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.

Furutech GT-40 USB DAC
Furutech GT-40 USB DAC

A revolution is happening in the world of hi-fi—one that, contrary to the other audio upheavals of the last 30 years, combines technological innovation and better sound quality.

Fred Kaplan Fred Kaplan
Fred Kaplan, Slate's "War Stories" columnist, also reviews high-end audio equipment for Stereophile and writes a jazz blog on the magazine's Web site. His latest book, 1959: The Year Everything Changed, is in paperback. He can be reached at war_stories@hotmail.com.

In the 1980s, the warm, dynamic sound of vinyl LPs was displaced by the cold, compressed compact disc. Then, in the '90s, just when CDs and CD players were finally starting to sound lifelike, along came MP3 and iTunes, which, for all their miraculous portability, didn't even pretend to sound good.

But now, a decade into the new century, comes a set of devices that matches the convenience of new-media downloads and exceeds the sonic standards of CDs.

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This new technology is stirring great excitement among high-end audiophiles, but it's almost completely unknown outside that realm, even among the tech-savvy. It's a fair bet this situation will change soon.

The devices are called USB-DACs (pronounced "dacks")—digital-to-analog converters with a USB input and standard stereo outputs. Connect your laptop, using one of its USB ports, to the DAC's input. Run a stereo pair of standard cables from the DAC's outputs to your receiver or amp. And your streamed music (from iTunes or some other music-server software) will come wafting out of your home stereo system's speakers. You can do this already using various cables and converters. But here's the new thing: Using these DACs, the music sounds better than you've ever heard computer-downloaded music sounding. And if you download the music files in a certain way (more about this later), it sounds as good as, or better than, compact discs.

More alluring still, several of these USB-DACs are cheap. One, manufactured by a California-based company called High Resolution Technologies, costs just $150 (and it's very good).

Let's back up for a moment. Why does music from computers sound bad? It's not just the tiny, tinny speakers. Lots of people have desktop speakers, and some of them are pretty good. Still, compared with even just an adequate home stereo system, the sound is pretty drab, for two reasons.

First, the audio circuits inside the typical computer—its own tiny DACs, its analog chips, and its amps—are terrible. With an outboard DAC, the conversion from a digital signal (0's and 1's) to analog sound waves (which your ears can hear) is handled by a device that's been manufactured to do only that, and to exacting standards. This alone should make a dramatic difference. But there's another factor as well.

The second reason music from computers sounds terrible is that the most common download formats, such as MP3, compress the signal horribly. A little math (just a little) tells just how horribly.

Digital audio encodes a sound wave as a series of 0's and 1's and samples it many times per second. Each 0 or 1 is called a bit; the longer the series of bits, and the more times each bit is sampled, the richer and more detailed the sound.

For a compact disc, each slice of sound is encoded as 16 bits and sampled 44,100 times per second. So the music flows at 1,411 kilobits per second. By comparison, MP3 produces music at 128 kilobits per second—less than one-tenth the information. (Improved versions of MP3 offer rates of 320 kb/s, but that's still less than one-quarter the refinement of CDs.)

There's a reason for this: The greater the compression, the more songs you can fit on your laptop or iPod. There is a tradeoff in quality and quantity. A three-minute song, wrung through the MP3's standard compression, takes up just 2.82 megabytes on your computer. The same three-minute song, passed through uncompressed CD-quality processing, takes up 30.3 megabytes.

So before going any further, take note: If all you want to do is listen to music on your computer or your iPod, MP3 and iTunes are good enough. If you want, at least sometimes, to hear it on your home stereo, and to have it sound good (deeper bass, higher treble, truer tones, more dynamics), read on.

Even if you want to stick with MP3 and iTunes, the USB-DACs will make the music sound better on your home stereo, for the reasons stated above.

But you can also adjust the settings on your computer so that it downloads iTunes songs (and other music files) at higher bit and sampling rates. Again, if you want to listen to this music only on your computer or iPod, this won't matter much; but if you want to stream it to your home stereo, this step alone will make a big difference. (If you're thinking of downloading music at higher bit and sampling rates, you may need to buy an external storage device to hold the extra data. They're cheap these days: about $100 for something that holds a terabyte of data.)

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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