Speakers go to 100% volume instead of being muted when plugging in headphones

Question

My speakers are connected over SPDIF and when I plug in headphones (front of case), the speaker volume goes to 100% and back to its normal volume when I remove the headphones.

While the headphones are plugged in, the volume media keys change for the headphones but the speakers remain at 100%. So the system does switch to headphones but does not mute the speakers.

I have spend several hours looking for a fix in pulseaudio, alsa and udev but only found either outdated or not applicable solutions.

1. Is this a pulseaudio, alsa, kernel module or udev problem?
2. Where can I see what exactly is happening? There don't seem to be default log files.
3. How do I fix this?

Answer 1

While looking for information to extend my question I surprisingly stumbled upon a solution/workaround, although I don't understand what exactly is going on. Maybe this is useful to someone. Maybe someone can provide an explanation on what is going on.

Observation

In alsamixer I have four SPDIF channels and all of them were unmuted (OO)

I found that while no headphones are plugged in, S/PDIF and S/PDIF 16 (outer channels) must be turned on for sound to be outputted. The other two (2nd and 3rd) have no effect.

When I plugged in headphones only S/PDIF 16 had any effect on sound of the speakers.

Solution

Although the inner SPDIF channels have no effect on sound no matter whether headphones are plugged in or not, they do seem to change something that makes the sound switch work.

While the headphones are not plugged in, mute the inner channels S/PDIF Default and S/PDIF 1 by using cursor keys ← and → to select the appropriate channel and then m to mute, like so:

Now when you plug-in headphones the speakers are muted.

To make this persistent between reboots, run as root

# alsactl store