[Speex-dev] Backup Echo Suppression

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Fri Jun 29 19:37:48 PDT 2007

Coffey, Michael a écrit :
> I realize that the preprocessor echo suppression is not designed
> specifically to counter the effects of data loss. On the other hand, as
> much as I might like to, I do not have the option to "fix that problem
> for real." The sad truth is that some end users have systems that may
> drop samples, or do other unfathomable things, no matter what I do. I
> can not rewrite their drivers, firmware, or operating system. My job is
> to do the best I can in a difficult situation.

Actually, there's still a lot you can do. You can reduce the amount of
sample drops by playing with the priority and the amount of buffering
you do. Also, there are sometimes ways to make sure that the drops don't
change rec/play synchronisation (the key is the sync, not the lost
samples). As for how the residual echo suppression works, I've no idea,
you need to try.

> I initially assumed that the echo suppressor is similar to other echo
> suppressors (also called "nonlinear processors" or "loss controls").
> Those suppressors use cruder algorithms that exhibit artifacts but that
> may not depend on the fine time structure of the audio signals. Is this
> not true of the preprocessor echo suppressor?

Not sure what other echo suppressors do. Some are actually designed to
act alone while others (like the Speex one) are designed only to
suppress the echo that was left by a first echo canceller.


> -mjc
> -----Original Message-----
> From: Jean-Marc Valin [mailto:jean-marc.valin at usherbrooke.ca] 
> Sent: Tuesday, June 26, 2007 8:49 PM
> To: Coffey, Michael
> Cc: speex-dev at xiph.org
> Subject: Re: [Speex-dev] Residual Echo Suppression by the Preprocessor
> The residual echo suppression is supposed to be working decently well
> now. However, it's not designed to counter the effects of samples being
> dropped off the soundcard. You'll just need to fix that problem for
> real.
> 	Jean-Marc

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