Fb combfilters: generalize/optimize feed-back comb filters #218
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The next patch will add the users of the new funtion.
To ensure this patch is correct I used the following test-case
maxdel = 10;
N = 7.5; b0 = 1/2; aN = 1/3;
maxerr = abs : max~_;
// Old implementations before this patch
o_fb_comb(maxdel,N,b0,aN) = (+ <: de.delay(maxdel,N-1),_) ~ *(-aN) : !,*(b0) : mem;
o_fb_fcomb(maxdel,N,b0,aN) = (+ <: de.fdelay(maxdel,float(N)-1.0),_) ~ *(-aN) : !,*(b0) : mem;
process = no.noise <:
fi.fb_comb(maxdel,N,b0,aN)
-o_fb_comb(maxdel,N,b0,aN),
fi.fb_fcomb(maxdel,N,b0,aN)
-o_fb_fcomb(maxdel,N,b0,aN)
: par(i,2,maxerr);
compiled with "-a plot.cpp". Result:
$ ./test-plot -n 1000000 | tail -n 1
0 0
This patch makes the source code more understandable and the generated code
more efficient.
For example, the generated code for
process = fi.fb_comb(15,10,1/3,1/4);
before this patch:
// class variables
float fVec0[10];
float fRec0[2];
float fRec1[2];
int fSampleRate;
void compute(int count, FAUSTFLOAT** inputs, FAUSTFLOAT** outputs)
{
FAUSTFLOAT* input0 = inputs[0];
FAUSTFLOAT* output0 = outputs[0];
for (int i0 = 0; i0 < count; i0 = i0 + 1) {
float fTemp0 = float(input0[i0]) - 0.25f * fRec0[1];
fVec0[0] = fTemp0;
fRec0[0] = fVec0[9];
fRec1[0] = fTemp0;
output0[i0] = FAUSTFLOAT(0.33333334f * fRec1[1]);
for (int j0 = 9; j0 > 0; j0 = j0 - 1) {
fVec0[j0] = fVec0[j0 - 1];
}
fRec0[1] = fRec0[0];
fRec1[1] = fRec1[0];
}
}
after this patch:
// class variables
float fRec0[11];
int fSampleRate;
void compute(int count, FAUSTFLOAT** inputs, FAUSTFLOAT** outputs)
{
FAUSTFLOAT* input0 = inputs[0];
FAUSTFLOAT* output0 = outputs[0];
for (int i0 = 0; i0 < count; i0 = i0 + 1) {
fRec0[0] = 0.33333334f * float(input0[i0]) - 0.25f * fRec0[10];
output0[i0] = FAUSTFLOAT(fRec0[1]);
for (int j0 = 10; j0 > 0; j0 = j0 - 1) {
fRec0[j0] = fRec0[j0 - 1];
}
}
}
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If this PR is accepted, I'll try to do more similar changes (fbcombfilter, allpass_comb, and ff_comb).