How to change the ringtone when I am calling someone?
(that beep sound). The default sound is too loud. It is not any of these settings:

I cannot reduce the application overall audio because my calls audio become too low. This is the beep I am using:
- https://www.zedge.net/ringtone/1df6cced-7219-36b6-a779-3885be91c8e7
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I just converted it from .mp3 to .wav and it worked.
It would be very useful to put a warning saying you must to select a .wav file:

Do note that the file selector (QFileDialog) does apply a (non-optional) *.wav filter, making it impossible to select a .mp3 file by mistake. This issue only matters when filling the text field manually. (The "What's This?" message does mention what format is required, but I doubt anybody reads those. I certainly don't.)
I wonder if it wouldn't make more sense to simply disable editing of that text field, and require that the file selector be used. It would also ensure that the file does exist (currently, at least), preventing typos.
I wonder if it wouldn't make more sense to simply disable editing of that text field, and require that the file selector be used. It would also ensure that the file does exist (currently, at least), preventing typos.
I would say that it is just bad forcing to use the GUI. Just putting hint (on the side of Custom ring back tone is more than enough:

Do note that the file selector (QFileDialog) does apply a (non-optional) *.wav filter, making it impossible to select a .mp3 file by mistake.
As you said, the GUI already has this hint. Only the free input form is missing it.