[wdmaudiodev] Audio AGC?

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Wed, 19 Dec 2012 14:34:42 -0800

I have an AVStream virtual audio driver, based originally on the
"avsamp" sample but almost completely rewritten.  I serve exactly one
format at a time, usually 22050-M-16.  The only properties I support are
the two jack descriptors.  If I connect directly to the device in
graphedt under the "WDM Streaming Capture Devices" category, audio plays
fine.  But if I build a graph using the instance under "Audio Capture
Sources", it appears that the system audio engine gets involved.  One
minor side effect is that the pin always says 44100-S-16, even though I
don't support that format.  The audio does play, however (so someone is

The larger problem, however, is that my audio is being boosted to the
point of distortion.  I don't understand where this is coming from.  I'm
currently attenuating my own signal by 50%, and the resulting stream is
still painfully overdriven.

Where is this coming from?  Is there some AGC in the audio system?  Does
it sample a short period to decide what my average volume is and boost
to compensate?  How can I stop this?

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

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