[Speex-dev] Leaking audio and AGC/VAD

Jonas Tärnström njt at home.se
Fri Feb 3 02:42:23 PST 2006

I am working on a VOIP implementation were one of the key design goals
is zero user configuration. Similar to Skype.
What I've come to notice is that my soundcard (NForce4 based) leaks
audio from the playback path to the recording path. 
This is probably not unique for my hardware at all and will happen on
some percentage of all users of my software.
(All of this is Win32)

What happens is that when no one is talking I think Speex pre-processor
starts to think that the very quiet leak from my playback path is
actually someone talking.
I am using AGC and VAD and my guess would be that AGC amplifies the leak
to such a level that VAD starts triggering.
This is rather annoying for the user if the software is used while
playing MP3s (loud) or playing computer games.

Would it be possible to implement some sort of a threshold to limit what
Speex classifies as "usable sound" or something?

I would also like to thank the entire Speex effort for this great piece
of software and especially Jean-Marc Valin

//Regards Jonas Tärnström, Sweden.

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