Ubuntu – Adjust PCM volume

There are many layers in the audio stack that could contribute to this symptom. Most directly is the behavior that PulseAudio defaults to, and you can read about that at http://pulseaudio.org/wiki/PulseAudioStoleMyVolumes. You can work around some instances using the instructions I contributed at https://wiki.ubuntu.com/DebuggingSoundProblems/KarmicCaveats#Volume%20range%20anomalies:

Volume range anomalies

The latest version of PulseAudio tries to control the volume of the sound card using its mixer controls. Usually this works just fine, but in some cases this does not work properly. (Whether this is PulseAudio's or ALSA's fault is beyond the scope of this wiki page. Some more background information is here.)

Diagnosis

You experience any of the following:

• Jumps in volume, e g if everything below 20% is muted, and 21% is very loud.
• Overdriven (distorted sound) if the volume is set above a certain (low) level
• No volume changes in parts of the range, e g if 20% is just as loud as 70%.

Fix / Workaround

There are a few variables which control how PulseAudio controls the volume. You can either edit /etc/pulse/default.pa (you'll have to be root to do that) to change the behavior for all users, or copy that file to ~/.pulse/default.pa and then edit that file, to change behavior for the current user only.

Open the file mentioned above. Find the row saying load-module module-udev-detect and change it to:

load-module module-udev-detect ignore_dB=1

To try your changes, restart PulseAudio with the following command:

killall pulseaudio

PulseAudio will then autospawn (restart itself).

You may find that the above workaround is insufficient, in which case you may configure PulseAudio to control only one mixer control, e.g., PCM (cf. alsamixer). Find the row saying #load-module module-alsa-sink and change it to:

load-module module-alsa-sink control=PCM

(remember to remove the # in the beginning of the row!) Optionally replace PCM with the mixer control you want PulseAudio to control.

You will then need to killall pulseaudio as above and allow the daemon to autospawn.

Finally, whether this anomaly is actually a bug requires you to use ubuntu-bug alsa-base.

With PulseAudio 8.0 on Ubuntu 16.04 and a single sound card, you can set the default master volume to 50% with the following file. By including the system default you don't have to worry about changes in the distribution's defaults.

$ cat ~/.config/pulse/default.pa
.include /etc/pulse/default.pa

# Set volume to 50% on boot
set-sink-volume 0 32768

If you have multiple cards, replace the index number with the name since order is not guaranteed. In addition, if you want to adjust the volume determine the "base volume" which represents the max and calculate the equivalent percentage.

$ pacmd list-sinks | grep -e "name:" -e "index:" -e "base volume:"
  * index: 0
    name: <alsa_output.card0>
    base volume: 65536 / 100% / 0.00 dB
  * index: 1
    name: <alsa_output.card1>
    base volume: 32768 / 100% / 0.00 dB

For example, to specify the default volume of 70% for card1 the line would become:

set-sink-volume alsa_output.card1 22937