Computer Audio Asylum

RE: But John that is USB jitter which we do not care about

216.196.208.221

In Reply to: RE: But John that is USB jitter which we do not care about posted by John Swenson on February 25, 2008 at 12:05:10

John,

Basically the way the PCM270x works is that it links the Spact to the SOF frame. Now since the SOF frame has no acknowlegments to it. There is also a VSOF (virtual) timer in the PCM part in case the real SOF frame is missed. The problem is the VSOF timer will always fire after the expected SOF. Which actually throws off the Spact unit, because now the expected SOF time differential is lost.

I have seen on allot of ocasions especially with my crappy HUSH pc that SOF frames are the first to corrupt for some reason and maybe this will lead to what you are saying.

Or maybe this has nothing to do with Jitter on the USB link at all.

I did some really in depth testing with ASYNC mode running 1KHz sine wave from the MAC (Faber Acoustics Signal Suite 2) to the emulator running on the TAS1020 board. In a 24 hour period running at 44.1/16 I did not recieve any packet errors.

This of course would have the same effect on any Adaptive part not only the PCM270x series.

Only packet errors would effect ASYNC mode.

Thanks
Gordon
J. Gordon Rankin

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