Hi, Alexandre,
On the one hand, a filter could be designed to approximate what you need, but this sounds like a job for the wavelet transform. A linear filter can't handle the level-dependent changes in iso-sonic curves. In the wavelet domain, you could apply different compression/expansion curves for each subband to approximately invert the equal loudness contours.
The only big problem here is that you need to have a calibrated system to make a real difference. You need to know, when you tell your loudspeaker to output 90 dB at 1000 Hz, it will *be* 90 dB for your listeners (same for all the other frequencies in your composition). Also, the loudness can vary over the listening area, and may depend on reverberation.
If you've already got a multi-band equalizer set up and a microphone to take measurements in some particular listening position, you can already make a decent linear approximation, without anything else.
Chuck
On 1/25/07, Alexandre Quessy listes@sourcelibre.com wrote:
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
PD-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list