Digital Processor Reviews

Bratty, mollycoddled, and altogether spoiled consumers such as you and I have inflicted on computer audio the same injustice that laparoscopic surgery, antilock brakes, mobile telephones, word processors, e-mail, microwave ovens, and over-the-counter proton-pump inhibitors have suffered at our hands in recent years: In less time than it takes to say "ho-hum," we've knocked it from the pedestal to which all such breakthroughs are entitled and begun taking it for granted.

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.

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Footnote 1: For reasons I don't fully comprehend, audiophile friends often hear my dog's name as Jitter.

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.