Re: [LAD] Floating point processing and high dynamic range audio

Excerpts from Philipp Überbacher's message of 2010-07-22 03:16:00 +0200:
> Excerpts from fons's message of 2010-07-22 02:24:04 +0200:
> > On Thu, Jul 22, 2010 at 01:05:01AM +0200, Philipp Überbacher wrote:
> >
> > > I think the word loudness is a problem here. Afaik it usually refers to
> > > how it is perceived, and twice the amplitude doesn't mean twice the
> > > perceived loudness. It may mean twice the sound pressure level, energy,
> > > or intensity (if we ignore analogue anomalies, as you wrote in some other
> > > answer).
> >
> > Subjective loudness is a very complex thing, depending on the
> > spectrum, duration, and other aspects of the sound, and also
> > on circumstances not related to the sound itself.
> >
> > For mid frequencies and a duraion of one second, the average
> > subjective impression of 'twice as loud' seems to correspond
> > to an SPL difference of around +10 dB.
>
> I had a brief look at the section about loudness in musimathics and it
> mentions 10 dB based on the work of Stevens, S.S. 1956,
> "Calculation of the Loudness of Complex Noise" and 6 dB based on
> Warren, R. M. 1970,
> "Elimination of Biases in Loudness Judgments for Tones.".
> I think I've encountered the 6 dB more often in texts, which doesn't
> mean it's closer to the truth, if that's possible at all.
> Knowing a 'correct' number would be nice for artists and sound
> engineers, but if it varies wildly from person to person, as Gareth Loy
> suggests (no idea where he bases this on) then this simply isn't
> possible. Picking any number within or around this range is probably as
> good as any other.
>
> > I often wondered what criterion we use to determine which
> > objective SPL difference sounds as 'twice as loud'. We don't
> > have any conscious numerical value (there may be unconscious
> > ones such as the amount of auditory nerve pulses, or the amount
> > of neural activity), so what it this impression based on ?
> >
> > The only thing I could imagine is some link with the subjective
> > impression of a variable number of identical sources. For example
> > two people talking could be considered to be 'twice as loud' as
> > one. But that is not the case, the results don't fit at all (it
> > would mean 3 dB instead of 10).
>
> I never thought about that to be honest. It's immensely complex. It
> might have to do with each persons hearing capabilities, for example the
> bandwidth of loudness perception or the smallest discernible loudness
> difference. If it really is very different from person to person, then
> an explanation that takes the different hearing capabilities into
> account could be sensible, don't you think?

I did find some more approaches to the problem, but those are just
ideas. From my personal experience I have to say that I have a very hard
time saying when something is twice as loud. A musically well trained
person might have an easier time, I wouldn't know, but for me twice as
loud is something that is very vague. This might already explain the
large deviation between subjects as described in musimathics. It lead me
to another idea though, the evolutionary perspective. Evolutionary it
likely never was important whether a sound is twice as loud. The only
situation I can imagine where judging loudness probably was important
is judging distances. How far is the animal I can't see, be it prey or
predator, away from me? We know that this takes more than the SPL into
account, and 'twice as loud' doesn't have relevance in this context. So
maybe the loudness perception is linked with spatialization.

My other ideas are rather stupid, just ways to get the right numbers for
your two person idea.
I simply used ln instead of log and got 7, but that's not even Neper and
has no relevance.

The other idea of that kind is to assume a field quantity, which would
result in 6 dB. I'm still easily confused about 10*log and 20*log, but I
think 20*log is usually used for sound pressure, but maybe not for
psychoacoustic effects.

-- 
Regards,
Philipp
--
"Wir stehen selbst enttäuscht und sehn betroffen / Den Vorhang zu und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan
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