[wdmaudiodev] Audio anomaly in Vista/Win7 WDM audio

  • From: Mike Horgan <mhorgan@xxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Fri, 9 Dec 2011 11:10:56 -0800

I am testing an AVStream mini driver for a usb audio device and am noticing an 
anomaly.  I am using iTunes to play a 15 second sine wave, with my device as 
the default sound device.  The wave file is a one channel, 16 bit, 44100 tone.  
The connection to my pin gets established as 2 channel, 24 bit, 44100.  I am 
using a usb analyzer to capture the usb traffic and I've also modified my pin 
so that all the data from the stream pointers gets written to disk.  I do this 
in order to compare the audio data from the bus to the data from the host as 
I've been chasing this issue.

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?

mike

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