Positive Feedback ISSUE 41
january/february 2009

Ten Questions about Computer Audio with Tony Lauck

Computer Audio has become the new rage in audio and for good reason: one has an easy and instant access to all their music as well the ability to search out countless other titles via the internet.  The issue is simply where to start, though the answer is quite obvious: get a computer, rip and store the files, and then play them back to some DAC. Of course being audiophiles …err the nuts we are… the questions start to pile up rather quickly.

Mac or PC, and then once you got that settled, there is all the minutiae related to just setting-up that computer’s OS and configuration. Then comes how best to rip and how best to save the files, and then to where? Okay, so now that I have my files, how best to play them back and how best to get the files out of the computer and to what DAC? Yadda, yadda, yadda… each question leads to further questions to clarify the previous that then lead to other questions that suggests another question and …a downward spiral down into the rabbit hole we go.

So I went to the 2009 CES and found not only a wealth of information, but a wealth of confusion or at the very least, a wealth of disagreement among those that are either in the recording/software side, the hardware-side, and/or the "expert" sides of computer audio. Now CES is not the best place to get all the answers… time is an issue as is finding all the people to ask, so I came up with 10 ‘key" questions (these are my 10, you may have others or perhaps might not find these of any benefit to you, but I chose them because they are of interest to me and besides they reflect the most common or important areas that seem to pop-up whenever one talks about computer-based audio, so go pound silicon if they don’t work for you.) and emailed them to 12 people in the industry to answer. Their responses are here...

1. Let's start with interfaces; the obvious choices are USB, Firewire, Optical, and S/PDIF. What is your opinion on any of these interfaces? What if any, are the advantages or disadvantages of one over the others in terms of resolution, jitter, etc.?

USB has the advantage of widespread support, as well as drivers that come with the operating system. This is a mixed bag, because there is no way to run at high sample rates using the standard drivers. Thus, it is possible to work at 96/24, but not input and output simultaneously.

It is possible to avoid transport jitter problems by running in async mode, something that is not possible with common optical and coax S/PDIF connections. I plan on moving away from USB because of the sample rate limitation.

The future of Firewire appears suspect. I haven't investigated its properties in any detail for this reason.

My past experience with optical interconnects is that they suffer from jitter problems and that coax works better. This is supported by theory, as well.

S/PDIF is poorly designed. Either a separate clock line should have been used, or (better) the system should have been designed so that the transport can be slaved to the DAC. (Some equipment supports this, e.g. some Prosumer gear.)

I think the best present approach for consumer playback is to use a LAN based interface, with the DAC requesting packets from the server. This should make it possible to achieve physical, electrical and logical isolation. Unfortunately, existing products of this sort are either limited in sample rates (e.g. Squeezbox) or absurdly expensive. (Linn)

2. With regards to software there are also strong opinions as to some being vastly superior (or for that matter, inferior) to others; people clearly hear differences in how files are being played back and therefore prefer one over the others. There is also a growing opinion that Pro software is the only way to go and that using iTunes, WMP, MAX, or other free software playback programs (FooBar, JRiver, MAX, etc.) is not the way to go. That is, these are sonically and musically inferior to the Pro software because the Pro software (say for example Amarra, Izotpe, etc.) is simply "better" at playing back music files. What is your opinion on what is going on here? That is, why would any of these programs be superior—or for that matter, inferior—to another with respect to say a .wav file in any resolution: 16/44.1, 24/96, or 24/192? Is it a matter of timing and jitter? Issues with the operating software and processing? The fact that some software runs "cleaner" than others—that there is nothing running in the background to muck things up? Or as some suggest that the "math" is simply better in some software than in others?

I use cPlay. This has a very good sample rate converter. It is very low profile and uses less processor resources. This is the likely reason why it sounds better than FooBar which I also use on occasion. I also use pro-software such as Sony SoundForge. This sounds about the same as cPlay, but it does not perform real time sample rate conversion.

If no up sampling is being performed, there is no "math" involved and I have verified that Foobar, SoundForge and cPlay all send the same bits to the sound card driver. In any event, I use a 24 bit DAC and am not particularly bothered by imperfections in the low order bit. Those who worry about such things are either foolish or are using 16 bit DACs, which in my opinion are obsolete (when used at 44kHz).

