Hi - I recently designed:

http://www.core-sound.com/HeadLine/1.php

and the #1 reason we didn't include USB is the lack of a USB sound chip 
for anything above 16bit/48khz.  You'll have to write your own firmware, 
and I'm not sure you can guarantee bit-for-bit accuracy with the USB 
audio class drivers in Windows.

Also, quite frankly unless you have access to an Audio Precision or 
comparable test gear it is very unlikely you'll be able to get close to 
the DACs specs.  Performance analog design is a bit of a world unto 
itself, and you absolutely must have test equipment to check your work. 
  Things like ... the quality of the capacitors on the spdif receiver 
PLL which affects jitter which affects the DAC.  Blinking a LED causing 
a dc/dc converter to shift frequency slightly inducing noise in the 
audio band, even with converter running at 300Khz and a few inches away 
on a 4-layer board with separate grounds.  These things are solvable but 
you won't be able to objectively tackle them without suitable test gear.

But, it is a fun project!  If it isn't for commercialization the above 
doesn't matter.

J



Sean Schouten wrote:
> Fellow Pic-listers,
> 
> I am on a mission to build my self a black box DAC based on the AD1955 DAC
> (the specs are real sweet btw!) paired with some AD797 OP-AMPS (also real
> sweet!). I want this Blackbox to have both high quality SPDIF and USB inputs
> that support up to 192Khz sampling rates a-la 24-bit sound. My problem is
> that I can't seem to find an USB-I2S IC that supports datarates of over
> 48Khz, which is a problem I am not experiencing with the SPDIF side of the
> story.
> 
> Does anyone know of an USB sound chip that supports 24-bit sound with up to
> 192Khz sample rates? Google is making me dizzy!
> 
> Yours truly,
> 
> Sean.
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