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Band Limited waveforms my way

Type : classic Sawtooth example
References : Posted by Anton Savov (antto mail bg)

Notes :
This is my C++ code for generating a single cycle of a Sawtooth in a table
normaly i create my "fundamental" table big enough to hold on around 20-40Hz in the current Sampling rate
also, i create the table twice as big, i do "mip-maps" then
so the size should be a power of two, say 1024 for 44100Hz = 44100/1024 = ~43.066Hz
then the mip-maps are with decreasing sizes (twice) 512, 256, 128, 64, 32, 16, 8, 4, and 2

if the "gibbs" effect is what i think it is - then i have a simple solution
here is my crappy code:


Code :
int sz = 1024; // the size of the table
int i = 0;
float *table; // pointer to the table
double scale = 1.0;
double pd; // phase
double omega = 1.0 / (double)(sz);

while (i < sz)
{
double amp = scale;
double x = 0.0; // the sample
double h = 1; // harmonic number (starts from 1)
double dd; // fix high frequency "ring"
pd = (double)(i) / (double)(sz); // calc phase
double hpd = pd; // phase of the harmonic
while (true) // start looping for this sample
{
if ((omega * h) < 0.5) // harmonic frequency is in range?
{
dd = cos(omega * h * 2 * pi);
x = x + (amp * dd * sin(hpd * 2 * pi));
h = h + 1;
hpd = pd * h;
amp = 1.0 / h;
}
else { break; }
}
table[i] = x;
++i;
}

the peaks are around +/- 0.8
a square can be generated by just changing h = h+2; the peaks would be +/- 0.4

any bugs/improvements?



Comments


Added on : 22/06/09 by antto [AT] mail [DOT] bg
Comment :
excuse me, there is a typo

amp = scale / h;




Added on : 20/09/09 by antto mail bg
Comment :
for even smoother edges:
dd = cos(sin(omega * h * pi) * 0.5 * pi);
no visual ringing, smooth waveform




Added on : 25/09/09 by antto mail bg
Comment :
to get +/- 1.0 amplitude: scale = 1.25



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