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

What a difference a decade makes. Ten years ago downloading an MP3 file of an average length pop song would hog up tons of bandwidth and test the patience of a saint. Fast forward and today downloading  or streaming uncompressed, feature length films, full CDs, and huge graphic files are as common place as sending emails. Modern Internet bandwidth has created a new culture, one where massive file transfers, real time video, and wireless hot spots are part of daily life.

But there have been other developments that have also changed the way we go about managing our media. Data storage has become affordable, and shockingly so. A 1TB USB external hard drive can be found at most electronics stores and e-tailers like Amazon for under a $100, with prices continuing to drop due to fierce competition and innovation. Not only has storage become more affordable, but  large capacity drives are now not much bigger than a deck of cards. My first 80 GB USB external hard drive was larger than a hard cover book! Computer processors have also leaped light years ahead, and so has RAM, allowing for a much more sophisticated control center for media and communications.

What, above all else, could not be imagined ten years ago is the acceptance of the personal computer by the audiophile community as a legitimate, high end source for music.  Especially when put into the context of the recent vinyl resurgence and  the introduction of high resolution formats like DVD-A and SACD.  In digital, the optical disc was the format, and “storage” meant a  media rack on your wall.  Lastly, years ago, Ethernet and WiFi networks were confined to those with means, and businesses. Today home networks are as common as digital set top cable boxes.

I won’t go into the history of desktop computer audio, with the advent of file compression formats like WMA and mp3, as this article will focus on computers in the context of the  audiophile world. But briefly, the introduction of file sharing services like Napster and LimeWire, media players like WinAmp, Foobar, Windows Media Player, iTunes, and others, along with the coming of the iPod allowed the home computer to become a hub for acquiring music, listening to music at work, and loading up portable devices. The personal computer as media hub is also blamed for the general decline in sales and importance of physical media.

computer audio 1Audiophiles have been slower to warm up to the personal computer as an audio source for a number of reasons. First, audiophiles generally consider convenience secondary, and purity of the audio chain and sound quality paramount.  Many considered the computer ill equipped to interface with expensive, hand made components and speakers. But the introduction several years ago of hard disk based music servers aimed at audiophiles from companies like Sooloos, Qsonix, and even McIntosh and Naim, opened the doors.

As a slight detour, I must point out that computers have been used in recording studios and in pro audio for decades for live sound, recording, editing, and mastering. Comprehensive software packages and custom hardware like Pro Tools have been a reality since the demise of analog tape. So the use of computers for high fidelity playback in the home was probably inevitable, and not unprecedented. Many professional sound devices like reel to reel tape recorders, DAT machines, and even XLR cables found their way into audiophiles dens after  being used in professional environments first.

Computer Audio: The Basics:

Music files can be ripped or downloaded on to  your hard drive in a multitude of formats. WAV and AIFF are uncompressed files. FLAC (Free Lossless Audio Codec), ALAC (Apple Lossles Audio Codec), and others are considered lossless compression formats that can save a bundle of hard drive space without a decline in sound quality.  Files can be converted back and forth between formats easily with free software packages like Traders Little Helper, iTunes, MAX, xACT, and Foobar. It should be noted that iTunes does not on it’s own handle FLAC files. But some experts say it is best to rip an error free  uncompressed file to the hard drive, then convert your desired format. You can use iTunes to rip, or another software like EAC for PC, or XLD for Mac.  An internet connection is required for albums not recognized by your ripper.  With FLAC, you can save up to 50% of your storage space, with no loss of fidelity. Some claim they can hear a difference, but I find that hard to believe when considering my own comparisons.  Those who insist WAV or AIFF sounds better attribute it to the fact that there is less processor power used when decoding files. So in theory, there is a basis for this view.  

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.   

So how do sound files on your personal computer make their way to your prized high end audio system? There are a few ways. First there are devices like the Logitech Squeezebox, and others that connect to your computer via a network, either using WiFi, or hard hardwired Ethernet, interfacing with either SqueezeServer software or iTunes on a host PC to select and play back tracks. You simply either run analog interconnects out of the Squeezebox intro your preamp or integrated amplifier. Or, for much better results, you can run a digital cable out of the Squeezebox to an external DAC.  I am currently using the Squeezebox (now the available as a “Touch” version) but there many more “network players” available from companies as varied as Naim, Bryston, Marantz, Sonos, and Cambridge Audio.  One thing all these units have in common is that they are designed to not directly interface with your computer.

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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.  

usb stickThere 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.



Besides having your entire music library at your finger tips, those who strongly recommend this set up also claims that it out performs optical disc playback, even on top flight disc players and by a large margin. Technically, hard drive play back is said to reduce jitter and other anomalies introduced by the demands of a spinning disc and laser. Add to that the convenience of being able to customize playback, download music, and to set up multi room systems and you have many reasons to explore this set up. As noted, being able to, use an Apple iPod Touch or iPad as your remote control, with all library information in the palm of your hand is indeed amazing.

At many recent high end audio trade shows, computer based playback systems were very much in vogue. Many were using customized PCs or Mac computers, modified for the singular task of high quality audio. There are companies, including Mach2Muisc, that are modifying Mac Mini's. Some of the mods include removing the hard drive and putting in an external enclosure for music storage, and installing a solid state drive to run the operating system and software. They also put in at least 8GB of RAM, and load up Pure Music, or Amarra. Another relatively new development is the proliferation of USB cables produced by high end audiophile cable companies that can run as much as a hundred time the cost of generic USB cable. They claim to be made with the same exacting standards as high end analog cables. High quality connectors and conductors,  and careful attention to jitter reduction seem to be the major selling points.  On the lower end, Belkin Gold cables seem to have gotten a thumbs up from the price to performance ratio camp.

 

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Conclusion:  

For several years now, some in the mainstream press, and a chorus of high end audio journalists and designers have been talking about the demise of CD players, and disc spinners in general.  Hard drive playback is the path forward, they say. No one knows for sure, but new models of CD players seem to keep appearing every year from various high end companies, albeit some with new, cutting edge features, like digital inputs, internet connections, and even touch screen interfaces. That being said, companies known for classic, tried and true hifi gear are introducing music servers and related products. Cary Audio, Bryston, PS Audio, the previously mentioned McIntosh, Naim, and more, have come to market with hard disc, sophisticated music servers, network players, and other products designed to push the hobby into the future. Even Conrad Johnson, known for classic tube gear, now has a USB DAC, with technology licensed from HRT.

I for one am fascinated by this new direction, and will be looking to explore it in the future, when resources allow. Others have already jumped in, and the numbers will only grow.  I also think that as infrastructures are put into place, downloading CD quality and high resolution music will be the normal way to purchase media. It won’t happen tomorrow or next year, but there is no doubt that road is being paved.  To explore further, check out some of the links below and consult with your local dealer, and as mentioned above, check out www.usbdacs.com .

FOOTNOTE 1: Per Gordon Rankin, Wavelength Audio.    






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