src/ptclib/dtmf.cxx

   1 /*
   2  * ----------------------------------------------------------------------------
   3  * "THE BEER-WARE LICENSE" (Revision 42):
   4  * <phk@FreeBSD.org> wrote this file.  As long as you retain this notice you
   5  * can do whatever you want with this stuff. If we meet some day, and you think
   6  * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
   7  * ----------------------------------------------------------------------------
   8  *
   9  * Extract DTMF signals from 16 bit PCM audio
  10  *
  11  * Originally written by Poul-Henning Kamp <phk@freebsd.org>
  12  * Made into a C++ class by Roger Hardiman <roger@freebsd.org>, January 2002
  13  *
  14  * $Log$
  15  * Revision 1.7  2003/03/17 07:39:25  robertj
  16  * Fixed possible invalid value causing DTMF detector to crash.
  17  *
  18  * Revision 1.6  2002/02/20 02:59:34  yurik
  19  * Added end of line to trace statement
  20  *
  21  * Revision 1.5  2002/02/12 10:21:56  rogerh
  22  * Stop sending '?' when a bad DTMF tone is detected.
  23  *
  24  * Revision 1.4  2002/01/24 11:14:45  rogerh
  25  * Back out robert's change. It did not work (no sign extending)
  26  * and replace it with a better solution which should be happy on both big
  27  * endian and little endian systems.
  28  *
  29  * Revision 1.3  2002/01/24 10:40:17  rogerh
  30  * Add version log
  31  *
  32  *
  33  */
  34
  35 #ifdef __GNUC__
  36 #pragma implementation "dtmf.h"
  37 #endif
  38
  39 #include <ptlib.h>
  40 #include <ptclib/dtmf.h>
  41
  42
  43 /* Integer math scaling factor */
  44 #define FSC     (1<<12)
  45
  46 /* This is the Q of the filter (pole radius) */
  47 #define POLRAD .99
  48
  49 #define P2 ((int)(POLRAD*POLRAD*FSC))
  50
  51
  52
  53 PDTMFDecoder::PDTMFDecoder()
  54 {
  55         // Initialise the class
  56         int i,kk;
  57         for (kk = 0; kk < 8; kk++) {
  58                 y[kk] = h[kk] = k[kk] = 0;
  59         }
  60
  61         nn = 0;
  62         ia = 0;
  63         so = 0;
  64
  65         for (i = 0; i < 256; i++) {
  66                 key[i] = '?';
  67         }
  68
  69         /* We encode the tones in 8 bits, translate those to symbol */
  70         key[0x11] = '1'; key[0x12] = '4'; key[0x14] = '7'; key[0x18] = '*';
  71         key[0x21] = '2'; key[0x22] = '5'; key[0x24] = '8'; key[0x28] = '0';
  72         key[0x41] = '3'; key[0x42] = '6'; key[0x44] = '9'; key[0x48] = '#';
  73         key[0x81] = 'A'; key[0x82] = 'B'; key[0x84] = 'C'; key[0x88] = 'D';
  74
  75         /* The frequencies we're trying to detect */
  76         /* These are precalculated to save processing power */
  77         /* static int dtmf[8] = {697, 770, 852, 941, 1209, 1336, 1477, 1633}; */
  78         /* p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC) */
  79         p1[0] = -3497; p1[1] = -3369; p1[2] = -3212; p1[3] = -3027;
  80         p1[4] = -2384; p1[5] = -2040; p1[6] = -1635; p1[7] = -1164;
  81 }
  82
  83
  84 PString PDTMFDecoder::Decode(const void *buf, PINDEX bytes)
  85 {
  86         int x;
  87         int s, kk;
  88         int c, d, f, n;
  89         short *buffer = (short *)buf;
  90
  91         PINDEX numSamples = bytes >> 1;
  92
  93         PString keyString;
  94
  95         PINDEX pos;
  96         for (pos = 0; pos < numSamples; pos++) {
  97
  98                 /* Read (and scale) the next 16 bit sample */
  99                 x = ((int)(*buffer++)) / (32768/FSC);
 100
 101                 /* Input amplitude */
 102                 if (x > 0)
 103                         ia += (x - ia) / 128;
 104                 else
 105                         ia += (-x - ia) / 128;
 106
 107                 /* For each tone */
 108                 s = 0;
 109                 for(kk = 0; kk < 8; kk++) {
 110
 111                         /* Turn the crank */
 112                         c = (P2 * (x - k[kk])) / FSC;
 113                         d = x + c;
 114                         f = (p1[kk] * (d - h[kk])) / FSC;
 115                         n = x - k[kk] - c;
 116                         k[kk] = h[kk] + f;
 117                         h[kk] = f + d;
 118
 119                         /* Detect and Average */
 120                         if (n > 0)
 121                                 y[kk] += (n - y[kk]) / 64;
 122                         else
 123                                 y[kk] += (-n - y[kk]) / 64;
 124
 125                         /* Threshold */
 126                         if (y[kk] > FSC/10 && y[kk] > ia)
 127                                 s |= 1 << kk;
 128                 }
 129
 130                 /* Hysteresis and noise supressor */
 131                 if (s != so) {
 132                         nn = 0;
 133                         so = s;
 134                 } else if (nn++ == 520 && s < 256 && key[s] != '?') {
 135                         PTRACE(3,"DTMF\tDetected '" << key[s] << "' in PCM-16 stream");
 136                         keyString += key[s];
 137                 }
 138         }
 139         return keyString;
 140 }