[alsa-devel] Individual PCM stream control

Takashi Iwai tiwai at suse.de
Thu Mar 29 13:52:17 CEST 2007

At Thu, 29 Mar 2007 05:56:50 -0500,
Nagalla, Hari wrote:
> Hello,
> I am new to ALSA, so some help from experienced folks would help.. 
> We are trying to develop ALSA support for our DSP based mixer. In our
> architecture DSP performs the mixing, sample rate conversion etc. My
> question is how, can does the user space applications exercise
> controlling individual PCM stream to the mixer? Ex: individual stream
> gain control, individual stream mute, etc.. Any user space example code
> would be useful too..

Most drivers create PCM volume controls with IFACE_PCM tag, and set up
the volume appropriately at each PCM open, or let alsa-lib configs to
set up the initial volumes.  Usually, the control element index
corresponds to the PCM substream number.

The controls with IFACE_PCM are not visible from normal mixer apps.
(The mixer sees only IFACE_MIXER elements.)  So, if you need a dynamic
control of such elements, you'll likely need a special program to
access the corresponding elements.


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