qompander.lib

declare name 		"qompander";
declare version 	"1.3";
declare author 		"Bart Brouns";
declare license 	"GNU 3.0";
declare copyright 	"(c) Bart Brouns 2014";
declare credits		"ported from qompander in pd by Katja Vetter";
declare see		"http://www.katjaas.nl/compander/compander.html";
declare additional	"filter coefficients by Olli Niemitalo";

//-----------------------------------------------
// imports
//-----------------------------------------------

import ("effect.lib");


//-----------------------------------------------
// the DSP
//-----------------------------------------------

magnitude = (threshold):db2linear;
exponent = log(magnitude)/log(sin(factor*magnitude*PI/2));

// to go from puredata biquad coefficients to max/msp and faust notation: the first two parameters are negated and put last
olli1(x) = x:		tf2(0.161758, 0, -1, 0, -0.161758):tf2(0.733029, 0, -1, 0, -0.733029):tf2(0.94535 , 0, -1, 0, -0.94535 ):tf2(0.990598, 0, -1, 0, -0.990598);
olli2(x) = x:mem:	tf2(0.479401, 0, -1, 0, -0.479401):tf2(0.876218, 0, -1, 0, -0.876218):tf2(0.976599, 0, -1, 0, -0.976599):tf2(0.9975  , 0, -1, 0, -0.9975  );

pyth(x) = sqrt((olli1(x)*olli1(x))+(olli2(x)*olli2(x))):max(0.00001):min(100); //compute instantaneous amplitudes
attackDecay(x) = pyth(x) :amp_follower_ud(attack/1000,release/1000);
mapping(x) = attackDecay(x) : ((sin((min(1/factor)*(factor/4)) * (2*PI)): max(0.0000001):min(1),exponent) : pow );
qompander(x,factor,threshold,attack,release) = (mapping(x) / attackDecay(x))<: (_,olli1(x):*),(_,olli2(x):*):+:_*(sqrt(0.5));

//process(x) = qompander(x,factor,threshold,attack,release);