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/* 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;
};
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