[PD] Anti-aliasing filter

Martin Peach martinrp at vax2.concordia.ca
Wed May 19 16:24:38 CEST 2004

julien.breval at 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.


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