yeah this stuff had me confused for a long while....! it's straightforward in maths to express the sum of two frequencies as the mid freq modulated by a low frequency (half the separation freq) but it's not so straightforward explaining why we can actually HEAR this low frequency even though a fourier transform wouldn't show anything there.....
weird non-linear ears....
Matt
-=-=-=-=-=-=-=-=-=-=-=-=- http://www.loopit.org/ -=-=-=-=-=-=-=-=-=-=-=-=- ----- Original Message ----- From: "Martin Peach" martinrp@vax2.concordia.ca To: julien.breval@tremplin-utc.net Cc: "Al Riley" alrileyuk@yahoo.co.uk; pd-list@iem.at Sent: Wednesday, May 19, 2004 3:24 PM Subject: Re: [PD] Anti-aliasing filter
julien.breval@tremplin-utc.net wrote:
Another solution is to calculate the highest partial that won't produce aliasing, in function of the fundamental. If we call F the fundamental, the k-th partial will have a frequency of
F + k*F
(if you chose another harmonicity system, you may adapt this formula). Therefore the maximum number of computable partials of the F fundamental
is the
integer part of (22050-F)/F. For F = 10 Hz, you can compute 2204 partials For F = 1000 Hz, you can only compute 21 partials The idea, here, is to limit the number of partials to the maximum (you
can
evaluate this maximum in realtime, in function of the fundamental). You
can
either mute the partials that outpass the limit (the most simple
solution) or
not even calculate them.
The effect of ultrasonic partials can be very audible. The sound seems to come from intermodulation distortion in the ear sensors themselves, which is causing lower frequency artefacts. Any calculation to simulate this effect (e.g. multiply together the ultrasonic partials while adding the audible ones) would perhaps add realism to the sound of higher frequency complex tones.
Martin
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