[arch-general] OT: [arch-dev-public] polkit package upgrade patch

[Ralf Mardorf]

On Sun, 2012-08-12 at 03:06 +0200, Ralf Mardorf wrote:
> On Sun, 2012-08-12 at 02:43 +0200, Tom Gundersen wrote:
> > On Sun, Aug 12, 2012 at 1:23 AM, Fons Adriaensen <fons at linuxaudio.org> wrote:
> > > If that is true it is completely wrong from the start. Because
> > > that setup can't be maintained when a second app starts playing
> > > which can happen at any time. Suppose that first (single) app has
> > > its volume set to some low value, and PA uses the soundcard PCM
> > > gain control to achieve that as you claim it does. Now suddenly
> > > there's a second app which wants a higher level. The only way to
> > > achieve that is to raise the hardware gain - you can't compensate
> > > for a low setting there by sending a louder signal, it would just
> > > clip. So PA now has to adjust the hardware gain and at the same
> > > time start scaling down the output from the first app.
> > > It's impossible to do that in any acceptable way.
> > 
> > That's how it works. I have not noticed any problems. How would the
> > problems manifest themselves? I'm not an audio expert by any stretch
> > of the imagination, but I think even I would be able to notice
> > skipping, clipping, noise, ... What should I be listening for?
> 
> It only can work without clipping, if first the volume is lowered with
> more headroom than needed, because you can't know how much headroom you
> exactly need and then the second volume will be raised until an equal
> level is reached and this step by step. But how does PA know at what
> step the level is equal, when the audio signal isn't a constant tone?
> Poettering expect a perfect control values to dB(FS) mapping?! You at
> least will hear skipping. Or else, Poettering add at the end of the
> chain a hardcore multi-band compression, which would be very audible and
> unwanted too.

This is the way how to lower one and to raise another volume for just
one signal to keep the loudness, by getting audible steps. But there is
a second signal, it's unknown, any automation would be very audible.
 
> > > Simple fact is that most soundcards, even if they have a 'mixer',
> > > can't mix PCM signals (i.e. signals from the software) - they can
> > > mix in a CD player, or an external mic input etc.). So for anything
> > > coming from the system there is just one path, which has two controls,
> > > the 'PCM' and the 'master'. The only way to correctly use them if
> > > there if there is software mixing is to set them once to their
> > > correct values (which may depend on what is connected externally),
> > > and them leave them alone and do the rest in software.
> > 
> > So that's apparently not how it is done in PA. Why must it be done in
> > this way? How can I verify that there is a problem?
> 
> The analog output level has to fit to the input of your amplifier, to
> reduce noise and to avoid distortion.
> 
> > > 'A lot of meta-information' LOL. It will provide some usually
> > > meaningless and inconsistent names of controls, their min and
> > > max values, and if you're extremely lucky maybe some indication
> > > mapping control values to dB, which may or may not be correct
> > > (and if it isn't that's not ALSA's fault, it just crappy and
> > > undocumented harware). All of that is visible in alsamixer.
> > 
> > Yes, this is exactly what PA uses. ALAS just displays it without using it.
> 
> So PA does use Voodoo?!