How do you set a default audio output device in Ubuntu?

Simple fix in 19.10 that worked for me:

I couldn't get the solution @singrium proposed to persist on Ubuntu 19.10. It worked with device numbers in /etc/pulse/default.pa but as I connected for example my headset device numbers were changing and things stopped working. It didn't work with device names in /etc/pulse/default.pa.

The simple workaround I found is adding the pactl set default sink command in startup applications.

1. Run: pactl list short sinks
2. Note the device name you want to use as default
3. Try to run: pactl set-default-sink <Your_Device_Name>
   This should work without giving you an error message.
4. Open the application "Startup Applications" (Should be preinstalled on Ubuntu)
5. Click on "Add"
6. Give your startup item a name
7. Copy your command from above into the command field:
   pactl set-default-sink 'Your-Device-Name'
8. Click on "Add".

You are now good to go. Your default audio device will be set on each boot and as such be persistent. If you want to change the default device simply edit the device name in startup applications command.

EDIT (05/03/2020):
It seems that @phanky5 figured out a simpler solution. Please check it before you try this one.

Here is a well explained tutorial to set a default audio input/output.

First: List the audio output devices using

pactl list short sinks

Example output:

43  alsa_output.pci-0000_00_1b.0.analog-stereo  PipeWire    s32le 2ch 48000Hz   IDLE
1076    alsa_output.usb-Logitech_Logitech_Wireless_Headset_4473D63ED97A-00.analog-stereo    PipeWire    s16le 2ch 48000Hz   IDLE

Second: To set a default output device, run the command

pactl set-default-sink <'output_device_name'>

Example: pactl set-default-sink 'alsa_output.pci-0000_00_1f.3.analog-stereo'

If you switch sinks a lot, you can use fzf to select one via the command line and make it the default:

pactl set-default-sink $(pactl list short sinks | cut -f2 | fzf)

To make the sink permanently the default, follow this:

First, open the file /etc/pulse/default.pa using:

sudo -H gedit /etc/pulse/default.pa

Then scroll to the bottom of the file, where two lines starting with set- will be commented out.

Now, uncomment these lines and replace the words input and output with the number of the sink (for output) / source (for input) that you want to be the default.

Example (sets both default input and output):

### Make some devices default
set-default-sink 3
set-default-source 3

PS: As discussed in the comments with Bim, it is also possible (according to him) to put the input/output name in /etc/pulse/default.pa instead of the input/output number.

Example:

### Make some devices default
set-default-sink alsa_output.pci-0000_00_1f.3.analog-stereo
set-default-source alsa_output.pci-0000_00_1f.3.analog-stereo.monitor

After doing this, save and exit. Then, delete the ~/.config/pulse directory by running rm -r ~/.config/pulse, and then reboot the system. Once the system reboots, the appropriate devices should now be set as the defaults.

EDIT:
As mentioned by ahmorris in his answer, some had to comment this line load-module module-switch-on-connect in the file /etc/pulse/default.pa to be # load-module module-switch-on-connect in order to make the changes persistent.

To make Singrium's answer work, I had to comment out this line from my /etc/pulse/default.pa by adding the #:

# load-module module-switch-on-connect

Otherwise, on startup my audio device would be set to my default device, but then would switch to my USB hub once it was detected. This prevents that switch and ensures your chosen audio device is the output.

This can be done with PulseAudio Volume Control if you prefer to use a GUI.

Once you've opened PulseAudio Volume Control, choose the configuration (the last tab), then select the output and/or input you want to use from the profile dropdown menu. It should look similar to this

PulseAudio Volume Control can also be used to adjust volume levels for each input, output, system sounds and applications that are currently in use.

Here's a post from Linuxhint with more info on PulseAudio.

This worked for me in Ubuntu 20.04.

Like was said before you have to list the audio output devices:

pactl list short sinks

And than you can add your chosen device to /etc/pulse/client.conf file like this:

default-sink = alsa_output.pci-0000_00_1f.3.analog-stereo

NOTE: You have to remove the "!" from the original line. In Ubuntu 20.10, you have to remove the ";" from the original line.

In my case, on my Bionic/18.04.3 changes in /etc/pulse/default.pa doesn't works (1)!

pactl list short sink
…
2   alsa_output.pci-0000_00_1f.3.analog-stereo …

pactl set-default-sink 2 
# or 
pactl set-default-sink 'alsa_output.pci-0000_00_1f.3.analog-stereo'

works fine in CLI,

make change in my ~/.profile based on post How to startup a script automatically after login, add line:

pactl set-default-sink 'alsa_output.pci-0000_00_1f.3.analog-stereo'

and it works after reboot

(1) I have some error en my /var/log/syslog in all case with number or all text:
[pulseaudio] main.c: Sink output 2 does not exist.
[pulseaudio] main.c: Sink output 'alsa_output.pci-0000_00_1f.3.analog-stereo' does not exist.

Ubuntu already stores the last selected audio device across reboots. Just things like USB docking stations or HDMI devices might mess up this mechanism, because they are detected as last device during boot and Ubuntu thinks, they just got connected.

So the most simple solution would be in many cases, only to comment the automatic switching on connect (load-module module-switch-on-connect) as outlined in this answer: https://askubuntu.com/a/1115641/39966

All the set-default-sink / -source commands or configurations may be not needed in most of the cases.

At the end of the day this was / is a bug in Ubuntu, which is at least for HDMI devices considered to be solved in recent versions. There is still another open bug for USB devices.

See also Selected Sound Output Device Not Persisting Between Reboots in gnome-control-center

You can achieve this just using pulseaudio standard configuration file to do the following:

• disable automatic switching to new plugged devices
• set the default device

Steps

List your devices:

pactl list short sinks

Copy the name of the device that you want to make the default. Names are long. Something like alsa_output.pci-0000_00_1f.3.analog-stereo.

Now let's configure pulseaudio:

sudo nano /etc/pulse/default.pa

Disable the pulseaudio switching to the latest plugged device. For this, make sure the following lines are starting with a #:

#ifexists module-switch-on-connect.so
#load-module module-switch-on-connect
#.endif

Now go to the bottom of the file and make your device the default:

set-default-sink '<your-device-name-here>'

Save the file and exit.

Restart pulseaudio with pulseaudio -k.

Sometimes you need to delete the entire ~/.config/pulse folder.

This worked for me.

You can ignore the bit about having to change via command line, the bit that fixed the audio devices resetting was editing the /etc/pulse/default.pa file. Change line load-module module-stream-restore to load-module module-stream-restore restore_device=false and then restart pulse audio with pulseaudio -k.

You should now be able to update the audio sink and source via settings > sound and they should persist past a log out/in and system restart.

I had my rear panel and webcam mics. The issue was that every time I turned my PC on, the webcam mic was the default, instead of the desired rear panel mic. So I went ahead and installed pavucontrol and at the Configuration tab I simply turned it off, for god's sake:

sudo apt install pavucontrol

Then run:

pavucontrol