There are audible mathematical differences in sample rate converters and dither software. There are even bugs in some SRC software. This can be verified by looking at spectrum analysis of test waveforms.

3. Let's move on to ripping. As with the above, there are proponents that claim only certain software, and optical drives for that matter, can "accurately" rip a CD. That they can clearly hear differences between rips via different means; even though the rips are bit for bit perfect. Any thoughts on what is going on here? Is there an advantage to using specific ripping software or drives over another? Say iTunes, WMP, Max or whatever when compared to say EAC?

The majority of discs can be accurately ripped with ordinary drives without any errors. Unfortunately, my experience is that a minority of discs will have errors and these will sometimes be audible. (Perhaps a few percent of discs.) For that reason, I use EAC. While it is not as fast as other methods, it is not necessary to worry about whether a rip was good or not.

If insecure methods of ripping are used then there is a problem: If error correction is turned off then one can easily tell by listening whether a rip was good or not, but then many otherwise good rips will be bad. On the other hand, if error correction is turned on, then it is unlikely that there will be data errors unless a CD is defective or badly damaged. However, if there are data errors, C2 correction is invoked and they will be "concealed". This results in small sonic degradations that may be difficult to hear. Either way, one worries unless one uses a secure ripping process. EAC meets my needs, because it tells me whether a rip had errors or not. This is more important than getting the fastest possible rips, as I can do other things while waiting for my rips to complete. 

4. File formats. Any reason why a .wav, AIFF, or FLAC file is better than say Apple Lossless? Again people suggest a strong preference for one over the others, so something must be going on here?

.wav has no standard method of tagging, and this makes it less useful for people with large collections of material. AIFF is not common in the PC world, so I don't normally use it. Although similar in most respects to .wav, AIFF does have standardized support of tagging.

FLAC files support tagging and the format supports all PCM formats commonly used. The encoding is definitely lossless. (There is one problem that I have observed, 24 bit FLAC files created with new versions of FLAC don't play with software using outdated versions of FLAC. Other than this one problem, FLAC has been completely reliable as I have used it.)

Apple Lossless on the PC does not support 24 bit PCM. For 16 bit material it appears to work OK, as does Windows Media Lossless. (I have not tested WMA lossless with 24 bit material.) I don't normally use these formats because they are proprietary and not supported by cPlay. I have some WMAlossless files from several years ago and before listening to them I use dBPower amp to convert them.

With some equipment, real-time decoding of lossless formats may impact playback quality, even though there are no arithmetic errors. There is good evidence that this is caused by the timing of processing load and its electrical effect on transport clocks, eventually resulting in jitter in the DAC clock. I use cPlay, which decodes FLAC prior to music playback. Therefore this is not be a factor in my usage. I prefer to use FLAC for its support of tagging, and its conservation of disk space. A secondary benefit of reducing disk space is that backups take less time.

5. There is also a movement towards Pro DACs. Naturally there are DACs of varying quality and performance, but is there any reason why a PRO DAC would be better than a DAC made by a manufacturer from the audio community? Say ones of comparable quality and build?

There are different segments of both markets, so I don't believe there is a general answer. If one wants the latest audiophile fad, one will probably not find it among pro audio products. I have no reason to believe that the best sound quality can't be had from either source. If one is interested in price/performance that's another matter and I don't have any opinion.

6. Along those same lines, what makes one DAC a better choice for computer-based audio than another? Jitter reduction, chip sets, power supply, etc?

I don't have sufficient practical experience to answer this. If forced to guess, I would list in likely order of importance: power supplies, jitter reduction, and chip sets.

7. What do you see as being the most important factor in getting the best sound in computer-based audio? That is what should the consumer address with the greatest concern when setting up a computer-based audio system?

Understanding what is going on with the hardware and software. Without this understanding, one is flying blind and subject to luck.

8. Along with that, what do you see as being the most important factor in NOT getting the best sound in computer-based audio? That is, what can have the greatest potential to adversely affect the sound in computer-based audio?

Glitches and interruptions from extraneous activity in the computer system. The worst offender is anti-virus software. But there are many other system processes that can cause problems. Others I have found are things that hang around after applications have been closed, such as "iTunes Helper" and "iPod Service".

Next in line are operating system converters and mixers, which are not transparent to sound quality. These can be bypassed by appropriate interfaces, such as kernel streaming or ASIO.

