the out-of-band noise is ridiculously low, and this gave us a lot of freedom to 'think different' (as Apple ungrammatically said a couple of decades ago)."

What did Hansen mean by "think different"?

"Ever since DSD was announced, it has received uniformly positive comments on the sound quality. . . . [T]o be honest, we were basically baffled by Sony's original marketing material. We couldn't figure out how the system worked, let alone why it sounded good. But over the years, not only did more and more information leak out, but our understanding of digital audio at Ayre grew rapidly.

"In short, the reason that DSD sounds as good as it does is because there is no filtering done on the record side. The playback side requires a filter (per the Scarlet Book specs), but compared to the brick-wall filters used in typical PCM products, this is a much, much gentler affair. When we developed the QB-9 we spent nearly four months performing listening tests on digital filters. It was clear that both the anti-aliasing (record) and reconstruction (playback) filters had a very strong influence on the sound of digital audio (remember how the 'non-oversampling' DACs were quite popular for a few years?), and so we wanted to really understand what was going on. . . .

"The relatively recent advent of using the personal computer as a way to store and play back music files has changed the game entirely. Now we can buy, store, and play back music at quad-sample rates [176.4 and 192kHz] (or even higher), if so desired. But the problem is that digital audio equipment is still designed by digital audio engineers, traditional engineers, who, if they are using a 192kHz sampling rate, are going to make their equipment with flat frequency response to 96kHz and then just put a brick-wall filter on it. Fortunately, I am not a traditional digital audio engineer! I therefore have the freedom to ask 'Why?,' and I do that a lot!

"So for the QA-9 in Listen mode, we decided that the goal was to make the converter operating at the quad-sample rate to perform more or less like a perfect 30ips analog tape machine. The frequency response is down about –3dB at 50kHz, but it goes down to around 1Hz with no 'head bumps' to worry about. There is zero wow and flutter, and the distortion and noise are about an order of magnitude better (ie, 20dB) than the best analog tape machines.

"Yes, the anti-aliasing filter (in Listen mode) is down only about 20dB at the aliasing point of 96kHz, but is that really a problem? Do any recordings actually have any meaningful amount of musical energy up at 172kHz, where there would be aliasing that would fold down into the audioband?

"Of course not! There aren't many instruments with significant amounts of energy above 90–100kHz. Nor are there many microphones with any significant response this high. Or mike preamps. Or mixing boards. Or whatever.

"So the first thing that we did was to use a completely different type of digital filter at the output of the delta-sigma converter. (Every audio ADC chip made for the last 20 years has been a delta-sigma type, as the competing successive-approximation devices died off long ago.) Instead of using the normal low-pass Finite Impulse Response (FIR) filter to turn the output of the delta-sigma DAC into PCM, we use a moving-average filter. This doesn't just allow for improved transient response, but actually perfect transient response. And since we are starting with a 256Fs [11.2896MHz] sample rate, we don't have the problems exhibited by 'non-oversampling' DACs that also have 'perfect' transient response. There is no pre-ringing, no post-ringing—no ringing whatsoever. (This is in the Listen mode at both the quad and double sampling rates. It is not possible to use this trick at the single sample rate, where instead we use a more conventional FIR low-pass filter, but of course this is a slow-rolloff design to minimize ringing, and also is a minimum-phase design, so that all of the ringing occurs after the transient, with no unnatural 'pre-echo' before the transient occurs.)

Among average consumers of a certain demographic and audio hobbyists alike, computer audio is now regarded as commonplace; on the bright side, and notwithstanding the sudden shortage of consumer awe and wonder, the industry that serves the latter segment of the population now seems distinctly interested in the former, and is responding with a steady stream of perfectionist-quality USB digital-to-analog converters priced below $500. Indeed, in 2005 I wrote one of Stereophile's first reviews of a USB DAC—the fine-sounding Wavelength Audio Brick, then priced at $900—and today, less than eight years later, I am conditioned to expect ever-higher levels of performance for ever less money.

A case in point: the sleek new iDAC D/A converter ($299), one of the first four products from iFi Audio, a subsidiary of Abbingdon Music Research. (You'll recall AMR as the London-based design and manufacturing firm whose flagship DAC, the DP-777, I reviewed in these pages in March 2012.) During the second half of last year, Vincent Luke of iFi/AMR and Darren Censullo of Avatar Acoustics (which distributes iFi and AMR products in the US) stopped by with loaner samples of the iDAC and its optional power-supply upgrade, the iUSBPower ($199). Their visit stands out in my mind because my dog, Chatter (footnote 1), was being especially fiendish that day. I remember it for other reasons, as well.

