1declare name "lowboost"; 2declare version "1.0"; 3declare author "Grame"; 4declare license "BSD"; 5declare copyright "(c)GRAME 2006"; 6 7//------------------------------------------------------------------ 8// DAFX, Digital Audio Effects (Wiley ed.) 9// chapter 2 : filters 10// section 2.3 : Equalizers 11// page 53 : second order shelving filter design 12//------------------------------------------------------------------ 13 14import("music.lib"); 15 16 17//------------------- low-frequency shelving boost (table 2.3) -------------------- 18 19V0(g) = pow(10,g/20.0); 20K(fc) = tan(PI*fc/SR); 21square(x) = x*x; 22denom(fc) = 1 + sqrt(2)*K(fc) + square(K(fc)); 23 24lfboost(fc, g) = TF2( (1 + sqrt(2*V0(g))*K(fc) + V0(g)*square(K(fc))) / denom(fc), 25 2 * (V0(g)*square(K(fc)) - 1) / denom(fc), 26 (1 - sqrt(2*V0(g))*K(fc) + V0(g)*square(K(fc))) / denom(fc), 27 2 * (square(K(fc)) - 1) / denom(fc), 28 (1 - sqrt(2)*K(fc) + square(K(fc))) / denom(fc) 29 ); 30 31 32//------------------------------ User Interface ----------------------------------- 33 34freq = hslider("freq", 1000, 20, 20000, 0.1); 35gain = hslider("gain (db)", 0, -20, 20, 0.1); 36 37 38//----------------------------------- Process ------------------------------------- 39 40process = vgroup("low-freq shelving boost", lfboost(freq,gain)); 41 42