[speex-dev] speex preprocess redux

Tom Grandgent tgrand at canvaslink.com
Mon May 17 16:51:31 PDT 2004

I'm not sure if this is due to the same problem, but I get the 
same clipping behavior when trying to use VAD+denoiser on a 
particular mic+speaker setup that has significant background noise 
(enough to really foul up the codec should the denoiser be turned 
off.)  Leaving VAD off and transmitting continuously seems to be 
the only way to avoid this clipping.

Another person I regularly communicate with also has a mic+speaker 
setup but not much background noise.  With VAD+denoiser enabled, 
I never have any trouble hearing him.

This gives me the impression that VAD doesn't function too well 
when the input is noisy, even if the denoiser can do an excellent 
job of cleaning up the signal.  So it seems that VAD is being 
done before denoising, and looking at the code for 
speex_preprocess(), I think this is the case.  (Am I wrong?)

Why not do VAD after denoising?  It seems like it would be much 
more reliable.


Tom Harper (tharper at sightspeed.com) wrote:
> Steve,
> The main problem I am having with the system is clipping off the start
> of someone's speech when they first start talking- the ends of the sentences
> seem to be handled properly.  I am wondering whether this is the fault of the
> audio playback system or whether this is a speex issue-
> I also get the musical artifacts problem with the denoiser.  This seems to
> be more of a problem on open air mics/speaker combinations.  However,
> this and the issues you pointed out are a minor deal in comparison with the
> clipping problem.
> Tom

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