39

I'm currently running Ubuntu 9.04. I wanted to swap the stereo channels, but I couldn't find that option in the Volume Control Preferences.

Is there a way to do this without touching any configuration file? (I'm not allowed to log as root in this machine)

2
  • 1
    Swap the speakers?
    – user1686
    Oct 23, 2009 at 16:56
  • 4
    I have to have my speakers swapped. That's why I wanted to reswap the stereo channels :D
    – Auron
    Oct 26, 2009 at 16:18

4 Answers 4

44

The PulseAudio way (tested on Ubuntu 10.04, should work on 9.04):

Copy /etc/pulse/default.pa to ~/.pulse/default.pa, and add the following two lines to the end:

load-module module-remap-sink sink_name=reverse-stereo master=0 channels=2 master_channel_map=front-right,front-left channel_map=front-left,front-right
set-default-sink reverse-stereo

Restart PulseAudio by running pactl exit at the command line.

Leave out the second line if you don't want to use the reversed stereo by default. You can switch between reversed and normal stereo output in the "Output" tab in Sound Preferences. If you do have root and want this system wide, you can just add the lines to /etc/pulse/default.pa instead of making a user-specific configuration.

This configuration makes a few basic assumptions: that the card you're reversing the channels of is card 0; that you only have to deal with 2 channels; and that those channels are called front-left and front-right.

If you have a videocard with HDMI out, it is likely the analog out of your motherboard will be card 1, not 0; so master=1. (Front Panel headphones are likely on this analog channel)

For more information, see the PulseAudio documentation for module-remap-sink.

7
  • Initially it seemed to do the trick on 14.04. But after reboot pulseaudio daemon failed to start. had to remove the call to fix it.
    – Amir Uval
    Jun 26, 2014 at 13:54
  • Works via pacmd too (i.e. no need to copy config & restart pulseaudio).
    – ulidtko
    Oct 6, 2014 at 9:52
  • 1
    If you have more sinks, so you can use pacmd list-sinks to display a list of existing sinks and their indexes. than replace master=0 with the master=IndexOfTheSinkToSwap Jul 15, 2016 at 8:36
  • 2
    This works perfectly under Ubuntu 16.04 as well. Persists through reboot as expected.
    – Elder Geek
    Jul 31, 2016 at 16:06
  • Great answer! Only problem I'm having is that the volume of the remapped sink is based on the base sink. That means if I switch to the base sink and turn volume to 50% the remapped sink will now be able to go up to only 50% volume (it's 100% will be the 'real' 50%). Any way around that?
    – srfrnk
    Apr 28, 2019 at 6:00
20

Essentially the same approach as Brian's above, but without touching any configuration file:

pactl load-module module-remap-sink \
    sink_name=reverse-stereo \
    master=0 \
    channels=2 \
    master_channel_map=front-right,front-left \
    channel_map=front-left,front-right

This will create on the fly an additional PA sink with reversed channels. (It will disappear after pulseaudio restart). To switch to it:

pactl set-default-sink reverse-stereo

— OR, you can also switch manually via the sound control panel:

pulseaudio volume control window

Off course it's possible to switch back and forth, e.g. when experimenting.


This way is better if you want to try something out quickly rather than to save the setup permanently.

5
  • pactl set-default-sink reverse-stereo failed with No valid command specified. on a Ubuntu 12.04.
    – Auron
    Oct 6, 2014 at 11:41
  • 1
    @Auron works fine on 14.04.
    – ulidtko
    Oct 8, 2014 at 0:43
  • Hmm, I would have to check it.
    – Auron
    Oct 16, 2014 at 12:10
  • 1
    @Auron, see update; you can also switch manually via the sound panel.
    – ulidtko
    Oct 16, 2014 at 13:41
  • 2
    Amazingly, this solution still works as of Ubuntu 19.10. Just that after pactl set-default-sink reverse-stereo you have to restart sound-playing applications (like Firefox) so that they pick up the new default on restart.
    – tanius
    Feb 10, 2020 at 15:17
7

If you're using ALSA, Add this to your ~/.asoundrc file:

pcm.swapped {
    type         route
    slave.pcm    "cards.pcm.default"
    ttable.0.1   1
    ttable.1.0   1
}

pcm.default      pcm.swapped

Via ALSA FAQ

4
  • +1 beat me by seconds... note Ubuntu 9.04 installs PulseAudio by default which probably has its own way to do it. Oct 23, 2009 at 15:34
  • @ ~quack doesn't PulseAudio route the sounds to ALSA ?
    – Sathyajith Bhat
    Oct 23, 2009 at 15:43
  • yes, just sayin' PA can probably do the swap on its own, on the There's More Than One Way To Do It principle. :) Oct 23, 2009 at 15:44
  • @~quack Ah, Gotcha ;)
    – Sathyajith Bhat
    Oct 23, 2009 at 15:47
0

I have the same problem here and the Brian answer works fine on some devices. If you want to invert the stereos of bluetooth devices every time you restart PulseAudio the sound device conected by bluetooth will disconect and after reconecting there is no remaped audio output. Probably a way to reload conected devies without restarting PulseAudio solve this issue.

2

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