MicroDexed/PluginFx.cpp

/**

   Copyright (c) 2013-2014 Pascal Gauthier.
   Copyright (c) 2013-2014 Filatov Vadim.

   Filter taken from the Obxd project :
     https://github.com/2DaT/Obxd

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA

*/

#define _USE_MATH_DEFINES
#include <math.h>
#include "PluginFx.h"
#include "synth.h"

const float dc = 1e-18;

inline static float tptpc(float& state, float inp, float cutoff) {
  float v = (inp - state) * cutoff / (1 + cutoff);
  float res = v + state;
  state = res + v;
  return res;
}

inline static float tptlpupw(float & state , float inp , float cutoff , float srInv) {
  cutoff = (cutoff * srInv) * M_PI;
  float v = (inp - state) * cutoff / (1 + cutoff);
  float res = v + state;
  state = res + v;
  return res;
}

//static float linsc(float param,const float min,const float max) {
//    return (param) * (max - min) + min;
//}

static float logsc(float param, const float min, const float max, const float rolloff = 19.0f) {
  return ((EXP_FUNC(param * LOG_FUNC(rolloff + 1)) - 1.0f) / (rolloff)) * (max - min) + min;
}

PluginFx::PluginFx() {
  Cutoff = 1;
  Reso = 0;
  Gain = 1;
}

void PluginFx::init(int sr) {
  mm = 0;
  s1 = s2 = s3 = s4 = c = d = 0;
  R24 = 0;

  mmch = (int)(mm * 3);
  mmt = mm * 3 - mmch;

  sampleRate = sr;
  sampleRateInv = 1 / sampleRate;
#if defined(ARM_SQRT_FUNC)
  float rcrate; ARM_SQRT_FUNC(44000 / sampleRate, &rcrate);
#else
  float rcrate = SQRT_FUNC((44000 / sampleRate));
#endif
  rcor24 = (970.0 / 44000) * rcrate;
  rcor24Inv = 1 / rcor24;

  bright = tanf((sampleRate * 0.5f - 10) * M_PI * sampleRateInv);

  R = 1;
  rcor = (480.0 / 44000) * rcrate;
  rcorInv = 1 / rcor;
  bandPassSw = false;

  pCutoff = -1;
  pReso = -1;

  dc_r = 1.0 - (126.0 / sr);
  dc_id = 0;
  dc_od = 0;
}

inline float PluginFx::NR24(float sample, float g, float lpc) {
  float ml = 1 / (1 + g);
  float S = (lpc * (lpc * (lpc * s1 + s2) + s3) + s4) * ml;
  float G = lpc * lpc * lpc * lpc;
  float y = (sample - R24 * S) / (1 + R24 * G);
  return y + 1e-8;
};

inline float PluginFx::NR(float sample, float g) {
  float y = ((sample - R * s1 * 2 - g * s1  - s2) / (1 + g * (2 * R + g))) + dc;
  return y;
}

void PluginFx::process(float *work, int sampleSize) {
  // very basic DC filter
  float t_fd = work[0];
  work[0] = work[0] - dc_id + dc_r * dc_od;
  dc_id = t_fd;
  for (int i = 1; i < sampleSize; i++) {
    t_fd = work[i];
    work[i] = work[i] - dc_id + dc_r * work[i - 1];
    dc_id = t_fd;

  }
  dc_od = work[sampleSize - 1];

  if ( Gain != 1 ) {
    for (int i = 0; i < sampleSize; i++ )
      work[i] *= Gain;
  }

  // don't apply the LPF if the cutoff is to maximum
  if ( Cutoff == 1 )
    return;

  if ( Cutoff != pCutoff || Reso != pReso ) {
    rReso = (0.991 - logsc(1 - Reso, 0, 0.991));
    R24 = 3.5 * rReso;

    float cutoffNorm = logsc(Cutoff, 60, 19000);
    rCutoff = (float)tanf(cutoffNorm * sampleRateInv * M_PI);

    pCutoff = Cutoff;
    pReso = Reso;

    R = 1 - rReso;
  }

  // THIS IS MY FAVORITE 4POLE OBXd filter

  // maybe smooth this value
  float g = rCutoff;
  float lpc = g / (1 + g);

  for (int i = 0; i < sampleSize; i++ ) {
    float s = work[i];
    s = s - 0.45 * tptlpupw(c, s, 15, sampleRateInv);
    s = tptpc(d, s, bright);

    float y0 = NR24(s, g, lpc);

    //first low pass in cascade
    float v = (y0 - s1) * lpc;
    float res = v + s1;
    s1 = res + v;

    //damping
    s1 = atanf(s1 * rcor24) * rcor24Inv;
    float y1 = res;
    float y2 = tptpc(s2, y1, g);
    float y3 = tptpc(s3, y2, g);
    float y4 = tptpc(s4, y3, g);
    float mc = 0.0;

    switch (mmch) {
      case 0:
        mc = ((1 - mmt) * y4 + (mmt) * y3);
        break;
      case 1:
        mc = ((1 - mmt) * y3 + (mmt) * y2);
        break;
      case 2:
        mc = ((1 - mmt) * y2 + (mmt) * y1);
        break;
      case 3:
        mc = y1;
        break;
    }

    //half volume comp
    work[i] = mc * (1 + R24 * 0.45);
  }
}

/*

  // THIS IS THE 2POLE FILTER

  for(int i=0; i < sampleSize; i++ ) {
  float s = work[i];
  s = s - 0.45*tptlpupw(c,s,15,sampleRateInv);
  s = tptpc(d,s,bright);

  //float v = ((sample- R * s1*2 - g2*s1 - s2)/(1+ R*g1*2 + g1*g2));
  float v = NR(s,g);
  float y1 = v*g + s1;
  //damping
  s1 = atanf(s1 * rcor) * rcorInv;

  float y2 = y1*g + s2;
  s2 = y2 + y1*g;

  float mc;
  if(!bandPassSw)
  mc = (1-mm)*y2 + (mm)*v;
  else
  {

  mc =2 * ( mm < 0.5 ?
  ((0.5 - mm) * y2 + (mm) * y1):
  ((1-mm) * y1 + (mm-0.5) * v)
  );
  }

  work[i] = mc;
  }

*/

float PluginFx::getGain(void)
{
  return(Gain);
}