[wdmaudiodev] Re: Audio AGC?

  • From: Matthew van Eerde <Matthew.van.Eerde@xxxxxxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Wed, 19 Dec 2012 22:40:23 +0000

What version of Windows are you running on?

See the chart here: 

From: wdmaudiodev-bounce@xxxxxxxxxxxxx 
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Tim Roberts
Sent: Wednesday, December 19, 2012 2:35 PM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Audio AGC?

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 converting).

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 

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<mailto:timr@xxxxxxxxx>

Providenza & Boekelheide, Inc.

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