[Speex-dev] feedback about speex 1.1.6 [echocancel]

Ard van Breemen ard at kwaak.net
Wed Aug 25 02:59:28 PDT 2004

On Sat, Aug 07, 2004 at 05:14:49PM +0800, xuehz wrote:
> hello! speex-dev friends??
>   		I am doing some work about echo cancel test! I
>   		test echo cancel function of speex(1.1.6),find
>   		some question!

>         1.  when echo cancel  is effect , the time has elapsed
>         about 20 second , it is too long for using,must
>         shorten!

The filter is adaptive, it needs to learn... If you do not throw
away your echostate, then next time it just might pick up where
it left of. Most loudspeaker telephones (the expensive ones) have
a special learn function to adjust to surroundings. They will
start beeping to train the filter...

>         2.  when PC CPU is busy, sometimes the effect of echo
>         eancel will be bad and will continue!

Are you sure you did not loose a frame, which means that the
filter adaption is bogus (just guessing if that is the case).
Another case with the filter is that it has problems adapting
when there are single frequency signals on the line, like a
dialing tone. This wil get you a beeping echo for the next 20

>         3.  how can I decide the effect of echo cancel in program ?
>             I think when the effect is bad , we can restart echo cancel !
>             Is it right?

But then you have to train the filter again... :-)

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