[music-dsp] Wavetable/anti aliasing-2

[James W. Morris]

Hi,

I'd like to be able to understand what you've been discussing in the Re: 
[music-dsp] Wavetable synthesis/anti aliasing thread, but I'm not that 
clever:/

However, I've written a user definable wave form where the user inserts 
'vertex's (as many as required) which consist of a horizontal part - degree, 
and, a vertical part - level. The levels are just ramped from one vertex to 
the next to create the shape.

It gives a similiar problem to that being discussed (i think): more complex 
shapes and/or high frequencies cause some vertices to drop out (if 
deg_difference_as_samples < 1, skip to next) which causes a kind of burping 
noise.  (although I'm the type of person who'd try and take advantage of it)

Just to give you some idea of my level of dsp knowledge:  the lowpass filter 
I've written calculates the average level of n samples stored in an array, 
where n is directly proportional to the cutoff frequency.  - ie limited to 
fairly basic maths and algorithms.

What i'm considering for my problem is calculating the highest frequency the 
waveform can operate at (using a minimum noof samples between 2 vertices as 
a guide), and then automatically   creating substitute wave forms for the 
higher frequencies... but the construction of these I'm not quite sure about 
- choosing which vertices can be thrown out without too much loss of 
character.

I probably won't be trying to tackle it for a while though, like >six 
months, giving programming a break, very soon, just after....

Just thought I'd mention it.

James Morris.

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