Description
The iDAC, designed in the UK and assembled in the People's Republic of China, is built into a 6"-long aluminum extrusion with an attractive textured finish. All of its parts and circuitry are arranged on two printed-circuit boards, each measuring 2.75" by 2.25": One contains the USB receiver and clocks, the other the power supply and headphone amplifier. The latter board is also home to a pair of RCA jacks for line-level output, along with a volume pot for the headphone amp and a 3.5mm headphone jack of seemingly higher-than-usual quality. The two PCBs are held stationary by two slots that are integral to the inner surface of the case; beyond that, the boards are connected to each another by means of only a 12-pin socket and plug. Whether that arrangement confers some degree of mechanical isolation between the boards is anyone's guess, but, as Ernest Hemingway once said, isn't it pretty to think so?

Since the introduction, in 2005, of Gordon Rankin's oft-licensed Streamlength program—the first commercial software to allow a USB-connected, streaming-audio device to generate its own master clock, independent of the incoming computer signal—a few perfectionist-audio companies have developed their own such programs for asynchronous streaming. This is true of the iDAC, whose USB control software was designed by parent company AMR. That software resides in a flash-memory chip on the receiver board, and is upgradable by means of the control-panel application on the user's computer, should the need arise. The software runs on a British XMOS microcontroller—Vincent Luke describes it as "roughly something like a mid-1990s Pentium PC on a chip"—and the USB receiver is the USB3318 chip from Smart Mixed-Signal Connectivity (SMSC), of Hauppauge, Long Island.

Which brings us to the real star of the show: the Sabre DAC from California-based ESS. As implemented by iFi, this 24-bit/192kHz chip performs its own current-to-voltage conversions, and directly drives the iDAC's line-level outputs. As well as the two RCA jacks for the line output, the iDAC's front panel sports a 3.5mm headphone jack with an associated volume control.

The iUSBPower, which is identical to the iDAC in size, weight, and general appearance, is described by iFi Audio as a quiet, pure, well-regulated 5V power supply suitable for use not only with the iDAC but with any low-current 5V device that gets both its operating voltage and digital signal through a USB Type B socket, in accordance with USB 2.0 protocol. The iUSBPower, which is powered by a 9V wall wart of unremarkable appearance, is meant to be installed between one's computer and USB DAC: A USB cable of the usual sort carries both DC and the digital signal to the Type B USB jack on one end of the iUSBPower, and another such cable carries DC and digital alike from a USB A socket at the other end of the iFi to the DAC of one's choice.

The iUSBPower has two more tricks up its extruded sleeve. In addition to the USB Type A input jack described above, it has a second such socket intended to receive DC only, without digital signal, this to take advantage of a forthcoming Y cable that will effectively separate DC (USB pins 1 and 4) from the digital signal (USB pins 2 and 3), for even less interference between the two.2 Additionally, the iUSBPower has a ground-lift switch, for those who wish to explore the potential for sonic enhancement that one grounding scheme may or may not hold over the other. Incidentally, the iUSBPower's case resisted my efforts to disassemble it, thus preventing me from commenting here on its construction; I assume the iDAC was intended to be similarly Sphinx-like, if not quite as impervious. (Neither review sample suffered any harm from my inquisitiveness.)

Installation and Setup
Although the packaging for both products was sophisticated and well done, neither the iDAC nor the iUSBPower came with much in the way of a user's manual: The owner must refer to iFi Audio's website for documentation, mildly annoying though it is.

Then again, installing these products wasn't terribly daunting. I've already described the iUSBPower's connection scheme, which is illustrated on the iFi website in the clearest of ways. As for the iDAC itself, connection to my Apple iMac was a simple matter of running a standard (Type A plug to Type B plug) USB cable from computer to converter, opening the iMac's onscreen System Preferences window, and selecting from the Sound/Output pull-down menu the listing for "AMR USB Audio 2.0," which appeared automatically. Users of Windows-based computers are directed to a page on the iFi website from which they can easily download the device driver required for their systems.

I experienced only one problem. When the iDAC was used on its own, without an accessory power supply, my iMac never failed to find and identify its resident software. But with the iUSBPower connected between computer and iDAC, the iMac was often unable, at first try, to find the converter at all: There followed, in such cases, numerous attempts at disconnecting and reconnecting the USB cable between the iFis until the AMR software would finally appear. That glitch occurred regardless of which brand, model, or length of cable I used in that position, and it was never resolved by a system reboot or any other means: Breaking and remaking the iUSBPower-to-iDAC connection, often as many as five or six times in a row, was the only way to get things running again.

