Muffinman wrote:
> I want to create a disfunctional volume control. I'm running MPD for
> playing music which uses hw:0 for playing back sound. However, I want to
> route the volume control to a sortof 'null' device and have a
> selfwritten application listen for changes in the volume level,
> translate and send that data to my amplifier through a serial port
> without it affecting the actual audio data stream to my USB-dac.
> pcm.blackhole {
> type null # Null PCM
> }
>
> However MPD now says its an invallid CTL blackhole
Because pcm.xxx is a PCM device, not a control device.
There is no 'null' control plugin, but for the softvol plugin,
ALSA has the ability to add 'user' controls to kernel drivers.
Ask "alsactl --help" where it stores its mixer settings file, and
add the following entry:
control.12345 {
iface MIXER
name 'Fake Playback Volume'
value 100
comment {
access 'read write user'
type INTEGER
count 1
range '0 - 100'
}
}
Then run "alsactl restore", check that it shows up in alsamixer,
and tell MPD to use that control.
Regards,
Clemens
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