[alsa-devel] Output to Input routing

Takashi Iwai tiwai at suse.de
Thu Aug 2 14:30:57 CEST 2007

At Tue, 31 Jul 2007 14:33:04 +0000 (UTC),
Vadim Lebedev wrote:
> Hello,
> I remember reading AC97 specs that there si possibility to configure it
> in such a way, that when doing stereo capture, left input channel will get
> actual MIC input and  right input channel will get the copy of speaker output.
> This setting is ideal for echo cancellation algorithm.
> To my grand dismay i'm unable to find a doc of ALSA mixer API so i'm
> unsucessuful  writing code to put mixer in such mode.  
> Can some kind soul please contibuite a code snippet....

Choose "Mix" as the capture source will give you the loopback input
for the specific channel.  You can change it via amixer, for example,

	% amixer cset iface=MIXER,name='Capture Source' 0,5
	numid=66,iface=MIXER,name='Capture Source'
	  ; type=ENUMERATED,access=rw------,values=2,items=8
	  ; Item #0 'Mic'
	  ; Item #1 'CD'
	  ; Item #2 'Video'
	  ; Item #3 'Aux'
	  ; Item #4 'Line'
	  ; Item #5 'Mix'
	  ; Item #6 'Mix Mono'
	  ; Item #7 'Phone'
	  : values=0,5


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