[wdmaudiodev] Re: Audio anomaly in Vista/Win7 WDM audio

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Fri, 9 Dec 2011 11:45:02 -0800

Mike Horgan wrote:
> What I’ve noticed is that at random times (typically 1 or 2 times in
> the 15 second file) I’ll hear a pop while the tone is  playing.  After
> the play I export the output usb data from the usb analyzer trace and
> look at the usb and data from the host using Audacity.  When I do, I
> can clearly see a discontinuity in the waveform, and the position of
> the glitch lines up perfectly in both the trace from the host and the
> usb data.  The total waveform itself is the correct length (15
> seconds).  If I zoom in on the anomaly, it looks like a dc value has
> been substituted for the sine wave.  In vista, the value always seemed
> to be zero, while  under Win7 it is sometimes zero and sometimes a
> negative value.  Since it appears in the trace from the host’s stream
> pointers, it makes me think that the host thinks something is strange
> about the play timing.
> Does anyone have any thoughts about what might cause such a glitch?

So, you're saying the data in the USB buffers already has this
discontinuity?  I started to write an essay about clock mismatch, but if
it's present in the original data, that's completely wrong.

What is the iso packet size in the alternate setting that gets selected?

Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.

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