After that comes general cleanliness of power and signals, as affected by hardware and software in the box.

9. Some suggest that they computer must be audio dedicated. That is it must be "built" or configured for the specific purpose of only playing music and that any and all non-audio related programs and such must be eliminated. Your feelings on this? Is it important or not, and why so?

For the very best possible results, simpler is better, if only because there are less places that have to be examined when dissatisfied. I dedicate my machine to audio only, but this includes making digital transfers from analog tape recordings and performing audio editing functions. On occasion, I do use this machine to download audio files from Internet sites. However, when I am doing any critical work I do not run any unnecessary software and I first reboot the machine.

I would prefer this would not be the case. It is due to the poor design and implementation of interfaces that things going on in the transport other then moving the correct bits can affect the sound quality output by a DAC. In my opinion, the proper way to address these issues is through better interfaces or DACs that have better isolation. Dedicated, or quasi-dedicated PCs are merely expedient stopgaps.

10. Where do you see the greatest impact to come in computer-based audio for the future?

Network interfaces that run at very high sample rates, possibly even higher than 192kHz. These should meet the goal of sonic independence from computer system artifacts.

Tony Lauck is a frequent contributor to to Audio Asylum's Computer Audio message board. He is also a consultant in computer network architecture and technology. Tony maintains several web sites and digitally re-masters and restores cassette and open reel recordings.

From Tony:

My introduction to audio began as as teenager in the 1950's when I helped my Uncle build and tweak a Dyanaco amplifier. This project included building test equipment and learning how to use it, tweaking components in the feedback loop, watching the plates glow red, and eventually getting good sound. A few years later I went to high school where I met Brad Meyer who introduced me to stereo. In this period I used to lug my Bell tape recorder, Dynaco PAS-2, Citation II and KLH-6s to a large auditorium where J. Peter Moncrief and I used to play our prerecorded tapes.

While I was at college supposedly studying mathematics I worked at the radio station (WHRB) where I met Clark Johnsen. My work there was as a studio engineer and a programmer of classical music. On one occasion I got to make a live broadcast and recording of the Boston Symphony Orchestra.

When digital audio came along, I got caught in the cross-fire between the pro's (e.g. Brad Meyer) and the anti's (e.g. Clark Johnsen). Both Brad and Clark had been roommates one summer while we were in college, and I was disconcerted when I learned of the conflict that had arisen between them. I took it upon myself to find out who was right, but there never was a satisfactory resolution of this matter. I ended up spending a lot of money on audio equipment over the years attempting to get to the bottom of this question. Fortunately, this investment provided many hours of musical enjoyment although the initial quest was never satisfied.

For 30 + years I worked in the computer industry, most of the time for Digital Equipment Corporation, where I was a Corporate Consulting Engineer and the Technical Director of Networking. I contributed to the design and standardization of network architectures and protocols, as well as hardware and software associated with computer networking. I supervised a group of computer scientists and advanced development engineers. Whenever I encountered a technology of interest I made a point of learning about it, so that I could be an effective technical leader and mentor. (This is how I came to learn about Information Theory and Digital Signal Processing.)

A few years ago, a friend with a small record label and web site asked for some help digitizing analog recordings for archival purposes. This led into re-mastering some of these recordings for CD and, more recently as downloading on the web site. (www.innersong.com). Doing this was not as simple as I thought it would be when I began. There were many gotchas associated with PC audio that I had to bypass before I could get consistently good sound out of an inexpensive PC based system.

I enjoy listening to classical music on my PC based system, including hundreds of CDs that I have ripped and about 100 high resolution downloads that I have recently purchased.

www.aglauck.com

Use the links below to read other responses to these questions

Larry Moore and Eric Hider of Ultra Fi Audio Designs

Andreas Koch of Playback Designs

Tony Lauck

Steve Nugent of Empirical Audio

Gordon Rankin of Wavelength Audio

Jon Reichbach of Sonic Studio/Amarra

Vinnie Rossi of Red Wine Audio

John Stronczer of Bel Canto Designs

Daniel Weiss of Weiss Digital Audio

Vincent Sanders and John Hughes of VRS Audio Solutions

Kent Poon of Design w Sound

Charles Hansen of Ayre Acoustics

Pete Davey of Positive Feedback Online