[alsa-devel] Individual PCM stream control

Nagalla, Hari hnagalla at ti.com
Fri Mar 30 12:47:11 CEST 2007

Thanks for the advice.. Couple of inline questions below..

> -----Original Message-----
> > 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
> > 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
> > gain control, individual stream mute, etc.. Any user space example
> > 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.

Which alsa library API lets us to set up the PCM stream volume? And can
it be used dynamically when the stream is active?
I could n't figure out 'index' of the control element. Can you please
explain which parameter of the 'struct snd_ctl_elem_value' you are
referring to..
> 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.
> Takashi

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