[Speex-dev] Sound card problem in acoustic echo

LiMaoquan2000 LiMaoquan2000 at 126.com
Thu Sep 30 01:45:14 PDT 2010

Hi All,
In order to deal with acoustic echo cancellation problems of most PCs which
sound cards have different capture and play frequencies. I made a trial.
At first, a 1000Hz sine wave is played for a long time via a speaker and its
acoustic echo is recoreded.
Seconds, get the frequency of the echo by a FFT analyser. So the difference
between capture and play frequencies is obtained.
Thirdly, before AEC, the signal captured by the soundcard is resampled to the
play frequency. The frequency step of the resampler is 0.1Hz. So for the AEC,
the difference between far-end signal and near-end signal is no more than 0.1Hz.
I have tested the speex AEC and my own AEC in a PC that the difference between
its sound card is about 0.8Hz. They show the same result :
WITHOUT the resampler, just a little acoustic echo is eliminated.
WITH the resampler, most acoustic echo is eliminated. But it still can be heared
clearly, even though the echo is faint.
This performance is still much worse than AEC in PCs which sound cards have same
capture and play frequencies. There is almost no echo can be heard in latter.
Does anybody have advices to this problem? It's a common problem for acoustic
echo cancellation in most computers, because most sound cards have different
 capture and play frequencies. It vital for all acoustic echo cancellers.
Any advice is welcome.
>Date: Sun, 25 Jul 2010 20:26:44 +0000 (GMT)
>From: p_j_r_m <p_j_r_m at yahoo.com>
>Subject: Re: [Speex-dev] Sound card problem in acoustic echo
>To: speex-dev at xiph.org
>Direct Sound AEC never worked for me, even when it did with Speex.?I was told that after disabling effects in DS the play and record streams could be synchronized,and then Speex AEC did the job.
>--- El vie, 23/7/10, limaoquan2000 <limaoquan2000 at 126.com> escribi?:
>De: limaoquan2000 <limaoquan2000 at 126.com>
>Asunto: Re: [Speex-dev] Sound card problem in acoustic echo
>Para: speex-dev at xiph.org, p_j_r_m at yahoo.com
>Fecha: viernes, 23 de julio, 2010 22:42
>>I remember?I had to expose the echo cancelation level implementing a get_echo_level( ) function based on this:
>This is really a good idea to determine the frequency difference between capture
>and play of the sound card. But it need constant far-end voice and a long time
>because it must repeat the process of "resampling, test echo" for many times.
>Have you tried the AEC in DirectSound? If this AEC is usable for all sound cards,
>perhaps microsoft has solved this problem already. Can we choose proper options
>of the DirectSound to solved this problem and disable its AEC at the same time?
>>Using that value and averaging samples as?"fedback" I did small corrections to sampling rate until convergence, although this not always worked.When it did, convergence was quite fast (seconds).
>>Resampling did not introduce noticiable CPU increase.But may be the small time used for conversions was the cause of non-convergence.I think this path is hard and uncertain,
>>and now,i would dive first in DirectSound to try to obtain synchronized streams before passing them to speex.
>Waiting for your good news.
>>Regarding ASIO, you have to install a special "driver"? for it to work,and this seems unaceptable for general users.
>>--- El jue, 22/7/10, limaoquan2000 <limaoquan2000 at 126.com> escribi:
>>Thank you.
>>But it will cost you a long time to get the accurate play and capture frequencies.
>>Does your program test two frequencies of the sound card each time Because
>>different sound cards have different frequency errors.
>>And the resampling program is also time consuming because the target frequency is
>>so close to the sampling frequency of the input signal, isn't it?
>>I have tested program based on Windows waveform functions and also DirectSound.
>>They have similar frequency error.
>>BTW: What's your conclusion of ASIO driver? Why "it was of no practical use"?
>>> I worked some time for a company doing AEC using Speex on Windows.It is true it depends a lot on sound card models. I remember I could do AEC by resampling frequencies so play and record frequencies where equal.Frequencies where aprox 100Hz appart.Also, I know that on other cases AEC was achieved by disabling FX DirectSound effects where it wasn`t possible before that.Try to disable all you don't need before calling Speex AEC function.
>>> Also, I tried the ASIO driver,as an experiment. I think it worked, but it was of no practical use.
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