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

["Jérôme M. Berger"]

Fons Adriaensen wrote:
> It is never necessary. It it were that would imply that a sound
> card without any gain controls (equivalent to a fixed 0 dB gain)
> would fail in some cases. It doesn't. In fact many PRO cards are
> just like that.
> 
> If you have apps A, B, C with volumes a, b, c you can always
> set the HW gain to unity gain (0dB), and send 
>   
>   s = a * A + b * B + c * C         (1)
> 
> to the soundcard. What would be the advantage of doing what
> PA does, which is
> 
> * m = maximum of a, b, c)
> * Set the master to m,
> * send 
>  
>   s = a/m * A + b/m * B + c/m * C    (2)
>     
> ???
> 
> It can only generate trouble, basically you forfeit any
> headroom the system would have. 
> 
	Actually, that's one point where PA is right (even though it's
wrong on a lot of other points): doing it like (2) avoids amplifying
the quantification noise if the sound card applies the master gain
in analog (or uses higher bit depths internally before the DACs as
some do).

	When cascading amplifiers, it is always better to put the highest
possible gain on the first stages (always leaving enough headroom to
avoid clipping/distortion) so that later stages will not amplify the
noise from the first stages (or so that they will reduce it along
with the signal). The only case when this rule does not hold is when
doing digital processing in floating point (because then the
quantification noise is defined as a proportion of the actual signal
instead of its potential maximum).

		Jerome
-- 
mailto:jeberger at free.fr
http://jeberger.free.fr
Jabber: jeberger at jabber.fr

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