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

Elston Sa jose at rebaca.com
Tue May 11 00:43:01 PDT 2010


Thank you for your response.

Is there a way I can determine if the synchronization is perfect or not? If
not by how much it is off.

- Elston

-----Original Message-----
From: Marco Pierleoni [mailto:pierleoni.m at gmail.com] 
Sent: Monday, May 10, 2010 3:46 PM
To: Elston Sa
Subject: Re: [Speex-dev] AEC - Echo is cancelled however.....

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.


2010/5/10 Elston Sa <jose at rebaca.com>:
> Yes. I guessed that too, however I am not sure why it keeps repeating
> time the user stops / pauses and starts speaking again in a single
> I am using a laptop with standalone speakers. For echo cancellation to
> one has to make sure that the ref and echo buffers are synchronized. I
> this is the most common problem.
> -Elston
> -----Original Message-----
> From: Anton A. Shpakovsky [mailto:saa at tomsksoft.com]
> Sent: Monday, May 10, 2010 2:43 PM
> To: Elston Sa; speex-dev at xiph.org
> Subject: RE: [Speex-dev] AEC - Echo is cancelled however.....
> Well, AFAIK AEC engine needs time to adapt. So probably that's why at
> the beginning of the conversation
> you hear the consequences of this adaptation. Btw, what sound system do
> you have? I mean laptop or arbitrary
> acoustic system? I'd like to know, cause I couldn't get enough echo
> cancellation with speex in my environment with
> standalone speakers AT ALL.
> -----Original Message-----
> From: speex-dev-bounces at xiph.org [mailto:speex-dev-bounces at xiph.org] On
> Behalf Of Elston Sa
> Sent: Monday, May 10, 2010 3:41 PM
> To: speex-dev at xiph.org
> Subject: [Speex-dev] AEC - Echo is cancelled however.....
> 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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