tal-reverb-2-juce/src/Engine/LowShelf.h

   1 /*-----------------------------------------------------------------------------
   2
   3 Kunz Patrick 30.04.2007
   4
   5 A one pole low pass filter.
   6
   7 -----------------------------------------------------------------------------*/
   8
   9 #if !defined(__LowShelf_h)
  10 #define __LowShelf_h
  11
  12 #include "Math.h"
  13
  14 class LowShelf
  15 {
  16 public:
  17         int filterDecibel;
  18
  19         float sampleRate;
  20
  21         float a0, a1, a2;
  22         float b0, b1, b2;
  23
  24         float x0, x1, x2;
  25         float     y1, y2;
  26
  27         float outSample;
  28
  29         float a, w0, q, s, alpha;
  30         float cosValue, sqrtValue;
  31         float vsa;   // Very small amount (Denormal Fix)
  32
  33         float dBgain, freq;
  34
  35         float random;
  36
  37         LowShelf(float sampleRate, int filterDecibel)
  38         {
  39                 this->sampleRate = sampleRate;
  40                 this->filterDecibel = filterDecibel;
  41
  42                 a0 = a1 = a2 = 0.0f;
  43                 b0 = b1 = b2 = 0.0f;
  44
  45                 x0 = x1 = x2 = 0.0f;
  46                 y1 = y2 = 0.0f;
  47
  48                 q = dBgain = freq = 0.0f;
  49
  50                 s = 1.0f;
  51                 vsa= (1.0f/4294967295.0f);   // Very small amount (Denormal Fix)
  52         }
  53
  54         // gain [0..1], q[0..1], freq[0..44100]
  55         inline void tick(float *inSample, float freq, float q, float gain)
  56         {
  57                 gain = filterDecibel - (1.0f - gain) * filterDecibel * 2.0f;
  58                 calcCoefficients(freq, q, gain);
  59
  60                 outSample = b0*x0 + b1*x1 + b2*x2 - a1*y1 - a2*y2;
  61                 outSample = b0*x0 + b1*x1 + b2*x2 - a1*y1 - a2*y2;
  62                 updateHistory(*inSample, outSample);
  63                 *inSample = outSample;
  64         }
  65
  66         inline void calcCoefficients(float freq, float q, float dBgain)
  67         {
  68                 if (this->q != q || this->dBgain != dBgain || this->freq != freq)
  69                 {
  70                         this->dBgain = dBgain;
  71                         this->q = q;
  72                         this->freq = freq;
  73                         w0 = 2.0f * 3.141592653589793f * freq / sampleRate;
  74
  75                         a = sqrtf(pow(10, dBgain/20.0f));
  76                         alpha = sinf(w0)/(2.0f*q);
  77                         q = 1.0f / sqrt((a + 1.0f/a)*(1.0f/s - 1.0f) + 2.0f);
  78
  79                         cosValue = cosf(w0);
  80                         sqrtValue = sqrtf(a);
  81                 }
  82                 b0 =         a * ((a + 1.0f) - (a - 1.0f) * cosValue + 2.0f * sqrtValue * alpha );
  83                 b1 =  2.0f * a * ((a - 1.0f) - (a + 1.0f) * cosValue                           );
  84                 b2 =         a * ((a + 1.0f) - (a - 1.0f) * cosValue - 2.0f * sqrtValue * alpha );
  85                 a0 =              (a + 1.0f) + (a - 1.0f) * cosValue + 2.0f * sqrtValue * alpha;
  86                 a1 =    - 2.0f * ((a - 1.0f) + (a + 1.0f) * cosValue                           );
  87                 a2 =              (a + 1.0f) + (a - 1.0f) * cosValue - 2.0f * sqrtValue * alpha;
  88
  89                 a0 = 1.0f/a0;
  90
  91                 b0 *= a0;
  92                 b1 *= a0;
  93                 b2 *= a0;
  94                 a1 *= a0;
  95                 a2 *= a0;
  96         }
  97
  98         inline void updateHistory(float inSample, float outSample)
  99         {
 100                 x0 = saturate(x1, -0.08f);
 101                 x1 = saturate(x2, 0.05f);
 102                 x2 = saturate(inSample, 0.01f);
 103
 104                 y2 = y1;
 105                 y1 = outSample;
 106         }
 107
 108         inline float saturate(float x, float variation)
 109         {
 110                 return x - 0.002f * (x + variation) * x * x;
 111         }
 112 };
 113
 114 #endif