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

[Leonid Isaev]

On Sun, 12 Aug 2012 13:07:32 +0000
Fons Adriaensen <fons at linuxaudio.org> wrote:

> On Sun, Aug 12, 2012 at 02:47:59AM +0200, Tom Gundersen wrote:
> 
> > Argument by authority, nice. Care to elaborate? (Sorry to anyone who
> > is sick of PA, but for once I'm seeing the chance to learn something
> > from one of these threads ;-)).
> 
> No authority needed here, it's just extremely clumsy to use a mixer
> that way, you'd need ten hands. For it means that whenever you want
> to adjust a single channnel you may have to adjust *all* others and
> the master at the same time. 
> 
> > If the problem is too complex to explain in layman terms, that's
> > understandable. However, is the problem one that would be unacceptable
> > in a professional setting (e.g. a recording studio, ...) as it would
> > cause subtle issues. Or is it a problem that I should be able to
> > observe on my crappy speakers at home? If so, what am I listening for?
> > How would I go about reproducing it?
> 
> [1]
> 
> The first and sufficient argument is that is completely *unnecessary*
> to do such things. 
> 
> Assume you have two or more apps producing sound, and one of them (A)
> has its volume set to max, so PA will set the master fader to max.
> Assume things are OK that way (which will probably be the case). 
> 
> Things will still work well when (A) happens to contribute nothing
> (i.e. while it outputs silence). So things will still work well when
> (A) isn't there at all. *There is no need to change anything at all*
> when (A) goes away, even if all others have their volume set to lower
> values.
> 
> [2]
> 
> As to technical arguments, I can try. First thing to know is that
> you shouldn't confuse 'level' (a property of signal), and 'gain'
> (the ratio of two levels, or difference if you think in dB).
> Both are usually expressed in dB, but that doesn't make them the
> same thing. Compare it to time: a instant (epoch) and a duration
> are both expressed in the same units but they are different things.
> For example the sum of two epochs doesn't have any meaning, while
> the sum of two durations has. And if some activity has a duration
> of 40 minutes, that doesn't mean it has to finish at 00:40. 
> 
> Similarly, if an apps has its gain set to -10 dB, that should not
> be taken to imply that it can't output more than -10 dB. 
> 
> On 'real' mixers (digital or analog) you normally have considerable
> 'headroom'. Setting your master fader to -20 dB does not mean you
> can't output more than -20 dB. For digital ones that means that
> they use internally a wider format (more bits) than on the external
> interfaces. So you can actually trade off input gains and master
> gain to some extent. 
> 
> Soundcard mixers are different. The PCM input to the mixer (i.e.
> the samples the SW provides) usually has the same format as the
> AD converter, e.g. 16 or 24 bits. That means that if the master
> is set to e.g. -20 dB, the card can't output any signal that is
> larger than -20 dB (w.r.t. its normal maximum level).
> Which is wrong. Assume you have two or more apps, all of them have
> their volume set to -20 dB. So PA will set the master output to
> -20 dB. Now even if all of these apps are limited to contributing
> -20 dB (but there is no reason why that should be), the sum of
> them can be higher, but your soundcard can't handle that. 
> 
> It all amounts to this: unless the user is using the soundcard's
> 'master' as his global volume control (similar to a volume knob
> on an external amplifier) it should be left at 0 dB. No software
> layer should ever touch it.
> 

So... on my intel AD**** I have PCM and Master knobs (in alsa). Are you saying
that I should set Master to max (-0dB) and control volume through PCM only?

> [3]
> 
> On many soundcards the master fader also controls the level of
> things that PA or any software layer doesn't know about, e.g.
> and external mic input. Which you'd use for karaoke, or to
> hear yourself in your headphones while skyping. That level must
> not depend on how other apps set their volume controls. Again
> the software should not touch the master gain.
> 
> [4]
> 
> You can't apply a soundcard mixer gain change at some exact
> point in a sample stream. So you can't change the master
> gain and change your internal scaling to compensate at
> exactly the same time. There will always be a glitch.
> 



-- 
Leonid Isaev
GnuPG key: 0x164B5A6D
Fingerprint: C0DF 20D0 C075 C3F1 E1BE  775A A7AE F6CB 164B 5A6D
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