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

   1 /*
   2         ==============================================================================
   3         This file is part of Tal-Reverb by Patrick Kunz.
   4
   5         Copyright(c) 2005-2009 Patrick Kunz, TAL
   6         Togu Audio Line, Inc.
   7         http://kunz.corrupt.ch
   8
   9         This file may be licensed under the terms of of the
  10         GNU General Public License Version 2 (the ``GPL'').
  11
  12         Software distributed under the License is distributed
  13         on an ``AS IS'' basis, WITHOUT WARRANTY OF ANY KIND, either
  14         express or implied. See the GPL for the specific language
  15         governing rights and limitations.
  16
  17         You should have received a copy of the GPL along with this
  18         program. If not, go to http://www.gnu.org/licenses/gpl.html
  19         or write to the Free Software Foundation, Inc.,
  20         51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  21         ==============================================================================
  22  */
  23
  24
  25 #if !defined(__Filter_h)
  26 #define __Filter_h
  27
  28 #include "Math.h"
  29
  30 class Filter
  31 {
  32 private:
  33         float f, k, p, scale, r, x;
  34         float y1, y2, y3, y4, oldx, oldy1, oldy2, oldy3;
  35         float fCutoff, fActualCutoff;
  36         float Pi;
  37
  38         float sampleRateFactor;
  39
  40 public:
  41
  42         Filter(float sampleRate)
  43         {
  44                 Pi = 3.141592653f;
  45                 y1 = y2 = y3 = y4 = oldx = oldy1 = oldy2 = oldy3 = 0.0f;
  46
  47                 if (sampleRate <= 0.0f) sampleRate = 44100.0f;
  48
  49                 sampleRateFactor= 44100.0f / sampleRate;
  50                 if (sampleRateFactor > 1.0f)
  51                         sampleRateFactor = 1.0f;
  52
  53                 fActualCutoff = -1.0f;
  54         }
  55
  56         inline float process(float input, float fCutoff, float fRes, bool highPass)
  57         {
  58                 if (fCutoff != fActualCutoff)
  59                 {
  60                         fActualCutoff = fCutoff;
  61                         fCutoff *= sampleRateFactor;
  62                         updateValues(fCutoff * fCutoff);
  63                 }
  64                 x = input;
  65
  66                 // Four cascaded onepole filters (bilinear transform)
  67                 y1 = (x + oldx) * p - k * y1;
  68                 y2 = (y1 + oldy1) * p - k * y2;
  69
  70                 // Save values
  71                 oldx = x;
  72                 oldy1 = y1;
  73                 if (highPass) input = input - y2;
  74                 else input = y2;
  75                 return input;
  76         }
  77
  78         void updateValues(float fCutoff)
  79         {
  80                 // Filter section MOOG VCF
  81                 // CSound source code, Stilson/Smith CCRMA paper.
  82                 f = fCutoff;                                                                            // [0 - 1]
  83                 k = 3.6f * f - 1.6f * f * f - 1.0f;                                     // (Empirical tunning) /// !!! original (convex)
  84
  85                 p = (k + 1.0f) * 0.5f;                                                      // scale [0, 1]
  86                 scale = expf((1.0f - p) * 1.386249f);                           // original
  87         }
  88 };
  89 #endif