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The basics of PC audio

Some questions for you:

Assuming you have the PCU (in my case, a Mac Mini) near the stereo, with a USB DAC coming out of that into the preamp (or do you have it configured some other way?):

a) What does one do with the monitor--perhaps run an extra long cord and put it away from the system to keep the RF from feeding into the audio?

b) Can the CPU be placed far enough from the preamp to where RF from it won't affect the sound of the system?

c) What about using Apple AirPort Express and AirTunes and running a USB DAC out of that into the preamp; are there any advantages/disadvantages to that sonically vs. having the CPU feeding directly into the DAC?

d) Suppose you buy music from the iTunes store in MP3 form. Can it be converted to aiff or some other "lossless" format such that you'll wind up with a high quality file? Or does the fact that it was already converted to MP3 doom it to sonic mediocrity?

e) How quickly are USB DACs improving in quality? I don't want to buy a DAC and have it be obselete the next year.

I appreciate your answers.

Thanks,

Matt
descartes
herman
2,277 posts
 
Good link Steve, perhaps you could clear up a few points.

Did the Creative Audigy 2 NX turn out to be asynchronous? I am guessing not as you have chosen others to modify.

Basically the DAC has a single digital USB input. USB unlike SPDIF is bidirectional and therefore has error correction and buffering on both sides. This happens automatically so the data on the disk is identical to what is going out all the time. Also since this interface is asynchronous the clocking problems associated with SPDIF go away.

This is a quote from the Wavelength Audio website http://www.wavelengthaudio.com/usbdac.html and is in direct contradiction to the link from John Swenson in your white paper, both in terms of USB audio being bi-directional with error correction and being asynchronous. Perhaps things have changed since your paper was published but I don't think so. Since Gordon is active on other forums I have alerted him to this thread and hope to hear from both of you on this matter.

I have no axe to grind with any of this. I am just a curious DIY guy that isn't using either of your guy's stuff. I'm presently using a Scott Nixon USB DAC that I've modified a bit (coupling and filter caps) and running from batteries.

I will say I'm not as enamored with upsampling as you are and find the non-oversampled to be more organic and musical.

I'm also considering the DDDAC or at least experimenting with running parallel 1543 DACS.
audioengr
3,282 posts
 
"Did the Creative Audigy 2 NX turn out to be asynchronous? I am guessing not as you have chosen others to modify."

No. I believe it is. It was just more difficult to mod and make into a product, besides it was discontinued as all of the other decent solutions were (Edirol UA-5, Waveterminal etc..) The transit lives on and they have no plans to discontinue it. I wil not be modding them for long anyway, as I have my own design ready to go. It will still use the M-Audio drivers and ASIO as they sound the best for PC IMO. The only upsampler that I use is Secret Rabbit Code, which I have licensed. It is better than 44.1 every time I try it.

As for the quote above, I suggest that John Swenson and Gordon resolve this. They both know more than I do about USB interfaces.

I was impressed with the Lavry DAC technology. HAve not heard one yet though...

Steve N.
herman
2,277 posts
 
Thanks Steve. I sent a note to Gordon and I'll try to contact Swenson, but everything I've read points to Swenson being correct.

I think the best solution is a wireless USB device server feeding a USB DAC. That way you aren't tied down to any single device like Squeezeboz or Airport and it's associated software so you can use any USB DAC you choose. The problem is that even though
wireless USB device servers exist, at this time there are none that can handle the isosynchronous data stream. Silex tells me that they hope to have one later this year so I am waiting for that.
audioengr
3,282 posts
 
For those that want wireless USB (the best), Belkin has announced the CableFree USB hub and dongle, which replaces wired USB with Ultrawideband, high-bandwith wireless USB. The dongle plugs into your computer or laptop and the hub goes next you your USB converter or USB DAC and uses a short USB cable. Replaces USB 2.0. Demonstrated at 2006 CES in Jan.. Latest is that they are shipping in July. Pricing expected to be under $150.00. The advantage is that you can use ANY player software with this, unlike iTunes for AirPort Express or SlimServer for Squeezebox, and it will pass 24/96!!!
wavelength
3 posts
 
Matt, there is no RFI unless you have really susceptable front end. It is best to connect the dac directly to the MAC. You cannot recover information that is in ACC so why convert it. Upsamplers and such suck the life out of music. Most AAC sound pretty good, not as good as Lossless but who cares. Sometimes you just need to listen and have fun and not get so tied up in the details.

As I see it the dacs at 44/16 will be here for a long time. The next logical conclusion will be lossless downloads. We are pretty far away from high definition PC audio as loading those files would be at least 4x the space.

Thanks
Gordon
FYI I doudt I will be back here, email me if you have questions. I have the answers.
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