A final setup note: Like all computer-audio products that weigh less than a half a pound, the iDAC and iUSBPower fell victim to the bullying effects of heavy, inflexible cables; through no fault of their own, lightweight boxes are easily pushed around, and are sometimes reluctant to stay put on the shelf or tabletop one has placed them on. For that reason alone, I didn't bother trying the iFis on isolation platforms/devices of any sort—which would have seemed silly in any event, in a corner of the market where one hopes to keep things cheap and easy. And happily so.

Listening
With music that challenges neither the frequency range nor the overall dynamic range of my gear, I did not, at first, hear much difference between the fine-sounding, musically convincing $299 iDAC and the slightly less expensive ($250) AudioQuest DragonFly—the latter having in recent months become my reference low-cost DAC. For example, with Joe Pass's classic solo-guitar performance of "Stella by Starlight," ripped from the XRCD of the first in his series of Virtuoso albums (JVC VICJ-60256), the two DACs were virtually identical to one another in timbral balance, spatial scale, dynamics, freedom from artificial grain and noise, and literally every other meaningful respect. (This was after I'd matched the converters' volumes, the iFi iDAC having a notably higher output.) Yet when I moved on to something with wider frequency and dynamic ranges—for example, "The Ballad of Albatross and Doggerel," from the dB's' new Falling Off the Sky (CD, Bar None BRN-CD-210)—drum flourishes, electric-bass–note attacks, and the like impressed me as having slightly more impact through the iFi.

The iDAC also bested the DragonFly by a slight margin with King Crimson's In the Court of the Crimson King (ripped from CD, EG DGM0501), most notably by offering a better, more realistic sense of touch. Through the iDAC, the arpeggio-like descending figure that Robert Fripp plays behind the chorus of "I Talk to the Wind" sounded, quite simply, more guitar-like, with more apparent pressure on the strings—especially on the slides, and on that lovely, subtle bend from E to F-sharp near the chorus's end. The light drumming in the improvisational section at the end, too, was more forceful through the iDAC, as were the vibes in the improvisational section of "Moonchild."

And when the iDAC was used to play acoustic music of more generous bandwidth, the gap between it and the DragonFly widened further. The iDAC did a better job of portraying natural textures, chiefly by seeming to enhance those subtle contrasts that convey sonic "relief"—as with cellist Pieter Wispelwey's sumptuous string tone in Bruch's Kol Nidrei, with Daniel Sepec conducing the German Chamber Philharmonic Bremen, ripped from the CD layer of a hybrid SACD (Channel Classics CCS SA 16501). Actually, the iDAC and this recording suited one another in a variety of ways: In addition to sounding perfectly, vibrantly thrummy, the soloist's cello had a fine, dark timbral balance, with the right sense of physical scale; musically, the iDAC-driven system found the piece's melodic structure and sang it, without distorting its momentum and flow. Even now, I look back on the time I spent listening to this recording through the iDAC, my Shindo Haut-Brion amp, and the big old Altec Valencias as one of the finest, most mesmerizing digital-audio experiences I've had.

Footnote 2: This use of power-supply cabling to carry both DC and signal reminds me of the classic Naim Audio gear of the 1970s and '80s.

On the contrary, the arrival of each new Music Streamer is cause for celebration by those of us who want to know: How much more performance—and for how small a price—can we have today? HRT's answer for 2013 is their new Music Streamer HD ($449.95), which promises also to keep pace with the industry's growing library of high-resolution downloads.

Description
The Music Streamer HD is built into a lightweight aluminum extrusion 5.5" long and 3.5" wide, with plastic endcaps molded to suggest the same texture as the case's finish. One end is devoted to analog connections, with RCA jacks for single-ended signals, and a pair of XLR sockets for people whose systems can accept fully balanced signals: one of the new DAC's calling cards. The other end is home to a USB type B input jack, a bee-stinger–sized switch for selecting from USB 2.0 to 1.0, for those with older computers, and two groupings of indicator lights: a six-light bank for the common sampling rates from 44.1 to 192kHz, and three lights indicating 16 bits, 24 bits, and mute.

Like the Music Streamers II and II+, which I reviewed in the December 2010 issue, the Music Streamer HD is built on a single printed-circuit board, held in place by ribbing inside the case; the HD's roomier chassis, compared to that of its predecessors, seems necessary only inasmuch as its XLR sockets require a larger mounting area than RCAs. Analog output circuitry occupies the end of the PCB nearest the line-level audio jacks, while place of honor at the center of the board is given to a Burr-Brown PCM1794—a 24-bit/192kHz processor with its own 8x-oversampling digital filter—with current-to-voltage conversion handled by a differential stage outside the D/A chip. An XMOS microcontroller, supplemented with a Winbond flash memory, handles USB communications: The Music Streamer HD is an asynchronous device, using proprietary software written for that purpose by designer Kevin Halverson.

