apps/plugins/pdbox/PDa/extra/filters.h

   1 /*
   2
   3  These filter coefficients computations are taken from
   4  http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt
   5
   6  written by Robert Bristow-Johnson
   7
   8 */
   9
  10
  11 #ifndef __GGEE_FILTERS_H__
  12 #define __GGEE_FILTERS_H__
  13
  14
  15
  16 #ifndef M_PI
  17 #define M_PI 3.141593f
  18 #endif
  19
  20
  21 #include <math.h>
  22 #define LN2 0.69314718
  23 #define e_A(g) (pow(10,(g/40.)))
  24 #define e_omega(f,r) (2.0*M_PI*f/r)
  25 #define e_alpha(bw,omega) (sin(omega)*sinh(LN2/2. * bw * omega/sin(omega)))
  26 #define e_beta(a,S) (sqrt((a*a + 1)/(S) - (a-1)*(a-1)))
  27
  28
  29
  30
  31 typedef struct _rbjfilter
  32 {
  33      t_object x_obj;
  34      t_float  x_rate;
  35      t_float  x_freq;
  36      t_float  x_gain;
  37      t_float  x_bw;
  38 } t_rbjfilter;
  39
  40
  41 static int check_stability(t_float fb1,
  42                             t_float fb2,
  43                             t_float ff1,
  44                             t_float ff2,
  45                             t_float ff3)
  46 {
  47     float discriminant = fb1 * fb1 + 4 * fb2;
  48
  49     if (discriminant < 0) /* imaginary roots -- resonant filter */
  50     {
  51             /* they're conjugates so we just check that the product
  52             is less than one */
  53         if (fb2 >= -1.0f) goto stable;
  54     }
  55     else    /* real roots */
  56     {
  57             /* check that the parabola 1 - fb1 x - fb2 x^2 has a
  58                 vertex between -1 and 1, and that it's nonnegative
  59                 at both ends, which implies both roots are in [1-,1]. */
  60         if (fb1 <= 2.0f && fb1 >= -2.0f &&
  61             1.0f - fb1 -fb2 >= 0 && 1.0f + fb1 - fb2 >= 0)
  62                 goto stable;
  63     }
  64     return 0;
  65 stable:
  66     return 1;
  67 }
  68
  69
  70
  71
  72
  73
  74 #endif
  75 /*
  76
  77  These filter coefficients computations are taken from
  78  http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt
  79
  80  written by Robert Bristow-Johnson
  81
  82 */
  83
  84
  85 #ifndef __GGEE_FILTERS_H__
  86 #define __GGEE_FILTERS_H__
  87
  88
  89
  90 #ifndef M_PI
  91 #define M_PI 3.141593f
  92 #endif
  93
  94
  95 #include <math.h>
  96 #define LN2 0.69314718
  97 #define e_A(g) (pow(10,(g/40.)))
  98 #define e_omega(f,r) (2.0*M_PI*f/r)
  99 #define e_alpha(bw,omega) (sin(omega)*sinh(LN2/2. * bw * omega/sin(omega)))
 100 #define e_beta(a,S) (sqrt((a*a + 1)/(S) - (a-1)*(a-1)))
 101
 102
 103
 104
 105 typedef struct _rbjfilter
 106 {
 107      t_object x_obj;
 108      t_float  x_rate;
 109      t_float  x_freq;
 110      t_float  x_gain;
 111      t_float  x_bw;
 112 } t_rbjfilter;
 113
 114
 115 static int check_stability(t_float fb1,
 116                             t_float fb2,
 117                             t_float ff1,
 118                             t_float ff2,
 119                             t_float ff3)
 120 {
 121     float discriminant = fb1 * fb1 + 4 * fb2;
 122
 123     if (discriminant < 0) /* imaginary roots -- resonant filter */
 124     {
 125             /* they're conjugates so we just check that the product
 126             is less than one */
 127         if (fb2 >= -1.0f) goto stable;
 128     }
 129     else    /* real roots */
 130     {
 131             /* check that the parabola 1 - fb1 x - fb2 x^2 has a
 132                 vertex between -1 and 1, and that it's nonnegative
 133                 at both ends, which implies both roots are in [1-,1]. */
 134         if (fb1 <= 2.0f && fb1 >= -2.0f &&
 135             1.0f - fb1 -fb2 >= 0 && 1.0f + fb1 - fb2 >= 0)
 136                 goto stable;
 137     }
 138     return 0;
 139 stable:
 140     return 1;
 141 }
 142
 143
 144
 145
 146
 147
 148 #endif