db volume scaling

[Jeff Mitchell]

On Tue, 09 Jun 2009 16:04:00 +0200, Tim Blechmann <tim at klingt.org> wrote:
>> 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.

No idea.  There are many ways you can represent it.  0 to 1.  0 to 10. 
-123 to -38.  The range doesn't really matter.

> 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.

Well, going on your supposition that phonon uses -1 to 1, 20% would
therefore be -0.6.  40% would be -0.2.  50% would be 0.  Why on earth would
it mean a range scaled -0.2 to 0.2?

> 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.

You can always make the audio data fit in the range -1 to 1.  Just adjust
your scale to fit the audio.  But 0dB still won't tell you what the
amplitude is.  It will tell you what Amarok's relative amplitude is,
relative to the amount of values it can set for volume.

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

Why does it matter?  I would imagine it takes whatever the range is and
multiplies it by the percentage value, then adds that to the bottom of the
range.

> 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).

No need.  I've used programs with logarithmic volume sliders before.  I
dislike them.  So do, I would imagine, the vast majority of users (many of
whom might not understand such a scale, much less like it).

If you're an audiophile, I imagine you have an external speaker and/or
headphone amplifier.  Why not just use the line out of your computer and
adjust the audio from your amplifier?  Why is this Amarok's problem?

--Jeff