Also in common with Music Streamers past, the HD omits an outboard power supply, depending instead on the kindness of the USB bus and the voltage available thereby. Here the HD enlists the help of a CUI integrated DC-to-DC converter, which converts 5V DC into separate positive and negative swings, thus making a total of 10V available for distribution throughout the board.

Installation and setup
These days I expect few difficulties installing computer-audio products, in which regard the Music Streamer HD proved blessedly unexceptional. With the HRT connected to my Apple iMac by means of an AudioQuest Carbon USB cable, I simply clicked on System Preferences, then Sound, noting from the latter that the HRT identified itself as, simply, "USB 2.0 Audio Out." Throughout the review period, my computer never failed to detect and correctly identify the Music Streamer HD.

Because my Shindo Masseto preamplifier isn't designed for balanced sources, I relied mostly on the Music Streamer HD's single-ended outputs. Those jacks are installed quite close to one another—about 0.56" apart, measured on-center—but there was enough room for two RCA plugs of reasonable bulk. That said, I noted that the HD's jacks were mounted on the softish plastic endcaps rather less than rigidly, and thus were not immune to wiggling when I used bulky plugs and cables.

During the review period I had the good fortune to receive an integrated amplifier designed for fully balanced throughput—the new and very interesting Ayre Acoustics AX-5—thus providing the chance to try the HD's solidly nice XLR sockets; I used a 1m pair of Nordost Tyr interconnects I'd borrowed a while back, to review Ayre's own QB9 processor. (Before dropping entirely the subject of Ayre Acoustics, I'll mention also that their otherwise useful Myrtle Block isolation devices did not come into play during this review: Like most relatively inexpensive USB DACs, the Music Streamer HD seemed too light in weight to benefit from the use of those or other such things. I contented myself with keeping the review sample on a small pinewood table.)

Two final setup notes: Following USB connection to my computer, the Music Streamer HD became slightly—almost imperceptibly—warm to the touch, though not as warm as earlier HRT DACs. (I would imagine that this, too, is a function of the HD's roomier chassis.) And throughout my time with the HD, regardless of the music file being played, the processor's 24-bit indicator remained illuminated, its 16-bit indicator dark, even when I played a 16-bit file. (The Mute light at the bottom of the same bank of indicators could be toggled on and off with my iMac's F10 key—which did effectively mute and reactivate the HD.)

Listening
After a break-in period during which the Music Streamer HD suffered the indignity of supplying party music—highlights included some of the weaker selections by my heroes Ian and Sylvia, along with about three quarters of Sinead O'Connor's Am I Not Your Girl? (the three-quarter mark signaling the very end of my patience with that recording's extravagantly hokey instrumentation)—the new HRT processor went to work in my reference system.

Yet more good news comes in the form of Meridian Audio's Explorer ($299), a 4"-long USB digital-to-analog converter from a company that many hobbyists would name as one of the industry's premier digital specialists. That the Explorer is available not only at traditional Meridian dealers but also at a growing number of single-brand Meridian boutiques—locations now including Fort Lauderdale, Moscow, and Kuwait—may be seen as icing on the cake.

Ken Forsythe, Meridian America's director of product development, says his company hasn't turned its back on the high-end audio and video markets. "But if we want to be around 100 years from now, we have to go beyond our core. We think of computer-centric users as the new enthusiasts, so the question becomes: How, over time, can we grow them into core customers?" The answer, Meridian believes, is in the form of this, their first portable processor.

Description
Shaped like a Bic disposable lighter and sized like a Pez dispenser, the Explorer is built into a lightweight aluminum alloy tubewith a hard-anodized finish. A plastic cap at one end incorporates a USB mini-B jack—chosen because a full-size B jack would subject the internals to excessive stress—while a similar cap at the other end holds two 3.5mm jacks: one for headphones, the other for line-level audio output. The latter is combined with an optical digital-audio output—rather like the headphone jack on the back of an Apple iMac—to address the TosLink input of any outboard D/A converter. One might see that as an effort on the part of Meridian to emphasize both the Explorer's portability and its usefulness in a domestic system that already contains a high-end processor from Meridian (or anyone else, for that matter).

The Explorer requires only 5VDC, which it gets from the USB bus of the associated computer. It operates in asynchronous mode, using Meridian's proprietary software to reclock the incoming datastream. The converter chip of choice is the 24-bit/192kHz PCM5102 from Texas Instruments, followed by an analog section that Meridian describes as containing especially good-quality parts for one so humble. (As I could find no way to crack open the Explorer without destroying its aluminum shell, I didn't go poking around.) The Explorer's 130mW headphone output incorporates a 64-step analog volume control, while the line-output jack itself is fixed in level.

