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Positive Feedback ISSUE41
Ten Questions about Computer Audio with Charles Hansen of Ayre Acoustics
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.?
a) USB - There are a ton of USB DACs out there that suck. The problem is that Burr-Brown released a bunch of cheap chips that had both a DAC and USB support. (Some also have a digital out, as used in the Wadia dock.) They are super easy to use and require no programming. But they have two problems. The first is that they are limited to a max resolution of 48/16. The second is that the jitter performance is HORRIBLE. We are talking literally 100x worse than a good one-box CD player.
There is another chip from Burr-Brown called the TAS1020B. It is programmable, but it is super hard to do so. Only two people have done it in audio to my knowledge. There is a third-party developer called Centrance that has written code for the device that allows it to go up to 96/24.
But the best way to do USB is what is called "asynchronous" mode. This means that the master audio clock is in the DAC box instead of the computer. This is the only way to get jitter performance as low as a good one-box player. Gordon Rankin of Wavelength wrote the code for the TAS1020B to do this, and we are licensing it from him. dCS also has some new add-on boxes for their big stacks of boxes that uses "asynchronous" mode. Everything else is seriously flawed by comparison.
Using an SRC chip to reduce jitter is somewhat controversial from a sonic standpoint. (They tend to measure well enough.) Basically, what they do is throw away all of the original data and calculate new data that is their best guess as to what the data would have been if there hadn't been any jitter. The "best guess" refers to the algorithm used. The latest ones measure extremely well, but still haven't convinced everyone from a sonic standpoint.
b) Firewire can be as good as "asynchronous" USB if it is done right. But it requires custom drivers for each operating system. Also most computers don't support Firewire. Even Apple is dropping it in many of their products, and it will probably go away, much like DAT went away over time.
But Firewire currently has one advantage over USB. It will go all the way to 192/24 instead of just 96/24. The limitation with USB is that the TAS1020B chip is only USB 1.1, and USB 2.0 is required to get to 192/24. (USB 1.1 could do 196/20, but I don't think that there are any music player applications that will do that.)
This limitation should go away in the next year. Gordon Rankin is a smart guy and he is working on a way to get USB 2.0 working with the "asynchronous" mode. I don't think we'll have to wait too long. That will be the final nail in the coffin for Firewire.
c) Optical and Toslink are the same thing. They are optical versions of S/PDIF and require a soundcard. The only good thing about Toslink is that it isolates all of the RFI inside your computer from your audio system. But S/PDIF has the clock in the wrong place—the transport (computer) and so unavoidably adds jitter. We at Ayre have never made an external DAC box (until our new USB DAC) because of this. Some people have developed band-aids that vary in their effectiveness. For example, the Wadia ClockLink (copied from the old Linn Karik/Numerik) sends a clock from the DAC back upstream to the transport with a separate cable. It performs well but is not compatible with anything else.
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 don't know much about this, but I do know that there are issues in getting the bits out correctly. For example, when you listen to your computer for music, you also want to hear the "ding" that tells you that you have new mail. So all the sounds go through a mixer (at least in the default configuration for Windows) in order to combine all of the various audio signals. But the mixer can screw things up by changing the sample rate and adjusting the volume.
However, it's not that hard for a computer-savvy guy to get this all sorted out for a Windows box. It is much easier on a Mac. Once this basic stuff is handled, I have no idea why any software package would sound different (or better) than another. But I'm sure that it's possible. Everything makes a difference. Sometimes it can be very hard to figure out why.
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?
EAC started this whole myth about "bit perfect" ripping. The biggest problem is that if you are trying to rip at 52x, you are prone to errors compared to ripping more slowly or just playing the disc in real time on a stand-alone CD player.
So EAC came up with a way to try and fix this. There are two problems with it. It slows things down drastically, so you are probably better off just using some other program and setting it to rip at 4x or something like that. The other problem is that it isn't any better at handling damaged discs. If there is a scratch, some programs will let the drive guess (interpolate) at what the data is. But EAC isn't magic—it can't repair a damaged disc. It has to rely on some algorithm that often isn't any better than the guess (interpolation). That's why now there are these massive online databases where you can compare the checksum value of the rip you got from EAC with everybody else's. When a majority of people get the same checksum, they decide that is the real "bit perfect" rip. But unless your disc is badly damaged you get that from any stand alone CD player anyway....
One last thing. If you read up on ripping at various computer forums and websites, they will talk about "jitter" when ripping. You have to understand that their "jitter" is NOT the same as our "jitter". It's all too easy to get confused by this terminology.
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?
This belongs in the "green pen" area. We know that differences exist. We can make hand-waving explanations as to why, but as far as I know, nobody has the "real" answer. Most of high end audio is like that. For example, why do cables sound different? I mean really sound different? Nobody knows, they just make up plausible sounding stories.
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?
No clues here. All I can say is that if anybody, high end or pro is building a better DAC than our forthcoming QB-9 USB DAC, I salute them. I know what goes into our product, and it is really, really good. So if someone makes something better than that, then they are doing a great job! (That is why we licensed Wavelength's "asynchronous" mode software—we recognize when someone is doing something special.)
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?
Everything matters. Obviously jitter is a huge deal. And since computer audio is relatively new, many people out there simply are not getting that part right. After that, it is pretty much the same as any digital audio product—power supplies, analog circuitry, digital filters, low jitter master clocks, DAC chips, parts quality, et cetera, et cetera. It all matters.
It is also important to provide some sort of isolation between the RFI noise of the computer and the audio system. But don't be fooled—wireless is NOT the way to do it. Wi-Fi adds an RFI generator right in your house. The RFI gets on all of the AC lines in the walls; all interconnects and speaker cables, your power cords, everything. Unplug all of the Wi-Fi from the AC power to make sure it is really "off" and your stereo will sound better. You can get your house wired for Ethernet for a few hundred bucks. It's kind of like adding a dedicated AC outlet. Then you can ditch the RFI broadcasting station that's in most houses running 24/7.
Your readers will probably also want to know that Wi-Fi operates at exactly the same frequency as a microwave oven. There are possibly going to be some long-term health issues related to turning your home into a low-level microwave oven that is always on.
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?
No single factor. See all of the above.
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?
No single factor. See all of the above.
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?
Everything always makes a difference. I'm not surprised that getting the hard drive, memory, and main processor to do less work is simply going to create less RFI and less demands on the power supply.
10. Where do you see the greatest impact to come in computer-based audio for the future?
It is still too difficult to setup and use. Right now the techno-geeks are having a ball with it. But there are too many setup issues involved for a normal person to deal with. Some companies (e.g., Sooloos) are making it easy by offering pre-packaged systems. But these are extremely expensive, and (so far) none of them are close to being state-of-the-art in sound quality. So there is a lot of room for improvement.
The other problem that we are fighting, whether it is computer-based audio or conventional sources is the horrible RFI pollution that is getting worse and worse. Everyone has cell phones, Wi-Fi, and Bluetooth gadgets. All of this stuff has an impact. And these frequencies make it difficult to deal with effectively. It's like the slime from an old sci-fi movie—it gets everywhere.
Charles Hansen is the chief designer and founder of Ayre Acoustics. For more on Charles Hansen, read this interview.
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