[Speex-dev] AEC in speex

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Mon Sep 5 16:04:04 PDT 2005

> 1.After the error values are computated in teh daptation process a check -if
> filter is completely mis-adapted - is performed. How could you explain the
> criteria used for this check.

Sure, I check the correlation between what I remove and what's left
after. If that correlation is far in the negative, it means I'm actually
adding more echo instead of removing it.

> 2.what exactly is meant by  over-cancellation and under-cancellation ?

This is a bit similar to point 1. I check whether I'd get better results
be multiplying what I remove by a certain factor. If I'm removing too
much (hence adding some echo with opposite phase), then it's
over-cancellation, if I'm not removing enough, then it's

> 3.Also it was seen that without the speex_preprocess call the output quality
> is very much differnt. Is this expected ? if yes will this not increase the
> complexity of operation considerably ?

Yes, the preprocessor is able to remove a lot of the residual echo and
also performs some noise reduction.

> Is there any document which answers these querries ?

Now there's the archive :-)


Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca>
Université de Sherbrooke
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