While I wasn't able to see for myself the Explorer's build quality, I can nonetheless comment on the whereabouts of its construction: Meridian's least expensive product is, like the rest of their line, made in England. Ken Forsythe relates this, too, to the company's efforts at "building their brand," so that new customers might someday step up to Meridian's more expensive gear: "We couldn't build products overseas and still be able to look our new customers in the eye and say, 'This is built in the same place as our finest products.'"

Installation and setup
In addition to a black-velvet travel pouch—another inducement to portability!—the Meridian processor is supplied with a very flexible 6" cable, used to connect the USB-A socket of the associated computer with the mini USB-B socket of the Explorer. As far as I can tell, there exist no aftermarket, perfectionist-quality versions of this digital cable; I'm keeping my fingers crossed that, if and when that day comes, the industry will keep stiffness, expense, and speculative fiction to an absolute minimum.

There do, however, exist aftermarket cables for use with the audio-out jack at the Explorer's other end: a genre in which AudioQuest has recently become a major player, owing to the use of a 3.5mm output jack on their own DragonFly DAC. For the Meridian converter, I used the same 5m length of AudioQuest Yosemite—a three-conductor interconnect with RCA plugs on one end and a 3.5mm mini-plug on the other—that I used when I reviewed the DragonFly in October 2012.

As with most contemporary USB DACs, getting the Meridian Explorer and an Apple iMac computer to play nicely with one another was as easy as losing one's health insurance. After connecting the USB cable and opening the Sound window of my G5's System Preferences menu, I found the review sample listed as "Meridian Explorer USB DAC Out"; once I'd selected it, neither the Explorer nor my iMac ever seemed to forget the other. Explorer owners who wish to use their new converter with a Windows operating system must first visit the Meridian website and download and install the appropriate driver file. (The OS specs for PCs listed on Meridian's website are "Windows XP SP3, Windows 7 SP1 or Windows 8.")

Once the Explorer is powered up, three small, white LEDs on its upper surface light up; after data streaming begins, the pattern of lights changes to inform the user of the resolution of the incoming music file: one light for 44.1 or 48kHz files, two for 88.2 or 96kHz, and three lights for 176.4 or 192kHz. This is in marked contrast to those processors on which a single light is likely to correlate with mathematically related combinations of frequencies; eg, 48 and 96kHz.

Because the Meridian Explorer weighs just slightly more than a cookie, placing it atop any sort of "isolation" accessory seemed even more ridiculous than usual. So I didn't.

Listening
A few days after my review sample of the Meridian Explorer arrived, I set about running it in. In retrospect, given how little this changed its sound, the new converter didn't particularly need it, but I nevertheless enjoyed the time I spent using it to hear my favorite Internet radio stations, during which casual listening the Explorer's tonal balance and spatial presentation were almost indistinguishable from those of the similarly priced and sized AudioQuest DragonFly. (I was helped to that early conclusion by the fact that the two devices are also very similar in apparent output voltage.)

The first serious listening I did with the Explorer was to the classic bluegrass album Appalachian Swing!, by the Kentucky Colonels, featuring Clarence and Roland White on guitar and mandolin, respectively (AIFF ripped from CD, Rounder SS31). The Meridian was instantly impressive, with a sense of scale that was pleasantly big but still appropriate to the ensemble and their setting. The original recording is a bit light, but the Meridian Explorer retrieved from it almost as much timbral color as one might hope for. The same was true with the weight and color of Roger Bush's double bass—the Explorer was clear and unambiguous in portraying the pitches of individual bass notes, down to being coldly candid about Bush's dodgy intonation.

Subtle differences were apparent between the Explorer and the DragonFly, the former having considerably better channel separation. Although not as severely "two-channel mono" as, say, those early Beatles albums, Appalachian Swing! doesn't have a lot of center fill, a characteristic made all the more plain by the Meridian. Comparisons between the Explorer and the Halide DAC HD showed the latter to be a little meatier in the timbral sense—though one could, I suppose, turn that around and describe the Explorer as "airier." That said, I did prefer the richness of the Halide—which costs almost twice as much. All three products got across the essence of the White brothers' highly charged musical interplay, yet I dare say the Meridian was the most explicit, being clearly upfront about such subtle musical—not merely sonic—details as the bass lines that guitarist Clarence sneaks in behind brother Roland's mandolin solos.

