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// WARNING: This a "legacy example based on a deprecated library". Check filter.lib
// for more accurate examples of filter functions
declare name "lowboost";
declare version "1.0";
declare author "Grame";
declare license "BSD";
declare copyright "(c)GRAME 2006";
//------------------------------------------------------------------
// DAFX, Digital Audio Effects (Wiley ed.)
// chapter 2 : filters
// section 2.3 : Equalizers
// page 53 : second order shelving filter design
//------------------------------------------------------------------
import("stdfaust.lib");
//------------------- low-frequency shelving boost (table 2.3) --------------------
V0(g) = pow(10,g/20.0);
K(fc) = tan(ma.PI*fc/ma.SR);
square(x) = x*x;
denom(fc) = 1 + sqrt(2)*K(fc) + square(K(fc));
lfboost(fc, g) = fi.TF2((1 + sqrt(2*V0(g))*K(fc) + V0(g)*square(K(fc))) / denom(fc),
2 * (V0(g)*square(K(fc)) - 1) / denom(fc),
(1 - sqrt(2*V0(g))*K(fc) + V0(g)*square(K(fc))) / denom(fc),
2 * (square(K(fc)) - 1) / denom(fc),
(1 - sqrt(2)*K(fc) + square(K(fc))) / denom(fc));
//------------------------------ User Interface -----------------------------------
freq = hslider("[1]freq [unit:Hz][style:knob]", 1000, 20, 20000, 0.1);
gain = hslider("[2]gain [unit:dB][style:knob]", 0, -20, 20, 0.1);
//----------------------------------- Process -------------------------------------
process = vgroup("low-freq shelving boost", lfboost(freq,gain));
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