[Speex-dev] Echo cancellation questions

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Mon Aug 29 16:02:45 PDT 2005

> 1. In the manual it's stated that the delay between the input signal
> and the echo signal must be small. How small should it be? Is for
> example 100 ms acceptable?

100ms would probably work, but less is always better. If you know it's
100ms, all you have to do is delay the far end signal.

> 2. Does echo cancellation algorithm deal well with situation, when one
> of the users of Speex-based VOIP application has
> "record-what-you-here" sound card mixer option selected? Did anybody
> test the algorithm in such conditions? In an application I'm working
> on the result is not nice - both users (especcialy the one with
> mentioned option enabled) hear periodic (approx. once a second) loud
> noise ("knocks"), which seems to be an effect of amplification of
> background noise caused by echo. Am I using speex_echo_cancel
> improperly or it's not possible to eliminate echo in such conditions?

The problem is that the feedback loop (with gain > 1) builds up before
the echo canceller has time to adapt. 

> 3. Does e.c. algorithm works as good in wideband as in narrowband
> mode?

Should work, haven't tested it.


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