[speex-dev] Re: Speex 1.1 is out

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Fri Sep 19 20:11:58 PDT 2003

> 1) What should I use for a filter length for speex_echo_state_init()? 

Well, it depends on your problem. The filter length represents the
maximum delay of the echo. For acoustic echo, that value is generally
higher than for line echo. You'll need to experiment, but a value around
500 (for 8 kHz) might be a good start.

> 2) I'm assuming I want to call speex_echo_cancel() on each incoming 
> frame to be played back. But, what do I pass for the parameters? 
> I'm guessing that ref is the current outgoing frame, echo is the 
> current incoming frame (which contains echo to be removed), out 
> is the echo-cancelled frame to be played back, and Yout is the 
> same signal as out but in the frequency domain. Is this right? 

Actually, ref is the incoming frame (with echo), echo is the outgoing
frame (that has only the echo) and out is the echo-cancelled frame. As
for Yout, it is an estimation of the residual echo that can be sent to
the denoiser so that residual echo can be removed as well. Note that
this last feature is still experimental.

> 1) I'm assuming the timestamp should be in milliseconds. (Does it 
> matter?) 

Yes, it should be in milliseconds and yes, it does matter.

> 2) Do you anticipate any problems using VBR with the jitter buffer? 

There shouldn't be any special problem with VBR. If there is, it's just
a bug. The jitter buffer hasn't been tested that much yet.


Jean-Marc Valin, M.Sc.A., ing. jr.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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