[music-dsp] Bandlimited.pdf questions

Paul Chana pav_101 at hotmail.com
Wed Nov 26 09:22:01 EST 2003


hi there,

I've been studying Joe Wright's paper "Synthesising band limited waveforms 
using wavetables" (bandlimited.pdf on musicdsp.com),
and i have a couple of questions:


firstly, to generate the out out of phase sawtooth, can i simply change this 
code:

for(b = 0; b < 4096; b++)
	datap[b] += m * sinetable[(b * partial) % 4096];

to

for(b = 0; b < 4096; b++)
	data[b] += m * sineTable[((b * partial) + PI) % 4096];


or have i oversimplified and missed something? Or does the offset get added 
during interpolation? Can anyone show write some code to show me this????

Next to generate the square wave, i use the formula
sinx + 1/3sin3x + 1/5sin5x...

The way i was looking at the code, i would suggest that i can do

for(a = 0; a < partials; a++)			// sum together the partials for this note.
{
                // CHANGED THIS PART HERE from partial = a+ 1
	partial = a + 3;

	m = cos((float)a * HALFPI / (float)partials); //gibbs
	m *= m; //gibbs

	// reduce the level of the upper partials.
	m /=( float)partial;

	// here we are actually generating the wave table for this frequency
	for(b = 0; b < 4096; b++)
		datap[b] += m * sinetable[(b * partial) % 4096];
}

Third, just to clarify this, what is refered to in the code as a partial is 
the same as the number of harmonics?
Little confused about this because the terminology changes, but i think 
thats right?


Lastly, in the implementation at the end of paper, reference is made to two 
variables :
slide and fm.
Neither of these is defined or commented.

rate*=slide; //slide coeffecient if required
temprate=rate*fm; //frequency modulation if required

My question is what sort of values i should be putting in to these? For 
example does slide go from 0 - 1?

Thanks for the help
Paul

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