[Speex-dev] How to use aec correctly?

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Tue Aug 8 18:42:24 PDT 2006

On Tue, 2006-08-08 at 17:38 +0800, keith wrote:
> Hi,all
>   I have tested AEC on files, it works well.I have some files,one is echo
> file, others are echo-added files(an origin file adding echo at different
> delay,such as 20ms,40ms...120ms,140ms).AEC do wonderfully on those files
> except echo added at 140ms-delay.

The longer the delay, the smaller the "effective" part of the filter

>   But ,when i use AEC in my voip project, it does feebly. Who can give me
> some hints why caused this.How long can  sound be picked up by mic after it
> plays out.This is the main problem to align echo.Give me a hint.

What I recommend: 
1) Read the *new* version of the manual (the one on the website hasn't
been updated in a while)
2) record your input and output to a file so you can look at them and
perform AEC offline (i.e. you can actually see what happens)
3) Have a look at Echo Cancellation Demystified


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