[PD] Re: buzz~ (more)www.ccrma.edu/~stilti/papers/blit.pdf

Frank Barknecht fbar at footils.org
Sun Oct 26 16:12:53 CET 2003

Larry Troxler hat gesagt: // Larry Troxler wrote:

> On Sunday 26 October 2003 09:13, Larry Troxler wrote:
> > On Friday 24 October 2003 15:12, Frank Barknecht wrote:
> > > Yes, you're right, it behaves that way. It might very well be that
> > > there indeed is a bug hidden (although it still makes interesting
> > > sounds... ;)
> >
> > Frank, I replaced the formula  with the one in this paper:
> >
> > www.ccrma.www/~stilti/papers/blit.pdf
> >
> That's www-ccrma.stanford.edu/~stilti/papers/blit.pdf 

Here it's in $HOME/audio/doc/blit.pdf ;)

Did you alter the C or the flext version? Maybe it also would be useful
to write this as a SndObj object. SndObj includes a Buzz opcode, but
last time I looked it was generating strange sound, probably because
of rounding errors (It uses table lookups for sin/cos generation).

Well, anyway I'd love to test your code (lazy me)

> Some details I've found, that you can see by looking at the summation form: N 
> is actually the number of harmonics plus one, so that you need N=2 to 
> generate a sinusoid.  Also, the amplitude of the fundamental is scaled by a, 
> which maybe is not very intuitive. I would more expect the fundamental to 
> stay constant and have the other partial amplitudes relative to that (in 
> which case you could just multiply the formula by 1/a). But maybe we should 
> see how csound does it.
> Other thoughts:
> (o) It would be nice if the a parameter could be a DSP signal as well.

Yes, but it will however make it more expensive, because you cannot
precalculate several of the variables anymore. 

> (o) I didn't bother with the theta (initial phase) parameter that's used in 
> the formula - I just set it to zero and didn't compute it. I think it's only 
> usefull if the output is then nonlinearized of if FM is used on it, right?

I think, a mean of resetting it (for oscillator sync) would still be useful.

> (o) Would it make sense to have a version that takes input from an external  
> phasor, rather than using one internally? In this way the computation would 
> be reduced when using a few of these to generate a complete spectrum as is 
> described in the paper.

Yes, I think this would make sense, although I didn't read the blit
paper for some time now.

 Frank Barknecht                               _ ______footils.org__

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