[Speex-dev] Help needed regarding Echo Cancellation

[Shantanu Gramsci]

Dear all, 

I need to use echo cancellation in a VOIP application
using speex narrowband codec.I am facing some problems
with echo cancellation. It will be very helpfull if
someone can put some light on the following issues.

1: 
===================

-- When call is started EC works fine for first few
seconds. Bur after a certain period [usually 20 sec or
more] it does not work or works very bad [produces
distorted or noisy echo].

-- If no one talks for some time [around 4/6 mins] EC
works again for some period and after that period it
fails again. 

-- I used echo tail 200ms. Using long echo tail
[2000ms], EC works very fine but in that case CPU
usage becomes very high. 

What should be the solution in this situation? I mean
what can be the reason that EC fails after some time.


2: 
====================

-- I read the played packets from DirectSound Buffer
and use it as echo frame. I have noticed that my echo
frame is of low amplitude and many values of it are 0
[zero]. 

-- Since the values are small, I applied AGC on echo
frame with another Speex preprocessor before passing
it to EC. With this approach and echo tail 400ms, I
get very good echo cancellation. But some times we get
distorted audio, sounds like someone speaking in pipe
or underwater.
-- Is there any possibility to get distorted audio if
we apply speex AGC on echo frame before passing it to
EC? 

3:
==============
-- Is there any tradeoff that if echo cancellation
becomes more aggressive, the voice quality will fall
or will be distorted?
-- What are the ways to make EC more aggressive?
 

Any help is greatly appreciated. Thanks in advance.
 

Shantanu

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