src/compandt.h

   1 /* libSoX Compander Transfer Function  (c) 2007 robs@users.sourceforge.net
   2  *
   3  * This library is free software; you can redistribute it and/or modify it
   4  * under the terms of the GNU Lesser General Public License as published by
   5  * the Free Software Foundation; either version 2.1 of the License, or (at
   6  * your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this library; if not, write to the Free Software Foundation,
  15  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  16  */
  17
  18 #include <math.h>
  19
  20 typedef struct {
  21   struct sox_compandt_segment {
  22     double x, y;              /* 1st point in segment */
  23     double a, b;              /* Quadratic coeffecients for rest of segment */
  24   } * segments;
  25   double in_min_lin;
  26   double out_min_lin;
  27   double outgain_dB;        /* Post processor gain */
  28   double curve_dB;
  29 } sox_compandt_t;
  30
  31 sox_bool lsx_compandt_parse(sox_compandt_t * t, char * points, char * gain);
  32 sox_bool lsx_compandt_show(sox_compandt_t * t, sox_plot_t plot);
  33 void    lsx_compandt_kill(sox_compandt_t * p);
  34
  35 /* Place in header to allow in-lining */
  36 static double lsx_compandt(sox_compandt_t * t, double in_lin)
  37 {
  38   struct sox_compandt_segment * s;
  39   double in_log, out_log;
  40
  41   if (in_lin <= t->in_min_lin)
  42     return t->out_min_lin;
  43
  44   in_log = log(in_lin);
  45
  46   for (s = t->segments + 1; in_log > s[1].x; ++s);
  47
  48   in_log -= s->x;
  49   out_log = s->y + in_log * (s->a * in_log + s->b);
  50
  51   return exp(out_log);
  52 }