db volume scaling

[Tim Blechmann]

>>> Hmmmm I might be totally not getting this whole db thing but how is
>>> our current system not intuitive and how is this more intuitive?
> 
>> but to the current system: what does it mean, if you increase the volume
>> from 20% to 40% to 60%? i must admit, i have no idea.
> 
> It means that the volume of the audio stream Amarok is pushing through
> the sound system scales from 20% of its maximum level to 40% of its
> maximum level to 60% of its maximum level.  Not sure why this is
> difficult to figure out.

fortunately this is not the case.
i suppose phonon internally represents the audio data as 32-bit floats
in the range from -1 to 1.
the setting 20% does not mean a range scaled to -0.2 to 0.2 (which would
be braindead from a psychoacoustic point of view), but something else,
since phonon (according to the docs) uses an internal scaling (stevens'
law) to take loudness into account.

>> of course, i can
>> check the phonon sources, but the value itself doesn't tell me
>> _anything_ about the actual amplitudes.
> 
> Neither does the dB scale.  It tells you what the amplitudes are
> relative to each other, but it doesn't tell you what the actual
> amplitude is when the slider is at 0dB.

an amplitude value of 0dB tells me, that the audio data fits to the
range -1 to 1. in the digital domain, this tells me _exactly_, what the
amplitude is.

>> the db scale is well defined and
>> reducing the volume by 10dB in one program sounds the same as in
>> another program or on the amplifier of your speakers.
> 
> So does reducing the volume by 10%.  Phonon has a volume value.  Setting
> it has the same effect regardless of what program is setting it.

that is not the point, the point is, what is the factor internally used?
 it is _not_ 0.1.

but back to psychoacoustics: afaict, amarok uses phonom to create a
linear loudness scale, where a logarithmic loudness scale would be more
appropriate for the human ear (at least for mine).

but i would suggest, you try my patch yourself, preferably in an
audiophile setup (quiet room, good speakers).

best, tim

-- 
tim at klingt.org
http://tim.klingt.org

The first question I ask myself when something doesn't seem to be
beautiful is why do I think it's not beautiful. And very shortly you
discover that there is no reason.
  John Cage.

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