Far be it from me to tell the players on Buena Vista Social Club (AIFF ripped from CD, World Circuit/Elektra Nonesuch 79478-2) that there's an overabundance of trebly percussion instruments in the opening measures of "Amor de Loca Juventud." That said, there was something in the sound of the Explorer that brought that quality to the fore. The Meridian wasn't bright, wasn't etched, and didn't lack bass, but there was a lightness—or a responsiveness to a lightness in the music, if you will—that highlighted those high-frequency overtones. The difference between the Meridian and AudioQuest processors was exceedingly slight in this regard: Even through the DragonFly, I found those opening bars a bit too mosquitoey, but the effect was ever-so-slightly more pronounced through the Explorer.

And yet—listening through the Meridian Explorer to Lee Feldman's brilliant "Do You Want to Dance?," from his Album No.4: Trying to Put the Things Together that Never Been Together Before (AIFF ripped from CD, Bonafide UM-130-2), I again heard a sound with a more silvery, more detailed treble range than through the DragonFly. Here, however, the slight distinction definitely favored the Meridian: The British converter made clearer the descending figure in the tremoloed electric bass, revealing a greater frisson of feeling.

Speaking of bass, the Explorer proved capable of communicating low-frequency tones with appropriately generous weight and power. The Meridian allowed just the right amount of force and purr to the double bass and bass drum in "Polly Come Home," from Robert Plant and Alison Krauss's Raising Sand (AIFF from CD, Rounder 11661-9075-2). The timpani that open the third movement of Mahler's Symphony 2, performed by Gilbert Kaplan and the London Symphony Orchestra (AIFF from CD, MCA Classics MCAD 2-11011), had fine attack and a degree of timbral richness in their decay that, while not the best I've heard from a USB DAC, was satisfying. Later in the same recording, the Meridian was more than satisfying in the way it communicated the sheer, monstrous weight of the assembled instrumental forces, organ and carillon included. Heard in concert, the ending of that symphony should leave one, if not in tears, then at least slightly misty; heard in my home, the Meridian did the job—which, at the end of the day, is the most important thing I could ask of it.

A brief mention is due of the Explorer's performance with headphones: a style of listening with which I'm less than experienced. My feelings belong in the file folder labeled "Musically Satisfying and Free from Gross Distortions, Although the Sound Was A Little More Opaque Than I Expected."

Conclusions
When it comes to inheriting the Earth, or at least that portion of it that wants perfectionist-quality sound from music files stored on computers, I think The Small are doing a damn good job of things this time around. Fonder though I am of analog playback, I take heart at digital audio's recent efforts in making products that normal people desire and can afford—a trend of which there is no finer example than the Meridian Explorer. It is robustly competitive in its price range, and although bettered by the considerably more expensive Halide, the Meridian is not embarrassed by it. And the choice between it and the similarly fine AudioQuest DragonFly may, for some, come down to nothing more mysterious than aesthetics, ergonomics, and the question of whether one wants a headphone jack or not.

Also as with the US-made DragonFly, I can't deny being impressed that the people who assemble the Explorer live and work in the same country as those who stand to profit from its sale.

A remarkably good addition to a burgeoning field—and an excellent value. Very highly recommended.

The front panel offers, from left to right: a Mode toggle to switch between internal and external clocks; a second toggle to select the sample rate (44.1, 48, 88.2, 96, 176.4, 192kHz) for the Main and Auxiliary outputs and to select ADAT or AES/EBU data formats; a third toggle to select the meter range (1dB or 6dB/division) and Peak Hold on/off; and a 2x9-LED level meter. Continuing to the right is a group of controls for the first channel, toggle switches to select gain (0, 10, or 20dB), Variable or Calibrated gain, and a rotary level knob; this group is then duplicated for the other channel.

The rear panel offers, from left to right: a pair of balanced analog inputs on XLRs; two unbalanced AES/EBU Aux outputs on BNC jacks; a USB Type-B port; a Main TosLink output working in either S/PDIF or ADAT format; a Main balanced AES/EBU output on an XLR; word clock input and output on BNCs; and the IEC AC inlet. The word clock ports allow the ADC1 to be used in multichannel applications, slaved to other converters. The Main USB, TosLink, and AES/EBU outputs always offer 24-bit data. The Aux outputs can have a different sample rate from the main outputs, to feed a CD-R or DAT recorder, and can be set to offer TPDF-dithered 16-bit data as well as the original 24-bit data. (TPDF stands for Triangular Probability Density Function, and refers to the spectrum of the dither used.)

