A computer is not optimized for the uninterrupted streaming of audio data. It has rapidly become established wisdom, therefore, that the optimal means of extracting audio data from a computer's USB port is to operate that port in what is called "asynchronous isochronous" mode. This lets the receiving device, such as a digital-to-analog converter (DAC), control the flow of data from the PC. In theory, asynchronous USB operation (not to be confused with the asynchronous sample-rate conversion used in some DACs) reduces jitter to unmeasurable levels, depending on the accuracy of the receiver's fixed-frequency oscillator, which is used to clock the data to the DAC. By contrast, in the alternative and almost ubiquitous USB operating mode, called "adaptive isochronous," while the sample rate of the output data, averaged over a longish period, will indeed be the specified 44.1 or 48kHz, there will be short-term fluctuations, or jitter, due to the oscillator having to change its frequency every millisecond to match the uncertain rate of data flow from the PC.
The standalone digital/analog converter emerged as a product category in 1987 with the appearance of the Arcam Black Box and the Marantz CDA-94, closely followed by the PS Audio Link. The idea was that putting the sensitive D/A-conversion and analog stages in a separate enclosure with its own power supply would maximize the sound quality when compared with packing these circuits in the same box as the transport. However, it turned out that the routing of the digital data between transport and processor in the form of an S/PDIF- or AES/EBU-encoded bitstream could introduce word-clock jitterwhich undid much of the sonic advantages. (See "Bits is Bits" by Malcolm Hawksford and Chris Dunn, Stereophile, March 1996.)
The X-DAC v3 replaces Musical Fidelity's Tri-Vista 21 DAC, which is no longer in production, although you might find some on dealer's shelves. The Tri-Vista 21 used two pairs of subminiature 5703 WB military tubes in the analog output stage. MF's Antony Michaelson called this Cold War tube, which is no longer made, a trivistor. The Tri-Vista 21 was last seen selling for $2395.
How do I get myself into these things? Knowing that I use a Musical Fidelity X-DACV3 D/A processor in my office system and had just auditioned the Bel Canto e.One DAC3 that he'd reviewed in November, John Atkinson asked me to give Musical Fidelity's X-DACV8 a try. I say "asked," but the man does authorize my paychecks, so I acceded, knowing I was painting a giant bull's-eye on my back.
Who wants only a digital-to-analog converter when you can have a DAC with benefits? How about if those benefits also come with some high-resolution attitude?
That's what I pondered while setting up the NAD M51 ($2000). Sure, it's a basic DAC, but it also has extraslike HDMI inputs, remote-controlled volume, a polarity switch, and one of my favorite features on any DAC: a display that tells you which sampling rate the thing is locked to.
Without having intended to, I seem to have collected several "statement" products. I've already reported on the Weiss Medea and Theta Digital Generation VIII digital-to-analog converters. I saw and expressed interest in the Nagra DAC at the 2002 Consumer Electronics Show, when prototypes of it were shown along with a forthcoming multichannel version, the Nagra Digital Audio Processor (DAP). The two units are based on the same chassis and interface, the DAP including additional modules and processing.
In an industry whose newest products are often as discouragingly unaffordable as they are short of the sonic mark, the Naim Audio Uniti ($3795) stands out. In a single reasonably sized box, the Uniti combines the guts of Naim's Nait 5i integrated amplifier and CD5i CD player with various additional sources: an FM/DAB tuner, and interfaces for an iPod, a USB memory stick, an iRadio, and a UPnP-compatible connected computer or serverall for the price of a very good television set.
Whether one was surprised, in 2010, by the success of Peachtree Audio's iDecco may have more to do with age than anything else. My peers and I wondered, at first, who would want their high-end integrated amps to come bundled not only with digital-to-analog converters but with iPod docks, of all things; at the same time, younger hobbyists wondered who in the world still wanted their integrated amps to contain phono preamplifiers. (Respect for the elderly, myself especially, prevents me from adding "and mono switches.") Color me chastened.
It's common knowledge that manufacturers tune the sound of each DAC model. There are the facts of product design and marketing: inputs, outputs, case materials, price points. After that, what's left are the trade-offs of different circuit designs and filter options, which are chosen with careeach has a subtle yet telling effect on a DAC's sound. Most designers try to go from bits to analog with minimal deviation from perfect. But when you look at the measurements and listen closely, you realize that perfect is elusive. One has to make choices.
Oh boy, another new DAC review. Some folks think DACs, once you get past the features, all sound pretty much the same. I mean, it's just digital. Well, they're right. Pretty much. Just as two new cars of a particular make, model, color, and options package both look the same, sitting there on the lot.
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 carmaybe 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.
As with so many other things, from cell phones to soy milk, the idea of a portable MP3 player was something I at first disdained, only to later embrace with the fervor of any reformed sinner. But not so the idea of a high-fidelity iPod dock: Given that I now carry around several hundred high-resolution AIFF files on my own Apple iPod Touch, the usefulness of a compatible transport seemed obvious from the start. Look at it this way: In 1970, whenever I bought a music recording, I could enjoy it on any player, in any room in the house. In 2010, why shouldn't I enjoy at least that degree of convenience and flexibilitywithout resorting to a pair of tinny, uncomfortable earbuds?
At the Consumer Electronics show in Las Vegas in January 1999, Mark Schifter, erstwhile president of Audio Alchemy, was handing out a press release announcing what seemed like a groundbreaking product from his new company, Perpetual Technologies. The product was the P-1A, a digital-to-digital processor that would do resolution enhancement, loudspeaker correction (amplitude and phase), and room correction—all for less than $1k. It sounded too good to be true.
"We like to make things," Roy Gandy, Rega's founder and owner, once told me. "It's what we do." Or maybe it was Rega's chairman and chief engineering honcho, Terry Bateman. Rega products are designed and manufactured in the south of England. So far as I know, no one at the Rega facility, on the Temple Farm Industrial Estate, has committed suicide; the same cannot be said of workers at the factory in China where iPods are made. Al Gore is on the board of Apple. Al, what do you think?
The dual subwoofers were bumping and our pant legs were flapping. Only moments before, we'd been treated to a polite viola da gamba. Not now. Resolution Audio's designer, Jeff Kalt, had brought only two discs with him to ensure that his company's Cantata Music Center was functioning properly in my system: Jordi Savall and Hespérion XXI's Altre Follie, 15001750 (CD, Alia Vox 9844), and Tool's 10,000 Days (CD, Tool Dissectional/Volcano 81991). After changing a few things around with the chamber music, we'd advanced to the hard rock of Tool.