sv_filter.cpp

   1 /*
   2   ZynAddSubFX - a software synthesizer
   3
   4   SVFilter.C - Several state-variable filters
   5   Copyright (C) 2002-2005 Nasca Octavian Paul
   6   Author: Nasca Octavian Paul
   7
   8   This program is free software; you can redistribute it and/or modify
   9   it under the terms of version 2 of the GNU General Public License
  10   as published by the Free Software Foundation.
  11
  12   This program is distributed in the hope that it will be useful,
  13   but WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15   GNU General Public License (version 2) for more details.
  16
  17   You should have received a copy of the GNU General Public License (version 2)
  18   along with this program; if not, write to the Free Software Foundation,
  19   Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  20
  21 */
  22
  23 #include <math.h>
  24 #include <stdio.h>
  25 #include <assert.h>
  26
  27 #include "globals.h"
  28 #include "filter_base.h"
  29 #include "sv_filter.h"
  30
  31 void SVFilter::init(float sample_rate, int type, REALTYPE Ffreq, REALTYPE Fq, unsigned char Fstages, float gain)
  32 {
  33   m_sample_rate = sample_rate;
  34   stages = Fstages;
  35   m_type = type;
  36   freq = Ffreq;
  37   q = Fq;
  38   m_gain = 1.0;
  39   m_outgain = 1.0;
  40   needsinterpolation = 0;
  41   firsttime = 1;
  42
  43   if (stages >= MAX_FILTER_STAGES)
  44   {
  45     stages = MAX_FILTER_STAGES;
  46   }
  47
  48   cleanup();
  49   setfreq_and_q(Ffreq,Fq);
  50
  51   m_outgain = dB2rap(gain);
  52   if (m_outgain > 1.0)
  53   {
  54     m_outgain = sqrt(m_outgain);
  55   }
  56 }
  57
  58 void SVFilter::cleanup()
  59 {
  60   int i;
  61
  62   for (i = 0 ; i < MAX_FILTER_STAGES + 1 ; i++)
  63   {
  64     st[i].low = 0.0;
  65     st[i].high = 0.0;
  66     st[i].band = 0.0;
  67     st[i].notch = 0.0;
  68   }
  69
  70   oldabovenq = 0;
  71
  72   abovenq = 0;
  73 }
  74
  75 void SVFilter::computefiltercoefs()
  76 {
  77   par.f = freq / m_sample_rate * 4.0;
  78
  79   if (par.f > 0.99999)
  80   {
  81     par.f = 0.99999;
  82   }
  83
  84   par.q = 1.0 - atan(sqrt(q)) * 2.0 / PI;
  85   par.q = pow(par.q, 1.0 / (stages + 1));
  86   par.q_sqrt = sqrt(par.q);
  87 }
  88
  89 void SVFilter::setfreq(REALTYPE frequency)
  90 {
  91   REALTYPE rap;
  92   int nyquistthresh;
  93
  94   if (frequency < 0.1)
  95   {
  96     frequency = 0.1;
  97   }
  98
  99   rap = freq / frequency;
 100   if (rap < 1.0)
 101   {
 102     rap = 1.0 / rap;
 103   }
 104
 105   oldabovenq = abovenq;
 106   abovenq = frequency > (m_sample_rate / 2 - 500.0);
 107
 108   nyquistthresh = (abovenq ^ oldabovenq);
 109
 110   if (rap > 3.0 || nyquistthresh != 0)
 111   {
 112     // if the frequency is changed fast, it needs interpolation (now, filter and coeficients backup)
 113     if (firsttime == 0)
 114     {
 115       needsinterpolation = 1;
 116     }
 117
 118     ipar = par;
 119   }
 120
 121   freq = frequency;
 122
 123   computefiltercoefs();
 124
 125   firsttime = 0;
 126 }
 127
 128 void SVFilter::setfreq_and_q(REALTYPE frequency,REALTYPE q_)
 129 {
 130   q = q_;
 131
 132   setfreq(frequency);
 133 }
 134
 135 void SVFilter::setq(REALTYPE q_)
 136 {
 137   q = q_;
 138   computefiltercoefs();
 139 }
 140
 141 void SVFilter::settype(int type)
 142 {
 143   m_type = type;
 144
 145   computefiltercoefs();
 146 }
 147
 148 void SVFilter::setgain(REALTYPE dBgain)
 149 {
 150   m_gain = dB2rap(dBgain);
 151   computefiltercoefs();
 152 }
 153
 154 void SVFilter::setstages(int stages_)
 155 {
 156   if (stages_ >= MAX_FILTER_STAGES)
 157   {
 158     stages_ = MAX_FILTER_STAGES - 1;
 159   }
 160
 161   stages=stages_;
 162
 163   cleanup();
 164
 165   computefiltercoefs();
 166 }
 167
 168 void SVFilter::singlefilterout(REALTYPE *smp,fstage &x,parameters &par)
 169 {
 170   int i;
 171   REALTYPE *out=NULL;
 172
 173   switch(m_type)
 174   {
 175   case ZYN_FILTER_SV_TYPE_LOWPASS:
 176     out = &x.low;
 177     break;
 178   case ZYN_FILTER_SV_TYPE_HIGHPASS:
 179     out = &x.high;
 180     break;
 181   case ZYN_FILTER_SV_TYPE_BANDPASS:
 182     out = &x.band;
 183     break;
 184   case ZYN_FILTER_SV_TYPE_NOTCH:
 185     out = &x.notch;
 186     break;
 187   default:
 188     assert(0);
 189     return;
 190   }
 191
 192   for (i = 0 ; i < SOUND_BUFFER_SIZE ; i++)
 193   {
 194     x.low = x.low + par.f * x.band;
 195     x.high = par.q_sqrt * smp[i] - x.low - par.q * x.band;
 196     x.band = par.f * x.high + x.band;
 197     x.notch = x.high + x.low;
 198
 199     smp[i] = *out;
 200   }
 201 }
 202
 203 void SVFilter::filterout(REALTYPE *smp)
 204 {
 205   int i;
 206   REALTYPE x;
 207
 208   if (needsinterpolation != 0)
 209   {
 210     for (i = 0 ; i < SOUND_BUFFER_SIZE ; i++)
 211     {
 212       m_ismp[i] = smp[i];
 213     }
 214
 215     for (i=0 ; i < stages + 1 ; i++)
 216     {
 217       singlefilterout(m_ismp, st[i], ipar);
 218     }
 219   }
 220
 221   for (i = 0 ; i < stages + 1 ; i++)
 222   {
 223     singlefilterout(smp, st[i], par);
 224   }
 225
 226   if (needsinterpolation != 0)
 227   {
 228     for (i = 0 ; i < SOUND_BUFFER_SIZE ; i++)
 229     {
 230       x = i / (REALTYPE)SOUND_BUFFER_SIZE;
 231       smp[i] = m_ismp[i] * (1.0 - x) + smp[i] * x;
 232     }
 233
 234     needsinterpolation = 0;
 235   }
 236
 237   for (i = 0 ; i < SOUND_BUFFER_SIZE ; i++)
 238   {
 239     smp[i] *= m_outgain;
 240   }
 241 }