Inside, the circuit layout is as clean and as logical as I have come to expect from Benchmark. The analog circuitry appears to be based on OP27, AD797, and LME49860 high-performance op-amps, while the A/D converter chip is an AKM 5394. This is a 24-bit, two-channel, 128x-oversampling, delta-sigma chip capable of operating up to a sample rate of 216kHz and with a high specified dynamic range of 123dB. A Texas Instruments TAS1020B is used for the USB interface, which limites operation via USB to sample rates of 96kHz and below. Two AD1896 asynchronous sample-rate converter chips are present, but I'm not sure whether they're used only to prepare the data for the Aux outputs or for a more fundamental purpose. Benchmark uses what they call UltraLock to reduce the level of jitter.

Sound Quality
I prepared some 24/96 needle drops using the ADC1 converter's USB output and the inexpensive Vinyl Studio app running on my MacBook Pro. In level-matched comparisons of "The Lark," from Moving Hearts'The Storm (LP, Tara 1304), with a 24/192 needle drop made with the Ayre QA-9 A/D converter ($3950) I reviewed in November 2012, the Benchmark had a little more weight and authority to its low frequencies, the Ayre a more delicately drawn soundstage.

The differences were in the same direction with a 24/96 transfer of English singer-pianist Peter Skellern performing "The Continental," from Astaire (LP, English Mercury 9109 702). The Ayre's imaging was a touch more palpable, the Benchmark's sound slightly more upfront, with firmer lows. But overall, the transfers from vinyl were more alike than different. I couldn't hear any meaningful differences between the Ayre and Benchmark converters with "Die Tänzerin," from Ulla Meinecke's Wenn Schon Nicht für Immer, dann Wenigstens für Ewig (LP, German RCA 426124).

I used the Benchmark last May as the master converter to record the final rehearsal of Bob Reina's band Attention Screen performing jazz compositions for trumpet, double bass, drums, and church organ. The outputs of the main pair of organ mikes, a pair of DPA 4003 omnis amplified by a Millennia Media preamp, were fed to the Benchmark running at 88.2kHz, with a Metric Halo MIO2882 used for the spot mikes on the other instruments slaved to the ADC1's word-clock output. The Benchmark's 24-bit AES/EBU output was fed to a Metric Halo ULN-2, and both Metric Halos were connected to my MacBook Pro via FireWire. That way, I could record all 10 channels using Metric Halo's multitrack Record Panel app.

Listening to the sound of the organ mikes, it was obvious that the Benchmark ADC1 had done a great job. With its clean high frequencies and weighty, extended lows, it faithfully captured the magnificence of the newly restored Ralph and Alice Greenlaw Memorial pipe organ at the Community Church of Douglaston, Queens. In the work intended to be the concert's finale, Bob gives the organ's bass pipes a workout—the last note, a sustained, lusty 32Hz C, shook the windows of my listening room.

Conclusion
Benchmark's versatile and full-featured ADC1 USB both measures superbly well and produces digital files that sound equally superb. It offers performance for which, a decade ago, you would have had to pay five times its price of $1795. It also offers better resolution than you get from inexpensive converters like E-MU's popular e404, whose nominally 24-bit A/D converter section actually has about 17-bit resolution. Unless the fact that, unlike the Ayre QA-9 it lacks DSD encoding is a problem for you, I highly recommend the ADC1 for transferring your LPs to digital.

There. I've said it. I am not an audiophile; ie, someone who's in love with recorded sound for its own sake. The search for ideal sound can leave a person burned out and broke.

That might be why I love Internet radio via Bluetooth. So much content. So convenient, via smartphone or laptop. As for computer-audio downloads, they're too complicated, chaotic, and costly.

I might pay for streaming high-resolution audio, if the content and convenience are there. More than one computer guru has said that digital subscriptions are the future. Who wants to "own" and store physical media?

I love Musical Fidelity's M1SDAC with aptX Bluetooth (see "Sam's Space" in October), even though my iPhone 4, updated to iOS 7, doesn't support aptX.

The aptX codec is said to automatically optimize the Bluetooth receiving device for the best sound quality possible with each incoming aptX signal. I have it now, with my new (June 2013) Macbook Air.

Is aptX a big deal? Some say it's not. As my colleague Bob Deutsch says, "It depends on the implementation."

AptX is back-compatible with earlier Bluetooth codecs. It streams at up to 380kbps, but it can work with devices that stream at lower bitrates, including 128 and 256kbps.

When my iPhone 4 ran iOS4, Bluetooth streamed at 128kbps, if I'm not mistaken. Now, with iOS7 installed, it streams at 256kbps, with better sound: more resolution, more air, fewer dropouts, more there there. If you have an iPhone 4 or later, it's definitely worth installing iOS7.

I'll pass along a couple of iPhone tips.

