|The New Frontier: High End Computer Audio, and USB DACs|
|Home Theater Feature Articles Audio Related Articles|
|Written by Andre Marc|
|Wednesday, 02 March 2011|
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There are also several places to purchase CD quality or high resolution music via download. HDtracks.com offers a variety of options with a varied musical menu that includes John Coltrane, Paul McCartney, Robert Plant & Alison Krauss, and hundreds more. Some of these titles are available in 96 khz 24 bit resolution. Rhino.com also offers CD quality downloads in FLAC. Some artists allow for direct downloads from their own websites, including some major acts like U2, who own their master tapes.
Another method one can use is have iTunes stream music via WiFi from your hard drive to an Apple Airport Express, then connect via mini optical output to your DAC. You can use an iPod Touch/iPhone as a remote control. This method is claimed to be more sonically compromised due to the use of WiFi, and its limited bandwidth, which means no high resolution files. But many swear by it for casual listening. Apple also recently released their AirPlay app which allows enabled devices to stream music directly from an iPod Touch, iPhone, or iPad.
Now we come to what Audiophiles consider to be the optimal way to configure computer audio. That involves several links in the chain which includes a computer and peripherals, external hard drives, a USB DAC, and playback software. But there is much more to it than that. First, purists strongly prefer Apple computers, due to the way they handle audio in comparison to Windows based machines. Secondly, a noiseless, solid state internal drive is recommended. This is because music files should be stored on an external Firewire connected drive so as to reserve the use of USB resources for the DAC.
And here we arrive at the center piece of this type of setup. USB connections for audio were said to be sub par due to issues with jitter and more. But with the advent of asynchronous USB, which allows the DAC not be slaved to the computer, relieving the computer of much of its duties. Asynchronous means that the DAC controls the flow of information and has fixed oscillators for the Master Clocks. There are two methods of async protocol. There is device driver oriented custom and then there is USB.org standard asynchronous USB audio protocol. The later is included in both Windows, Linux and OSX operating systems and therefore does not require any device drivers to be written. (FOOTNOTE 1)
All of this allows for sound quality that finally rivals, or if one listens to the pioneers in this field, surpasses S/PDIF digital connections. One such pioneer is Gordon Rankin, of Wavelength Audio,(www.wavelengthaudio.com), the writer of Streamlength code, the most widely recognized and lauded asynchronous USB code available. Rankin offers a variety of DACs, and licenses his code to several notable clients, including Ayre Acousics, for their QB9 USB DAC, (www.ayreacousics.com). I strongly suggest visiting Rankin's dedicated computer audio site, www.usbdacs.com. It is probably as complete an overview on setup and and related technologies as you will find.
Other highly regarded USB DACs on the market include the DAC1 and DAC2 from Wyred4Sound, the Arcam rDac, which by all accounts is a tremendous bargain considering the price, $499. The rDac licenses proprietary asynchronous technology from dCS, another pioneer in digital sound. dCS also offer several DACs with USB inputs, but with the cheapest being around $11,000, it will probably be out most of our leagues. Empirical Audio has an entire family of USB DACs and more. The Benchmark DAC1 USB is also highly regarded. Although they may not use asynchronous technology per se, they also claim to have proprietary technology that eliminates jitter and allows all the inputs on their units to perform equally well.
There are other considerations. On the hardware side, the USB cable is of considerable importance according to many. Length should be kept to a minimum. Playback software is important, especially if one has a large collection of high resolution music. Many use iTunes as their cataloging and playback software. Some claim that iTunes is sub optimal, and their are several superior choices. Amarra, by Sonic Studios, is widely accepted as being one of the best. There are two versions, depending on your needs. Pure Music, by Channel D software, is also very highly regarded, and much less expensive Both packages work in conjunction with iTunes, but can also work stand alone. Decibel, formerly AyreWave, is currently free. Others include Audirvana, and Fidelia, both for MAC.
Now you have all your music ripped to hard drives, backed up, and connected to your audio system via the analog outputs of your USB DAC. You now can call up your music via your keyboard, mouse, and monitor, if not using a laptop, or you can use your Apple iPod Touch or iPad to scroll through, play, pause, or skip through albums and tracks. A big selling point here is being able to search your entire library, view artwork, and compile playlists on the fly.
There is an alternate way to route music from your computer to your hifi, and that is via a USB to S/PDIF bridge. This allows you to take the USB output from your computer or laptop and convert it to a S/PDIF digital output, which can then be used with your existing, non USB outfitted legacy DAC. This is a good, cost effective way to test the waters. The Halide Design Bridge, the Stello U2 by April Music, and products by Bel Canto, Wavelength, Empirical Audio, and several others are great examples. There are also a several products with analog outputs, with the DAC chips built in. Probably the best example of a highly regarded and well reviewed product in this category is the HRT Music Streamer, I can say for sure that the HRT and Halide Designs units use asynchronous technology, with HRT being proprietary, and Halide Design licensing Gordon Rankin’s Streamlength code.