USB-DACs: The new devices that make downloaded music sound good.

Pop, jazz, and classical.
Dec. 27 2010 10:03 AM

Dulcet Downloads

Tired of crummy MP3 sound? A new device will make your digital music truly sing.

(Continued from Page 1)

A few companies out there are selling music-downloads at bit and sampling rates that exceed even those of CDs. One such company, called HDTracks, offers music at 24 bits and a sampling rate of 96,000 times per second—or, as the cognoscenti call it, "96/24." (Initially, HDTracks offered only music from audiophile labels, but in recent months it has started to lease from the catalogs of major rock, jazz, and classical labels. See their offerings here.)

At 96/24, music flows at a rate of 4.39 Megabits per second—more than three times the quality of CDs and over 33 times that of MP3.

There's another critical difference between CD sound and downloads. Inside a CD player, a laser beam tracks the pits of a disc (into which the bits have been carved, none larger than 1/10,000th of an inch wide) as the disc spins at a speed of 3.5 to 8 revolutions per second (it gets faster as the beam approaches the disc's center).


Even in very sturdy (and expensive) CD players, the beam is unavoidably exposed to a certain amount of "jitter," caused in part by mechanical vibrations, which makes the laser-tracking less than perfectly accurate. All players have "error-correction circuitry," which is designed to compensate for this jitter, but this circuitry isn't entirely accurate either.

By contrast, with downloads (96/24 or otherwise), the music simply streams from the hard drive; there are no moving parts. All other things being equal (a crucial premise), streamed music should sound more seamless and natural than music tracked on a spinning disc.

I recently compared CDs with music-downloads on my own stereo system, using a variety of formats and USB-DACs. In one experiment, David Chesky, proprietor of HDTracks, brought over a MacBook Pro laptop and an off-the-shelf DAC comparable to models that retail for about $500. He'd previously loaded the Mac with 96/24 files of recordings that I own on CD.

This was an experiment seemingly stacked against Chesky. The CD player I used was Krell Electronics' Evolution 505, which retails for $10,000. It sports a very rigid chassis and transport, state-of-the-art circuitry and power supplies, and a superb internal DAC. The Krell did sound better—it revealed more harmonic detail, deeper bass, silkier violins, snappier drums—but not by much. Sometimes we had to go back and forth, from the Krell to the Mac and back again, a few times before deciding which sounded better. The contest was very close. But the fact that it wasn't a landslide for the Krell is astonishing.

The audiophile community has caught on rapidly to these new outboard DACs. For the past year, the top high-end journals Stereophileand The Absolute Sound have published at least a couple reviews of new USB-DACs in every issue. (Note: I write for the former magazine and used to write for the latter.) Several people tell me that, at the recent Rocky Mountain Audio show in Denver, very few speaker and amplifier manufacturers were showing off their products by playing CDs; most were spinning vinyl LPs (still the preferred medium for excellent sound) or streaming from laptops or dedicated digital music servers.

This market is moving so quickly it's already in a transition stage, even before it's percolated to the broad commercial world. High-end companies that make CD players are installing USB inputs in the back of their new units, so you don't need to buy a separate DAC; you can stream data straight from your hard drive to the CD players' own internal DAC.

Meanwhile, there are downloadable software programs that allow you to bypass iTunes altogether, or to use it only as a way to organize data. One such program, which cost about $125, is Channel D's "Pure Music."

For some time, recorded music has been heading in this direction, with physical things, like CDs, likely to remain on the market, like LPs, as mainly boutique commodities. People who care about sound quality have worried about this trend, wondering if the only way to hear new music will soon be through streamed formats that are wonderfully convenient but lack the warmth and dynamics of a well-mastered disc.

Now, it looks like we might have it all.

(For a guide on how to upgrade audio settings on a Mac, click here. For how to do it on a PC, click here. For a video demonstration of how to use HDTracks, click here.)

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