realoud_lpf

// Copyright 2006, Thomas Scott Stillwell
// All rights reserved.
//
//Redistribution and use in source and binary forms, with or without modification, are permitted 
//provided that the following conditions are met:
//
//Redistributions of source code must retain the above copyright notice, this list of conditions 
//and the following disclaimer. 
//
//Redistributions in binary form must reproduce the above copyright notice, this list of conditions 
//and the following disclaimer in the documentation and/or other materials provided with the distribution. 
//
//The name of Thomas Scott Stillwell may not be used to endorse or 
//promote products derived from this software without specific prior written permission. 
//
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//IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND 
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desc:ReaLoud LP
desc:ReaLoud LP [stillwell]
//tags: dynamics saturation filter
//author: Stillwell

slider1:0<0,100,0.1>Mix (%)
slider3:22000<1,22000>LP Frequency (Hz)
slider4:0.2<0,1>LP Size (1/Q) (0=resonant, 1=dull)
slider5:1<0,1,1{Pre-filter,Post-filter}>Drive Circuit

in_pin:left input
in_pin:right input
out_pin:left output
out_pin:right output

@init

  pi = 3.1415926535;
  halfpi = pi / 2;

@slider

  mix=slider1 / 100;
  drive=slider2 / 100;
  freq=slider3;
  size=slider4;
  prepost=slider5;

  damp=0.01+size*20;
  c = 1/tan($pi*freq/srate);
  fk = 1 / (1 + c*(c+damp));
  fa1 = 2 * (1 - c*c) * fk;
  fa0 = (1 + c*(c-damp)) * fk;
  oldamp=damp;

  mix1 = 1 - mix;

@sample


  dry0 = spl0;
  dry1 = spl1;

  prepost>0.5 ? (
    spl0=min(max(spl0,-1),1);
    spl1=min(max(spl1,-1),1);

    wet0 = sin(dry0 * halfpi);
    wet1 = sin(dry1 * halfpi);

    fd0l = (fk*wet0) - (fa1*fd1l) - (fa0*fd2l);
    fd0r = (fk*wet1) - (fa1*fd1r) - (fa0*fd2r);

    spl0 = mix1 * dry0 + mix * (fd0l + fd1l + fd1l + fd2l);
    spl1 = mix1 * dry1 + mix * (fd0r + fd1r + fd1r + fd2r);
  ) : (
    fd0l = (fk*dry0) - (fa1*fd1l) - (fa0*fd2l);
    fd0r = (fk*dry1) - (fa1*fd1r) - (fa0*fd2r);

    wet0 = fd0l + fd1l + fd1l + fd2l;
    wet1 = fd0r + fd1r + fd1r + fd2r;

    spl0=min(max(spl0,-1),1);
    spl1=min(max(spl1,-1),1);

    wet0 = sin(wet0 * halfpi);
    wet1 = sin(wet1 * halfpi);

    spl0 = mix1 * dry0 + mix * wet0;
    spl1 = mix1 * dry1 + mix * wet1;
  );

  fd2l = fd1l;
  fd2r = fd1r;

  fd1l = fd0l;
  fd1r = fd0r;

  spl0=min(max(spl0,-1),1);
  spl1=min(max(spl1,-1),1);