On 05/30, Dario Sanfilippo wrote:
>
> > And. It seems that the implementation above is "equal" to
> >
> > lpbi(cf) = fi.tf2s(0,0,1, 1/.707, 1, 2*ma.PI/ma.SR * cf);
> >
> > ?
> >
> > or simply
> >
> > lpbi(cf) = resonlp(cf, .707, 1);
> >
> > no ?
> >
>
> I must be doing something wrong with fi.tf2f but I get no response when
> testing it like this:
>
> process = f2.lpbi(1000, au.dirac),
>
> (au.dirac : fi.tf2s(0,0,1, 1/.707, 1, 2*ma.PI/ma.SR * 1000)),
^^^^^^
typo. please try
fi.tf2s(0,0,1, 1/.707, 1, 2*ma.PI * 1000)
> (au.dirac : fi.resonlp(1000, .707, 1));
btw, you could write
process = au.dirac <:
f2.lpbi(1000),
fi.tf2s(0,0,1, 1/.707, 1, 2*ma.PI * 1000),
i.resonlp(1000, .707, 1);
this looks more simple. and au.dirac is os.impulse ;)
> On the other hand, the impulse response of f2.lpbi and fi.resonlp are
> identical:
I think tf2s() should have the same response if you remove "/ma.SR"...
> Perhaps the zero-delay feedback design in Zavalishin is not in the Faust
> filters and it could be integrated. He claims that such filters, even at
> orders higher than 1 or 2, are more stable in time-variant configurations
> than the others.
If you want a second order zdf please consider the code below. I did some
naive non-scientific tests and to me it really works better than even tf2snp
when modulated.
Oleg.
-------------------------------------------------------------------------------
// http://www.cytomic.com/files/dsp/SvfLinearTrapOptimised2.pdf
import("stdfaust.lib");
svf = environment {
svf(T,F,Q,G) = tick ~ (_,_) : !,!,_,_,_ : si.dot(3, mix)
with {
tick(ic1eq, ic2eq, v0) =
2*v1 - ic1eq,
2*v2 - ic2eq,
v0, v1, v2
with {
v1 = ic1eq + g *(v0-ic2eq) : /(1 + g*(g+k));
v2 = ic2eq + g * v1;
};
A = pow(10.0, G / 40.0);
g = tan(F * ma.PI / ma.SR) : case {
(7) => /(sqrt(A));
(8) => *(sqrt(A));
(t) => _;
} (T);
k = case {
(6) => 1/(Q*A);
(t) => 1/Q;
} (T);
mix = case {
(0) => 0, 0, 1;
(1) => 0, 1, 0;
(2) => 1, -k, -1;
(3) => 1, -k, 0;
(4) => 1, -k, -2;
(5) => 1, -2*k, 0;
(6) => 1, k*(A*A-1), 0;
(7) => 1, k*(A-1), A*A-1;
(8) => A*A, k*(1-A)*A, 1-A*A;
} (T);
};
lp(f,q) = svf(0, f,q,0);
bp(f,q) = svf(1, f,q,0);
hp(f,q) = svf(2, f,q,0);
notch(f,q) = svf(3, f,q,0);
peak(f,q) = svf(4, f,q,0);
ap(f,q) = svf(5, f,q,0);
bell(f,q,g) = svf(6, f,q,g);
ls(f,q,g) = svf(7, f,q,g);
hs(f,q,g) = svf(8, f,q,g);
};
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