ALSA mono output

Mr. Alex · 06-19-2010, 07:43 AM

Mint 9, Gnome. No PulseAudio, just ALSA. How do I switch audio output from stereo to mono and from mono to stereo again? Please don't tell me to install PulseAudio, I don't want to.

keithieopia · 06-20-2010, 12:50 AM

I don't blame you for not wanting PulseAudio!

Anyway create/edit ~/.asoundrc and place the following in it:

Quote:

pcm.card0 {
type hw
card 0
}
pcm.mono {
type route
slave.pcm card0
slave.channels 2
ttable.0.0 0.5
ttable.0.1 0.5
ttable.1.0 0.5
ttable.1.1 0.5
}

This creates a virtual soundcard (or the correct term is: "slave") named "mono". You can then play anything you want in mono by selecting it. For instance the following two commands will create very different output (the Noise.wav is probably in a different location on your machine):

Quote:

aplay -D mono /usr/share/sounds/alsa/Noise.wav
aplay -D default /usr/share/sounds/alsa/Noise.wav

If you want the default to be in mono, add the following in addition to what you added to .asoundrc before.

Quote:

pcm.!default {
type route
slave.pcm card0
slave.channels 2
ttable.0.0 0.5
ttable.0.1 0.5
ttable.1.0 0.5
ttable.1.1 0.5
}

NOTE: You'll probably have to restart ALSA or logout and back in again.

Mr. Alex · 07-21-2010, 04:08 AM

Where should I choose the sound card? "gstreamer-properties"? But there's no "mono" soundcard...