[Speex-dev] AEC: Tips on signal synchronization.

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Tue Dec 29 16:51:51 PST 2009

A cross-correlation is indeed a good way to figure out the alignment. 
However, every time you have to *change* the alignment, then you lose 
all the adaptation you've done so far, so be careful.


On 2009-12-29 11:38, Marco Pierleoni wrote:
> Hello,
> I am using the speex AEC in a real time application.
> I have experienced that when the mic and the speakers tracks are on sync
> or with a small delay the AEC works very well.  I understood that when
> they are out of sync the AEC cannot works, so what the "user" should do
> is to focus in order to have the tracks on sync.
> Since I am working in an environment where it is not rare to have tracks
> out of sync, I was wondering if you can help me to find a reliable solution.
> Right now I am working on two recorded audio track where the mic and the
> speakers are both in sync or out of sync in different parts of the files.
> I am trying to perform the synchronization, using the cross-correlation,
> on each frame before to pass on the echo_cancellation.
> In particular the parameters of cancellation will be the frame taken
> from the mic file, and the frame from the speaker files which better
> cross-correlated with the mic frame.
> The result is not very different from the output without synchronization.
> So my questions are:
>   - Do you think that an approach like this could, in principle, give
> more echo cancellation? Let's forget the performance, just for now.
>   - Do you have any idea how to obtain faster re-adapting, if the tracks
> go out of sync?
>   - I read the papers cited in the code, but I cannot understand
> completely how the algorithm works and adapts; do you have any available
> references to suggest in order to have a better understanding and to try
> to obtain an echo cancellation in these bad situations?
> Thanks for your help
> Marco Pierleoni.
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