[PD] isosonic curves : level the perceptual loudness of different pitches

[Alexandre Quessy]

Hi all,

I would like to create an abstraction to adjust the amplitude of
synthetic sounds according to the ear sensitivity. At a given
amplitude, we hear the notes in the middle range louder than the high
and low notes. This perceptual property of the audition can be
somewhat undesired in a musical work. (in my opinion at least)

The equal lines of actual amplitude of notes that seem to have the
same loudness are called "isosonic curves". Here are 2 different
graphics of these curves :

http://www.multimedia.uqam.ca/cours/audio/images/diag/sonpsy_isoson.gif
http://www.comm.uqam.ca/GRAM/illu/mus/nature/CourbeDIsosonie.GIF

A few links that might give you a few hint for the calculations :

http://en.wikipedia.org/wiki/DB%28A%29
http://en.wikipedia.org/wiki/Weighting_filter
http://en.wikipedia.org/wiki/Stevens%27_power_law

Anyone would have a formula or a table containing data that could help
me to calculate this ? For instance, we would be able to generate sine
waves of any frequencies that would be perceived as having the same
intensity for all of them, by changing their amplitude according to
this leveling formula . This way, we could hear our low freq notes as
much as the middle ones. Very valuable. :)

Thanks !
-- 
Alexandre Quessy
http://alexandre.quessy.net