unwanted echo of audio input

unwanted echo of audio input

[Chris Raphael]

Alsa Folks,
  I am using ALSA 9.0 on a Dell Inspiron 8200 which uses the Intel 
82801CA-ICH3 card and CS4205 chip set.  I am writing a program
that simulaneaously samples and plays audio.  The problem I am
having is that everything that is captured by the microphone is
automatically echoed to the speaker.  I have tried all of the
mixer settings I can think of using alsamixer and cannot make the
problem go away.  I have also tried to fix the problem from a c
program using the OSS-style commands

  fd = open("dev/mixer",O_RDWR);
  vol = 0;	
  ioctl(fd,MIXER_WRITE(SOUND_MIXER_IMIX),&vol);
 
but without success --- the volume value is set to 0, as it should be,
but no change in what actually happens.  (All of my other sound-related
code uses the ALSA API).  
  

I am thinking that it is possible to avoid this echoing since, using
Windows, I was able to play from the cd and record without a similar
mixing of input and output on the same machine.

I would really appreciate any help with this.  It might not be relevant,
but the program I'm working on is an automatic accompaniment system.
The input is the soloist's musical sound signal and the output is
the orchestra recording, warped to follow the soloist.
There are some nice examples on my the web page: 

 http://fafner.math.umass.edu/music_plus_one

Christopher Raphael


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Re: unwanted echo of audio input

[Takashi Iwai]

At Sun, 15 Jun 2003 13:08:13 -0400,
Chris Raphael wrote:
> 
> 
> Alsa Folks,
>   I am using ALSA 9.0 on a Dell Inspiron 8200 which uses the Intel 
> 82801CA-ICH3 card and CS4205 chip set.  I am writing a program
> that simulaneaously samples and plays audio.  The problem I am
> having is that everything that is captured by the microphone is
> automatically echoed to the speaker.  I have tried all of the
> mixer settings I can think of using alsamixer and cannot make the
> problem go away.  I have also tried to fix the problem from a c
> program using the OSS-style commands
> 
>   fd = open("dev/mixer",O_RDWR);
>   vol = 0;	
>   ioctl(fd,MIXER_WRITE(SOUND_MIXER_IMIX),&vol);
>  
> but without success --- the volume value is set to 0, as it should be,
> but no change in what actually happens.  (All of my other sound-related
> code uses the ALSA API).  

this echo volume corresponds to "Mic Playback Volume" and "Mic
Playback Switch".  these values have nothing to do with the capture
volume.  please try to mute "Mic" volume in alsamixer.


Takashi


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