If you no longer get a Bluetooth connection, or you keep losing it, you may have a dirty dock. Some folks online have recommended that you brush around the dock's connections with a clean, soft toothbrush. Or flatten the tip of a cotton swab with a pair of pliers, dip it in grain alcohol, and wiggle it around. (I didn't tell you to do this.) This worked for a while.

Then, a genius at a bar told me another secret: Keep fewer programs running in the background. That was like a visit to the dental hygienist. Bluetooth became Cleanteeth: brighter, cleaner, more refreshing, less stale. Now the difference between my iPhone 4 with iOS7 and my Macbook Air with Mountain Lion running aptX Bluetooth was less pronounced. Of course, if you really want aptX on your smartphone or tablet, you can look to Samsung.

The Musical Fidelity MS1DAC sounds very good indeed; it's a DAC, a headphone amp, a line stage, and a headphone amp, all in one. But if all you want is aptX Bluetooth, you might not want to pay $1499 for an MS1DAC. You may already have a DAC you like. There must be a cheaper way to do this.

Ho, ho, ho, there is. At $249.95, the Arcam rBlink seems expensive for a tiny black box measuring only 2.9" (75mm) wide by 1" (26mm) high by 3.9" (100mm) deep and weighing just 12oz (350gm). But it will put Internet radio wirelessly at your fingertips, from laptop, tablet, or smartphone.

Arcam describes the rBlink as a "high-performance Bluetooth audio receiver and digital-to-analog converter." It works well, whether or not you already own a DAC. The rBlink has its own digital-to-analog converter and left and right analog outputs. Just connect it to your integrated amplifier or preamp. Arcam even includes interconnects to get you up and running fast. (But consider getting better interconnects.)

Don't dis the rBlink's built-in DAC, which uses Burr-Brown's PCM5102 DAC chip. It's no slouch, as the Brits like to say. Don't feel you need buy a separate DAC.

On the other hand, if you already own a DAC, you can use the rBlink's S/PDIF coaxial output. I used my Musical Fidelity V-DACII, now replaced by the V90-DAC.

I ran the rBlink into the Croft Acoustics Phono Integrated amplifier, first using the rBlink's analog RCA outputs and a decent set of interconnects. I cackled when I heard the sound. Art Dudley and Stephen Mejias are right: The Croft is crazy good in musical rather than in audiophile terms. You can tell from its rich, full-bodied sound that it wasn't designed with test tones in mind.

In the blink of an eye, I had Internet radio in excellent sound, depending on the quality of the stream.

Why are some streams so crummy—and from the same station? Classical New England—now re-rebranded as WCRB in order to show its real share in the ratings—broadcasts live concerts from its Fraser Performance Studio, always in excellent sound. Yet when they broadcast from Boston's Symphony Hall or Tanglewood, the sound deteriorates.

The day after I received the rBlink, John DeVore, of DeVore Fidelity, drove up to my digs with his new beast: the Orangutan O/93 loudspeakers. John groused but didn't growl about the Bluetooth sound, but that was before I got the Macbook Air and upgraded my iPhone 4 to iOS7.

I didn't let on to John, but CDs do sound better than Bluetooth at the moment. But we can expect Bluetooth to evolve and improve. It's one good reason not to plop down more than $249.

I rattled the zookeeper's cage.

"The sound is fine by me," I told John. "I just DeVore it. It's all free. Swiss Radio Jazz. Nostalgie Jazz. BBC 3. Classic FM. France Musique. Symphonycast.com. Radio Dismuke, with music from the 1920s and '30s. If I want Perfect Sound Forever, I'll get off my butt and fetch a CD."

Which brings up a point: I never found the rBlink irritating. Well, I did with a few piss-poor streams, but these are easily avoided. The rBlink seemed to hold on to the signal—fewer dropouts—better with my Macbook Air than with my long-in-the-tooth iPhone, until I installed iOS7.

The rBlink has one oddity: To pair it with a Bluetooth device, you need to push in the pairing button with the tip of a pen. I have no blinking idea why Arcam doesn't provide a simple pushbutton. While pairing, the rBlink changes from steady red to blinking purple. Pairing completed, the purple light glows steadily. When the rBlink is connected to a Bluetooth device, the light glows a steady blue. I love this thing!

Since the Croft's measurements rattled John Atkinson in October, I tried my LFD LE IV integrated amplifier. I got the same excellent results. The aptX codec no longer mattered so much, although you might as well have it, if you can.

If you're looking for a gift idea, and Mom and Dad have Bluetooth devices, put an Arcam rBlink under the tree. While you're at it, get another for yourself. You can bring Bluetooth to just about any audio device, including a kitchen radio.

Highly recommended.