[Speex-dev] AEC - Echo is cancelled however.....

[Marco Pierleoni]

Hi Helton,

it is now several months that I am using the AEC speex. I experienced
very good performance and I agree that the synchronization is the most
important issue here. As a matter of fact I believe that your problem
could derive from a not perfect synchronization.
It seems that that filter, used in the AEC, is always adapting. When
you have not a perfect synchronization, the adapting filter allows to
cancel most of your echo, while the participant is talking. Once he
stops to talk, the filter cannot adapt in the right way until he
begins to talk again.
I think that this is the cause of the small return of echo.

I don't know the details of your application, but in my case I wanted
to play audio packets incoming from the network, and I had similar
problems until I put a jitterBuffer between the network and the audio
device. This solution allows me to have a better scheduling of the
packets sent to the audio device improving the synchronization.
You should also consider that the sound card have an own internal
buffer which can introduce some anomalies in the audio playing, like a
small pause or an audio cut. Most of these anomalies are very
difficult to be heard but they are important for the synchronization

I hope that this could help.

Marco


2010/5/10 Elston Sa <jose at rebaca.com>:
> 1) Everytime a participant speaks there is a echo for a short duration
> (maybe a word or two) but as the participant continues to speak without a
> any break the echo is 95% cancelled (i.e there is a feeble echo still
> present if observed very carefully).
> 2) The moment the participant stops / pauses speaking and start talking
> again, scenario 1 is repeated as if the echo state has been re-initialized
> or reset.
>
> Please note that I observe this in a single audio session and not after
> restarting the application. I confirm that I am not re-initializing the echo
> state after the session starts.
>
> Is this normal? Is there any way I can keep the echo state to what it was
> when the participant not speaking.
>
> Also, any pointers on why I get a feeble echo back would be greatly
> appreciated.
>
> Thanks,
>
> Elston
>
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