[speex-dev] Re: speex_denoise on non-microphone noise (static ?)

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Fri Sep 19 20:19:18 PDT 2003

> Then I pulled the microphone out. Our system still records noise. To 
> isolate the problem, I wrote a small app just to open the device and 
> record raw samples, calls speex_denoise() and outputs both sample
> sets. 
> The noise is still there, with level fluctuating with gain level,
> unless 
> "All mute" is chosen. 

> In the case when NO microphone is plugged in, speex_denoise() smoothes
> the signal and produces smoother (and even amplifies the signal)
> speech 
> like signals. It seems that speex_denoise( ) is very sensitive to 
> static noise. 

What happens (denoiser amplifying the signal) is that there is also an
AGC (automatic gain control) that thinks that the noise is speech
(because it's the loudest signal is hears) and amplifies it to make it
sound loud enough. I completely changed the structure of that code (now
called speex_preprocess_*) and the AGC is now optional (off by default),
so it should fix your problem.


Jean-Marc Valin, M.Sc.A., ing. jr.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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