[Speex-dev] Echo Cancellation Problem -- with sound sample

Eddy
Sat, 22 Sep 2007 03:14:06 -0000

Hello all,

I am trying out the echo cancellation of Speex (1.2beta2) on Windows XP. I use
the Windows Media API (i.e. waveInOpen, waveOutOpen etc) for playback and
capture, but I cannot make echo cancellation works in my use case. Here is a
description of what I tried: (the sound is in 8kHz and 16 bits per sample, the
frame size is 240, tail_length is long enough to cover the far end to near end
delay)


Experiment 1:

A sine wave is generated in my test program (each frame has a random frequency).
And the echo cancellation function is called:

speex_echo_cancellation(echo_state, input_frame, echo_frame, output_frame);

where input_frame has a delay of 4560 samples compared to echo_frame (i.e. 570
ms delay). I output the output_frame to Windows Media API and playback in my
speaker. The echo cancellation performs quite well (around 10% noise/echo left).



Experiment 2:

A sine wave is generated in my test program (each frame has a random frequency).
But different from Experiment 1, I have the sine wave playback in my speaker and
then feedback to my microphone (by placing the microphone nearby the speaker).
echo_frame is the sine wave, and input_frame is the distorted sound after going
through my speaker and microphone.

This time, the echo cancellation is just like it does not exist. The output from
speex_echo_cancellation is "similar" to input_frame
("similar" in term of what I hear).

I have adjusted the delay between echo_frame and input_frame so that the delay
is small. Below is the output from echo_diagnostic.m:

octave-2.9.13.exe:61> echo_diagnostic('aec_rec2.sw',
'aec_play2.sw', 'aec_diagnostic.sw', 1024);
Far end to near end delay is 203 samples
Delay looks OK.
Drift estimate is 0.000000% (0 samples)
A drift of a few (+-10) samples is normal.



I do not have any clue to fix this problem now. I am sitting in front of my
computer for 2 days, trying out different things, but still cannot make obvious
improvement on echo cancellation. Is there anyone who have experience on this?
Is there anything I can try? Since I do not know how echo cancellation in Speex
works internally, I afraid there are some assumptions that I missed out.

I have a zip file ( http://idlechain.php0h.com/sound_sw.zip ) containing
ace_rec2.sw and aec_play2.sw in Experiment 2. Possibly it helps finding out the
problem.


Thanks,
Eddy






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