
Bandlimited waveforms...
References : Posted by Paul Kellet
Notes : (Quoted from Paul's mail)
Below is another waveform generation method based on a train of sinc functions (actually an alternating loop along a sinc between t=0 and t=period/2).
The code integrates the pulse train with a dc offset to get a sawtooth, but other shapes can be made in the usual ways... Note that 'dc' and 'leak' may need to be adjusted for very high or low frequencies.
I don't know how original it is (I ought to read more) but it is of usable quality, particularly at low frequencies. There's some scope for optimisation by using a table for sinc, or maybe a a truncated/windowed sinc?
I think it should be possible to minimise the aliasing by fine tuning 'dp' to slightly less than 1 so the sincs join together neatly, but I haven't found the best way to do it. Any comments gratefully received.
Code : float p=0.0f; //current position
float dp=1.0f; //change in postion per sample
float pmax; //maximum position
float x; //position in sinc function
float leak=0.995f; //leaky integrator
float dc; //dc offset
float saw; //output
//set frequency...
pmax = 0.5f * getSampleRate() / freqHz;
dc = 0.498f/pmax;
//for each sample...
p += dp;
if(p < 0.0f)
{
p = p;
dp = dp;
}
else if(p > pmax)
{
p = pmax + pmax  p;
dp = dp;
}
x= pi * p;
if(x < 0.00001f)
x=0.00001f; //don't divide by 0
saw = leak*saw + dc + (float)sin(x)/(x); 
Comments
Added on : 22/09/04 by sinewave[ AT ]chello[ DOT ]se Comment : Hi,
Has anyone managed to implement this in a VST?
If anyone could mail me and talk me through it I'd be very grateful. Yes, I'm a total newbie and yes, I'm after a quickfix solution...we all have to start somewhere, eh?
As it stands, where I should be getting a sawtooth I'm getting a fullon and inaudible signal...!
Even a small clue would be nice.
Cheers,
A
Added on : 01/01/12 by druidbloke[ AT ]yahoo[ DOT ]co[ DOT ]uk Comment : this sounds quite nice, maybe going to use it an LV 2 plugin
Added on : 17/01/16 by pvdmeer [atorsomething] gmail [point] com Comment : this is really amazing, and easily hacked into a lutbased algo. i'll try windowing it too, but it already looks like aliasing is well within acceptable levels.

Add your own comment
Comments are displayed in fixed width, no HTML code allowed! 



