apps/plugins/pdbox/PDa/extra/equalizer.c

   1 /* (C) Guenter Geiger <geiger@epy.co.at> */
   2
   3
   4 /*
   5
   6  These filter coefficients computations are taken from
   7  http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt
   8
   9  written by Robert Bristow-Johnson
  10
  11 */
  12
  13 #ifdef ROCKBOX
  14 #include "plugin.h"
  15 #include "../../pdbox.h"
  16 #include "../src/m_pd.h"
  17 #include "math.h"
  18 #include "filters.h"
  19 #else /* ROCKBOX */
  20 #include "../src/m_pd.h"
  21 #ifdef NT
  22 #pragma warning( disable : 4244 )
  23 #pragma warning( disable : 4305 )
  24 #endif
  25 #include <math.h>
  26 #include "filters.h"
  27 #endif /* ROCKBOX */
  28
  29
  30 /* ------------------- equ ----------------------------*/
  31 static t_class *equ_class;
  32
  33 void equ_bang(t_rbjfilter *x)
  34 {
  35      t_atom at[5];
  36      t_float omega = e_omega(x->x_freq,x->x_rate);
  37      t_float alpha = e_alpha(x->x_bw*0.01,omega);
  38      t_float b0 = 1 + alpha*e_A(x->x_gain);
  39      t_float b1 = -2.*cos(omega);
  40      t_float b2 = 1 - alpha*e_A(x->x_gain);
  41      t_float a0 = 1 + alpha/e_A(x->x_gain);
  42      t_float a1 = -2.*cos(omega);
  43      t_float a2 = 1 - alpha/e_A(x->x_gain);
  44
  45 /*      post("bang %f %f %f",x->x_freq, x->x_gain, x->x_bw);*/
  46
  47      if (!check_stability(-a1/a0,-a2/a0,b0/a0,b1/a0,b2/a0)) {
  48        post("equ: filter unstable -> resetting");
  49        a0=1.;a1=0.;a2=0.;
  50        b0=1.;b1=0.;b2=0.;
  51      }
  52
  53      SETFLOAT(at,-a1/a0);
  54      SETFLOAT(at+1,-a2/a0);
  55      SETFLOAT(at+2,b0/a0);
  56      SETFLOAT(at+3,b1/a0);
  57      SETFLOAT(at+4,b2/a0);
  58
  59      outlet_list(x->x_obj.ob_outlet,&s_list,5,at);
  60 }
  61
  62
  63 void equ_float(t_rbjfilter *x,t_floatarg f)
  64 {
  65      x->x_freq = f;
  66      equ_bang(x);
  67 }
  68
  69
  70 static void *equ_new(t_floatarg f,t_floatarg g,t_floatarg bw)
  71 {
  72     t_rbjfilter *x = (t_rbjfilter *)pd_new(equ_class);
  73
  74     x->x_rate = 44100.0;
  75     outlet_new(&x->x_obj,&s_float);
  76     floatinlet_new(&x->x_obj, &x->x_gain);
  77     floatinlet_new(&x->x_obj, &x->x_bw);
  78     if (f > 0.) x->x_freq = f;
  79     if (bw > 0.) x->x_bw = bw;
  80     if (g != 0.) x->x_gain = g;
  81     return (x);
  82 }
  83
  84
  85 void equalizer_setup(void)
  86 {
  87     equ_class = class_new(gensym("equalizer"), (t_newmethod)equ_new, 0,
  88                                 sizeof(t_rbjfilter), 0,A_DEFFLOAT,A_DEFFLOAT,A_DEFFLOAT,0);
  89     class_addbang(equ_class,equ_bang);
  90     class_addfloat(equ_class,equ_float);
  91 }
  92
  93