-
-/* Expander unit. */
-
-/* This is pretty much the same as compressor.dsp, but here the given ratio is
- applied to *attenuate* levels *below* the threshold. */
-
-declare name "expander -- expander/noise gate unit";
-declare author "Albert Graef";
-declare version "1.0";
-
-import("music.lib");
-
-/* Controls. */
-
-exp_group(x) = hgroup("1-expander", x);
-env_group(x) = vgroup("2-envelop", x);
-gain_group(x) = vgroup("3-gain", x);
-
-ratio = exp_group(nentry("ratio", 2, 1, 20, 0.1));
-threshold = exp_group(nentry("threshold", -40, -96, 10, 0.1));
-knee = exp_group(nentry("knee", 3, 0, 20, 0.1));
-
-attack = env_group(hslider("attack", 0.001, 0, 1, 0.001)) : max(1/SR);
-release = env_group(hslider("release", 0.1, 0, 10, 0.01)) : max(1/SR);
-
-gain(x) = attach(x, x : gain_group(hbargraph("gain", -96, 0)));
-
-t = 0.1;
-g = exp(-1/(SR*t));
-env = abs : *(1-g) : + ~ *(g);
-rms = sqr : *(1-g) : + ~ *(g) : sqrt;
-sqr(x) = x*x;
-
-env2(x,y) = max(env(x),env(y));
-
-expand(env) = level*(1-r)
-with {
- level = env : h ~ _ : linear2db : (threshold+knee-_) : max(0)
- with {
- h(x,y) = f*x+(1-f)*y with { f = (x<y)*ga+(x>=y)*gr; };
- ga = exp(-1/(SR*attack));
- gr = exp(-1/(SR*release));
- };
- p = level/(knee+eps) : max(0) : min(1) with { eps = 0.001; };
- r = 1-p+p*ratio;
-};
-
-process(x,y) = (g*x,g*y)
-with {
- g = env2(x,y) : expand : gain : db2linear;
-};