apps/plugins/pdbox/PDa/extra/lowshelf.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 /* ------------------- lowshelf ----------------------------*/
  31
  32 static t_class *lowshelf_class;
  33
  34 void lowshelf_bang(t_rbjfilter *x)
  35 {
  36      t_atom at[5];
  37      t_float omega = e_omega(x->x_freq,x->x_rate);
  38      t_float A = e_A(x->x_gain);
  39      t_float cs = cos(omega);
  40      t_float sn = sin(omega);
  41      t_float beta = e_beta(A,x->x_bw*0.01);
  42
  43      t_float b0 =    A*((A+1) - (A-1)*cs + beta*sn);
  44      t_float b1 = 2.*A*((A-1) - (A+1)*cs);
  45      t_float b2 =    A*((A+1) - (A-1)*cs - beta*sn);
  46      t_float a0 =      ((A+1) + (A-1)*cs + beta*sn);
  47      t_float a1 =  -2.*((A-1) + (A+1)*cs);
  48      t_float a2 =      ((A+1) + (A-1)*cs - beta*sn);
  49
  50 /*     post("bang %f %f %f",x->x_freq, x->x_gain, x->x_bw); */
  51
  52      if (!check_stability(-a1/a0,-a2/a0,b0/a0,b1/a0,b2/a0)) {
  53        post("lowshelf: filter unstable -> resetting");
  54        a0=1.;a1=0.;a2=0.;
  55        b0=1.;b1=0.;b2=0.;
  56      }
  57
  58      SETFLOAT(at,-a1/a0);
  59      SETFLOAT(at+1,-a2/a0);
  60      SETFLOAT(at+2,b0/a0);
  61      SETFLOAT(at+3,b1/a0);
  62      SETFLOAT(at+4,b2/a0);
  63
  64      outlet_list(x->x_obj.ob_outlet,&s_list,5,at);
  65 }
  66
  67
  68 void lowshelf_float(t_rbjfilter *x,t_floatarg f)
  69 {
  70      x->x_freq = f;
  71      lowshelf_bang(x);
  72 }
  73
  74
  75 static void *lowshelf_new(t_floatarg f,t_floatarg g,t_floatarg bw)
  76 {
  77     t_rbjfilter *x = (t_rbjfilter *)pd_new(lowshelf_class);
  78
  79     x->x_rate = 44100.0;
  80     outlet_new(&x->x_obj,&s_float);
  81     floatinlet_new(&x->x_obj, &x->x_gain);
  82     floatinlet_new(&x->x_obj, &x->x_bw);
  83     if (f > 0.) x->x_freq = f;
  84     if (bw > 0.) x->x_bw = bw;
  85     if (g != 0.) x->x_gain = g;
  86     return (x);
  87 }
  88
  89
  90 void lowshelf_setup(void)
  91 {
  92     lowshelf_class = class_new(gensym("lowshelf"), (t_newmethod)lowshelf_new, 0,
  93                                 sizeof(t_rbjfilter), 0,A_DEFFLOAT,A_DEFFLOAT,A_DEFFLOAT,0);
  94     class_addbang(lowshelf_class,lowshelf_bang);
  95     class_addfloat(lowshelf_class,lowshelf_float);
  96 }
  97
  98