[Speex-dev] AEC Troubles

Jean-Marc Valin
Fri, 21 Aug 2009 12:48:46 -0000

Quoting Greger Burman <greger at
mobile-robotics.com>:
> I have noticed that the delay between echo signal and the microphone signal
> also has an effect on how well Speex AEC performs. I did some tests with
the
> testecho program. With the signals perfectly aligned echo cancellation was
> near perfect. When I introduced a small delay of <20 ms between speaker
> signal and microphone signal, I got no noticeable echo cancellation at all.
> I don't know if this is the expected behavior. My sample was quite
short and
> perhaps the AEC needs time to converge when there is a delay between the
> signals. The question is how long time? Jean-Marc can probably shed some
> light on that.

If the echo in the mic is *before* the speaker, then you cannot have any
cancellation. OTOH, if the echo in the mic is *after* the speaker, then the
degradation is just linked to the delay (i.e. no real degradation if the offset
is small).

> Something I am wondering about is: Should the delay between speaker signal
> and mic signal be taken into account when choosing the tail length? Or is
> the tail length independent of the delay?

Well, if you have an offset of X ms, then you should probably increase the tail
length by the same amount.

   Jean-Marc


> //Greger
> 2009/8/21 mrywhh <mrywhh at 163.com>
>
> > Hello??
> > I am a new user of speex.I am currently working on speex frames and I
have
> > some questions.
> > I am using narrowband and long tail length, and it works very well
with
> > speex test DEMO. But it is very difficult to have speaker input in
perfect
> > sync with mic input. Speex does not work at all.
> >
> > Any suggestion?
> >
> > Regards??
> >
> >
> >
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