Disable PulseAudio flat volumes to prevent it from pushing volume level to max

[Owen Taylor]

On Thu, 2015-09-17 at 23:26 +0200, Germano Massullo wrote:
> Il 17/09/2015 21:13, Andrew Lutomirski ha scritto:
> > 
> > To clarify: did you get blasted by music or by video conference
> > sounds?  If the music volume got louder, then it sounds like either
> > a
> > straight-up bug in PulseAudio (and a severe and dangerous one at
> > that)
> > or a serious bug in your video conference volume in which it
> > adjusts
> > the volume of streams other than its own.
> > 
> > If you got blasted by video conference sounds, then I'd say it's a
> > serious design flaw in PulseAudio.  PulseAudio should offer an
> > easy-to-configure maximum volume (probably A-weighted power, but
> > peak
> > level works, too, if considerably less well) on a per-output basis
> > with which to protect your ears.
> > 
> > --Andy
> I got blasted from the music because I was not making a conference, I
> only logged into the software, so the music was the only sound I was
> listening to. PulseAudio pushed the master audio level to 100%
> (therefore all applications audio level changed to 100%, due flat-
> volume setting).

I'm not an expert in the subject, but I'm pretty sure this is not how
flat volumes are supposed to work - it doesn't sound like useful
behavior at all!

Experimenting with GNOME, the model presented to the user seems to be:

 - Each application's volume control separate goes from 0-100% of the
   maximum system volume. 
 - Adjusting each application is independent
 - Modifying the system global volume slider proportionally adjusts the
   volume of each application
 - The system global volume slider is always maintained to be at least
   as much as the maximum of any application

 NOTE: The system global volume slider is *not the same as the hardware
       volume and does not represent a multiplication factor for
       application volumes. It's just something that the user can
       drag to change the volume of all applications.

There is danger to the ears if an application assumes that 100% volume
is a safe volume and blindly sets its volume to 100% without user
input. But that only affects that application - one application's
misbehavior never affects another application.

It sounds like KDE ends up implementing a different model, either
intentionally or because of bugs. It's also possible that lower level
bugs (sound card driver, for example) might be making things misbehave.

In general, the fact that pulseaudio is configurable in this area is
going to be the source of almost infinite bug chasing, as applications
and desktop environments are "fixed" for one setting or another. It's
also very easy for people to stop investigating problems and say that
"changing the setting fixed it for me." :-(

- Owen