[Speex-dev] Echo cancel

Ard van Breemen ard
Fri Jul 16 01:40:29 PDT 2004

<0I0W00GUFF02LV at tid.hi.inet>
Message-ID: <20040716084029.GA1732 at kwaak.net>

On Thu, Jul 15, 2004 at 04:55:42PM +0200, Gustavo Garc?a Bernardo wrote:
> Somebody has tested succesfully the speex echo cancellator? Sometimes ago I
> post the same question, and it was very untested.
> Best regards, and thank you very much for your work.

With a lot of fiddling and some good hints from jean-marc, I
actually got good reasonable good cancellation.
One of the biggest problem I had was that the dial-tone somehow
influenced the adaption-process that it continued singing along
for more than 30 seconds. By stopping the adaption process at the
moment that nothing comes into the mic (I am cancelling the echo
from the telephone line connected to the modem), it was greatly
Second improvement was using auto-gain to get a constant "volume"
that needs to be cancelled.
Third "improvement" was slowing down the adaption process.
Fourth "improvement" was adding "comfort noise" to give the users
a base noise to focus on. Without this noise, users tend to
increase the headset volume, which increases the amount of
feedback they hear, which makes them want to increase the volume
to hear the other side better, etc...
The problem (what I've noticed) is that the user is extremely
perceptive for his own voice, so it really needs to be tuned down
a lot.
BTW: I tend to increase the volume of the incoming signal by 2,
and divide the echosignal by 10 before I fed it into the
echocancel process.
(Still need to put this sofware on a webserver though... :-( )

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