HOWTO: 4 Channel output with RhythmBox

[EvanL]

Note: Scroll down to post #3 for a much better way to do this.

Finally figured out how to get 4-channel output from RhythmBox for MP3 Playback. This HOWTO is for ICH8x0 AC'97 cards, although it may work for other sound systems. Basically, YMMV.

1) Create a .asoundrc file in your home directory.

gedit ~/.asoundrc

2) Copy the configuration from this thread (http://www.ubuntuforums.org/showthread.php?t=167986&highlight=.asoundrc+xmms) into the new file.

pcm.ch40dup {
type route
slave.pcm surround40
slave.channels 4
ttable.0.0 1
ttable.1.1 1
ttable.0.2 1
ttable.1.3 1
}

pcm.ch51dup {
type route
slave.pcm surround51
slave.channels 6
ttable.0.0 1
ttable.1.1 1
ttable.0.2 1
ttable.1.3 1
ttable.0.4 0.5
ttable.1.4 0.5
ttable.0.5 0.5
ttable.1.5 0.5
}


3) Run gstreamer-properties

gstreamer-properties

4) Under "Default Output Plugin," choose "Custom" then enter the following line in your Pipeline input box.

alsasink device=ch40dup

5) That's it! Test RhythmBox to make sure it works!

Note that entering alsasink device=ch51dup should work for 5.1 systems, but I don't have a 5.1 system to test it on, so that one's up to you.

An interesting note is that the alsamixer slider volume control for surround doesn't work, but the surround mute function does work.

[EvanL]

Update, I found a better way to do this:

Use the code found here (http://alsa.opensrc.org/FAQ028) for your .asoundrc file. Note that I changed "hw0,1" to "hw0,0". Code is pasted below:

pcm.dmixs51 {
type dmix
ipc_key 1024
slave {
pcm "hw:0,0"
rate 48000
channels 6
period_time 0
period_size 1024
buffer_time 0
buffer_size 4096
}
}
pcm.duplicate {
type plug
slave.pcm "dmixs51"
slave.channels 6
route_policy duplicate
}


Now in gstreamer-properties, change your output plugin to:
alsasink device=duplicate

Now you should have downmixing capabilities in addition to playing stereo files on multiple channels.

-Evan

[EvanL]

New .asoundrc file. This works for me on the Intel ICH8x05 chipset. Aoss and ALSA will play together nicely, but for the life of me, I can't get firefox to output sound when I'm running another sound source. Unbelievably annoying. Anyway, here's the file:

# Set default sound card
# Useful so that all settings can be changed to a different card here.
pcm.snd_card {
type hw
card 0
device 0
}

pcm.dmixs40 {
type dmix
ipc_key 1024
ipc_key_add_uid false
ipc_perm 0666
slave {
pcm "snd_card"
rate 48000
channels 4
period_time 0
period_size 1024
buffer_time 0
buffer_size 4096
}
}

pcm.duplicate {
type plug
slave.pcm "dmixs40"
slave.channels 4
route_policy duplicate
}

pcm.input {
type dsnoop
ipc_key 2048
ipc_key_add_uid false
ipc_perm 0666
slave.pcm "snd_card"
}

pcm.asym40 {
type asym
playback.pcm "dmixs40"
capture.pcm "input"
}

pcm.!defualt{
type plug
slave.channels 4
slave.pcm "asym40"
bindings{
0 0
1 1
2 2
3 3
}
}

###############
# OSS #
# Emulation #
###############

pcm.dmix0 {
type dmix
slave {
pcm "hw:0,0"
rate 44100
channels 2
}
}

pcm.dsp0 {
type plug
# slave.channels 4
slave.pcm "dmix0"
# slave.pcm "dmixs40"
# ttable.0.0 0.5
# ttable.1.1 0.5
# ttable.0.1 0.5
# ttable.1.0 0.5
}