Fedora, switch audio channels with pipewire
The lua configuration files are valid only for wireplumber v<0.5. Please check here for the configuration required on v=0.5. This post remains valid for what concerns retrieving the node name required in the config file.
I bought a pair Creative Pebble V3 and given my desk setup and the cables of the 2 speakers, I needed to switch left and right audio channels in order to setup correctly the speakers.
Now, I'm running Fedora Workstation and I never had to troubleshoot, manage, or change any audio settings besides adjusting volume when needed. I found out this task is not as easy as it seems, probably for a mixture of lack of documentation and lack of skills on my side.
At first I tried some promising GUI tools:
- EasyEffects -> with this one I was able to visually obtain what I wanted, ie switch channels, however I was not able to apply the changes anyhow.
- qpwgraph -> with this one I just got some background noise in my speakers and quickly gave up after successfully reverting the changes I made.
After this I found the wireplumber tool and that indeed worked. This Archlinux forum post pointed me in the right direction, however the post sample was doing something more than just switch channels and it wasn't working for me as it is.
First off, be sure that wireplumber is installed and enabled in your system:
wpctl status
You should get an output similar to this:
PipeWire 'pipewire-0' [1.0.1, davide@home, cookie:3084944151]
└─ Clients:
31. uresourced [1.0.1, davide@home, pid:2636]
32. WirePlumber [1.0.1, davide@home, pid:2666]
33. WirePlumber [export] [1.0.1, davide@home, pid:2666]
56. gnome-shell [1.0.1, davide@home, pid:2699]
57. pipewire [1.0.1, davide@home, pid:3375]
58. GNOME Shell Volume Control [1.0.1, davide@home, pid:2699]
59. GNOME Volume Control Media Keys [1.0.1, davide@home, pid:2914]
60. xdg-desktop-portal [1.0.1, davide@home, pid:3461]
61. Google Chrome input [1.0.1, davide@home, pid:5148]
62. Mutter [1.0.1, davide@home, pid:2699]
68. Boxes [1.0.1, davide@home, pid:6646]
69. wpctl [1.0.1, davide@home, pid:7334]
70. Boxes [1.0.1, davide@home, pid:6646]
Audio
├─ Devices:
│ 40. Pebble V3 [alsa]
│ 41. Navi 31 HDMI/DP Audio [alsa]
│ 42. Starship/Matisse HD Audio Controller [alsa]
│
├─ Sinks:
│ * 43. Pebble V3 Analog Stereo [vol: 1.00]
│ 44. Starship/Matisse HD Audio Controller Analog Stereo [vol: 1.00]
...
I tried this on a new VM running Fedora 39 Workstation image and it is working out of the box. The part that we are most interested in is the Sinks part. In my case it was the Pebble V3 Analog Stereo sink, the one I want to customize.
Let's use the ID to get more details:
wpctl inspect 43
Expect something like this:
id 43, type PipeWire:Interface:Node
alsa.card = "0"
alsa.card_name = "Pebble V3"
alsa.class = "generic"
alsa.device = "0"
alsa.driver_name = "snd_usb_audio"
alsa.id = "USB Audio"
alsa.long_card_name = "ACTIONS Pebble V3 at usb-0000:03:00.0-9, full speed"
alsa.name = "USB Audio"
alsa.resolution_bits = "16"
alsa.subclass = "generic-mix"
alsa.subdevice = "0"
alsa.subdevice_name = "subdevice #0"
api.alsa.card.longname = "ACTIONS Pebble V3 at usb-0000:03:00.0-9, full speed"
api.alsa.card.name = "Pebble V3"
api.alsa.path = "front:0"
api.alsa.pcm.card = "0"
api.alsa.pcm.stream = "playback"
audio.adapt.follower = ""
audio.channels = "2"
audio.position = "FR,FL"
card.profile.device = "1"
* client.id = "33"
clock.quantum-limit = "8192"
device.api = "alsa"
device.class = "sound"
* device.id = "40"
device.profile.description = "Analog Stereo"
device.profile.name = "analog-stereo"
device.routes = "1"
* factory.id = "18"
factory.mode = "merge"
factory.name = "api.alsa.pcm.sink"
library.name = "audioconvert/libspa-audioconvert"
* media.class = "Audio/Sink"
* node.description = "Pebble V3 Analog Stereo"
node.driver = "true"
* node.name = "alsa_output.usb-ACTIONS_Pebble_V3-00.analog-stereo"
* node.nick = "Pebble V3"
node.pause-on-idle = "false"
* object.path = "alsa:pcm:0:front:0:playback"
* object.serial = "43"
* priority.driver = "1009"
* priority.session = "1009"
There are two parts that we care about: node.name and audio.position. The first one is needed as an identifier, the ID is not stable so we can forget about it, while audio.position which has FR,FL value is the one we want to change to FL,FR to switch the channels.
rule = {
matches = {
{
{ "node.name", "equals", "alsa_output.usb-ACTIONS_Pebble_V3-00.analog-stereo" },
},
},
apply_properties = {
["audio.position"] = "FR,FL",
},
}
table.insert(alsa_monitor.rules, rule)
I saved this file as .config/wireplumber/main.lua.d/51-change-channels.lua (I got this filename checking samples and post online, not sure what the initial number is referring to and I suspect it's not that relevant unless you have multiple scripts in the folder) and run
systemctl --user restart wireplumber pipewire pipewire-pulse
That should be enough to have your audio channel switched. If it is not working, double check that the file has the correct format and run systemctl --user status pipewire* to check for errors.