Enable Surround Sound in Ubuntu Linux (PulseAudio) [How To]

By default, PulseAudio in Ubuntu up to Jaunty is set to work with 2 speakers (front channels).

Here is how to enable more than 2 speakers (channels) in Ubuntu - PulseAudio:

1. Edit the PulseAudio daemon.conf file by pressing Alt + F2 and enter:

gksu gedit /etc/pulse/daemon.conf

And search for: default-sample-channels. Remove ";" from the begining of the line, and instead of "= 2", change it to the number of speakers your system has. For instance if you have a 5.1 system, the number should be 6, for a 7.1 system: 8 and so on.
This is how that line used to look before you made any changes:

; default-sample-channels = 2

And this is how it's supposed to look after:

default-sample-channels = 6

2. Now you can save the changes and either restart your computer or:

killall pulseaudio && pulseaudio

3. Check to see if the channels are muted. Open a terminal and type

alsamixer

4. You can now test the channels by typing this in a terminal:

speaker-test -c 6

Again, replace the number with your number of speakers.