NAA Clock Timing Improvements w/Asynchronous USB?


Can a Networked Audio Adapter (think Sonore or SOtM) improve the timing of a DAC using Asynchronous USB? These manufacturers place a lot of emphasis on their clocks...the SOtM even has an external connector to upgrade to an expensive master.  I thought the big revelation of Async USB on a DAC is that it no longer extracts clocking from the USB packet and frame timing signals and thus will use its own clock?  However, it's hard to believe that the timing improvements that these vendors brag about apply only to adaptive or synchronous USB.  These devices aren't cheap and I hear many folks raving about them.  Thx 
mikeb33
mikeb33, The only way it can improve asynchronous USB is by isolating computer noise, that might affect D/A converter clock.  In asynchronous USB scheme DAC operates on internal clock and takes data from the buffer memory.  The only thing USB does is to keep this buffer filled.  It is remotely possible that USB transfers can be affected by electrical noise, since in most cases there is no "resend", but it is rare and has nothing to do with stability of the clock.
Thanks.  So asynchronous USB doesn't see any of the rewards of an NAA's clocking?  The DACs clock determines the timing to a memory buffer.
mikeb33  Data is delivered from the computer as "frames" at about 1kHz rate.  Each frame contains bunch of samples.  DAC places samples from each frame into internal DAC's buffer and takes data back in order when needed for D/A conversion at the internal DAC clock rate.  Since things are not synchronized it is necessary to keep some data in the buffer.  Sending too many samples would fill up the buffer (overflow) and next incoming samples could get lost.  When buffer is empty DAC has no data to use (underflow). DAC sends back signal "DAC under/overflow".  When underflow computer increases size of the frame until it gets overflow signal.  That way computer can keep in sync amount of data being transferred, while clocks are completely independent.
Outstanding!  Thanks for taking the time.
+1 kijanki! Best explanation I've read so far on USB/DAC compatibility!
Roberjerman, thank you.   I found interesting website that is great primer on technical aspects of audio:

http://www.thewelltemperedcomputer.com/KB/USB.html