Bug 464192

Summary:	Opening the PulseAudio applet automatically changes bluetooth headset to headset mode
Product:	[Plasma] plasmashell	Reporter:	zsolt
Component:	Audio in general	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	CONFIRMED ---
Severity:	normal	CC:	isma.af, nate, nicolas.fella, nowrep
Priority:	NOR
Version First Reported In:	6.2.4
Target Milestone:	1.0
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description zsolt 2023-01-12 14:20:01 UTC

SUMMARY
***
When clicking on the PulseAudio applet in the task bar while listening to music on my bluetooth headsets, the applet starts listening to the headset's microphone and thus changes it to "headset" mode (mSBC), which is terrible for music (it has a much louder profile, bad audio quality, and is in mono). This makes it very impractical to use the applet to change volume, or do any other changes while listening to music. I suspect the applet listens to music to show a volume bar (which is a nice idea but has this unfortunate side-effect). After the applet stops listening to the microphone, my headset would automatically switch back to high-quality headphones mode (A2DP).

I own a Plantronics BT600 headset which I use with its USB dongle, and thus I am not connecting it directly to my computer through bluetooth, so no PulseAudio/PipeWire/WirePlumber is involved in this switching. I believe this is pretty common practice amongst similar headsets.

STEPS TO REPRODUCE
1. Connect some bluetooth headset that behaves as explained above
2. Start listening to music
3. Click on the PulseAudio applet with the intention of changing the volume

OBSERVED RESULT

Now your ears are blasted with loud, bad quality music, which will stay like that for something like 5 seconds after closing the applet.

EXPECTED RESULT

Clicking on the applet should not trigger my headset to switch to "headset" mode.

Maybe have an option in the applet's settings to control whether one wants to see the microphone volume?

Note that "Audio" under System Settings does not have this issue, even though it offers a pretty similar feature set to the applet (because it does not try to show the microphone volume).

SOFTWARE/OS VERSIONS
Windows:
macOS:
Linux/KDE Plasma: Arch Linux
(available in About System)
KDE Plasma Version: 5.26.5
KDE Frameworks Version: 5.101.0
Qt Version: 5.15.8

ADDITIONAL INFORMATION

Comment 1 Nicolas Fella 2023-01-12 14:36:30 UTC

Does the same thing happen when opening pavucontrol?

Comment 2 Nicolas Fella 2023-01-12 14:40:07 UTC

> I own a Plantronics BT600 headset which I use with its USB dongle, and thus I am not connecting it directly to my computer through bluetooth, so no PulseAudio/PipeWire/WirePlumber is involved in this switching.

I don't understand what you mean with that. Everything the audio applet does goes through PulseAudio/PipeWire, there is no direct communication between Plasma and the device, regardless of how it is connected

Comment 3 zsolt 2023-01-12 19:00:37 UTC

(In reply to Nicolas Fella from comment #1)
> Does the same thing happen when opening pavucontrol?

Yes, it does. It happens exactly when opening the app, I don't even need to switch to the Input Devices tab (the one that shows the microphones).

Comment 4 zsolt 2023-01-12 19:04:20 UTC

(In reply to Nicolas Fella from comment #2)
> > I own a Plantronics BT600 headset which I use with its USB dongle, and thus I am not connecting it directly to my computer through bluetooth, so no PulseAudio/PipeWire/WirePlumber is involved in this switching.
> 
> I don't understand what you mean with that. Everything the audio applet does
> goes through PulseAudio/PipeWire, there is no direct communication between
> Plasma and the device, regardless of how it is connected

Sorry for not making this clearer. I meant specifically the switching of the bluetooth audio profiles, between the "headphones" mode (A2DP) and the "headset" mode (mSBC). Since I'm using the dongle, it appears as a separate sound device, and the switching is done automatically by the dongle. Applications such as WirePlumber (with PipeWire) can do pretty much the same thing for headset directly connected through bluetoth, see https://wiki.archlinux.org/title/PipeWire#Automatic_profile_selection .

Comment 5 Nicolas Fella 2023-01-12 22:14:27 UTC

I see, very interesting feature. 

Wireplumber's implementation seems smart enough to ignore monitor streams to not run into this problem, but that doesn't help if its indeed done by the hardware. You could ask the Pipewire people whether there is something that can be done about this, I'm not familiar enough with the lower parts of the audio stack to judge that. From a Plasma POV I don't think there's anything I can do here, short of disabling the volume meter entirely

Comment 6 zsolt 2023-01-13 08:56:07 UTC

(In reply to Nicolas Fella from comment #5)
> From a Plasma POV I don't think there's anything I can do here, short of disabling the volume meter entirely

I have two options in mind:
1. Manual configuration: have a new checkbox in the applet settings to disable the volume meter for all input devices, unchecked by default for compatibility
2. Have some kind of automatic detection in place that based on some device property knows that it's unwise to show the volume meter - though I don't if or how this would be possible

I think the best would be option #1.