usr.sbin/i4b/dtmfdecode/dtmfdecode.c

   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  * $Id: dtmfdecode.c,v 1.6 1999/12/13 21:25:24 hm Exp $
  10  *
  11  * $FreeBSD: src/usr.sbin/i4b/dtmfdecode/dtmfdecode.c,v 1.4.2.1 2001/08/01 17:45:02 obrien Exp $
  12  * $DragonFly: src/usr.sbin/i4b/dtmfdecode/dtmfdecode.c,v 1.3 2003/11/16 15:17:35 eirikn Exp $
  13  *
  14  * Extract DTMF signalling from ISDN4BSD A-law coded audio data
  15  *
  16  * A-Law to linear conversion from the sox package.
  17  *
  18  */
  19
  20 #include <stdio.h>
  21 #include <math.h>
  22
  23 /* Integer math scaling factor */
  24 #define FSC     (1<<12)
  25
  26 /* Alaw parameters */
  27 #define SIGN_BIT        (0x80)          /* Sign bit for a A-law byte. */
  28 #define QUANT_MASK      (0xf)           /* Quantization field mask. */
  29 #define SEG_SHIFT       (4)             /* Left shift for segment number. */
  30 #define SEG_MASK        (0x70)          /* Segment field mask. */
  31
  32 static int
  33 alaw2linear(unsigned char a_val)
  34 {
  35         int             t;
  36         int             seg;
  37
  38         a_val ^= 0x55;
  39
  40         t = (a_val & QUANT_MASK) << 4;
  41         seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
  42         switch (seg) {
  43         case 0:
  44                 t += 8;
  45                 break;
  46         case 1:
  47                 t += 0x108;
  48                 break;
  49         default:
  50                 t += 0x108;
  51                 t <<= seg - 1;
  52         }
  53         return ((a_val & SIGN_BIT) ? t : -t);
  54 }
  55
  56 #ifdef USE_COS
  57 /* The frequencies we're trying to detect */
  58 static int dtmf[8] = {697, 770, 852, 941, 1209, 1336, 1477, 1633};
  59 #else
  60 /* precalculated: p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC) */
  61 static int p1[8] = {-3497, -3369, -3212, -3027, -2384, -2040, -1635, -1164};
  62 #endif
  63
  64 /* This is the Q of the filter (pole radius) */
  65 #define POLRAD .99
  66
  67 #define P2 ((int)(POLRAD*POLRAD*FSC))
  68
  69 int
  70 main(int argc, char **argv)
  71 {
  72         int i, kk, t, nn, s, so, ia;
  73         int x, c, d, f, h[8], k[8], n, y[8];
  74 #ifdef USE_COS
  75         int p1[8];
  76 #endif
  77         int alaw[256];
  78         char key[256];
  79
  80         for (kk = 0; kk < 8; kk++) {
  81                 y[kk] = h[kk] = k[kk] = 0;
  82 #ifdef USE_COS
  83                 p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC);
  84 #endif
  85         }
  86
  87         for (i = 0; i < 256; i++) {
  88                 key[i] = '?';
  89                 alaw[i] = alaw2linear(i) / (32768/FSC);
  90         }
  91
  92         /* We encode the tones in 8 bits, translate those to symbol */
  93         key[0x00] = '\0';
  94
  95         key[0x11] = '1'; key[0x12] = '4'; key[0x14] = '7'; key[0x18] = '*';
  96         key[0x21] = '2'; key[0x22] = '5'; key[0x24] = '8'; key[0x28] = '0';
  97         key[0x41] = '3'; key[0x42] = '6'; key[0x44] = '9'; key[0x48] = '#';
  98         key[0x81] = 'A'; key[0x82] = 'B'; key[0x84] = 'C'; key[0x88] = 'D';
  99
 100         nn = 0;
 101         ia = 0;
 102         so = 0;
 103         t = 0;
 104         while ((i = getchar()) != EOF)
 105         {
 106                 t++;
 107
 108                 /* Convert to our format */
 109                 x = alaw[i];
 110
 111                 /* Input amplitude */
 112                 if (x > 0)
 113                         ia += (x - ia) / 128;
 114                 else
 115                         ia += (-x - ia) / 128;
 116
 117                 /* For each tone */
 118                 s = 0;
 119                 for(kk = 0; kk < 8; kk++) {
 120
 121                         /* Turn the crank */
 122                         c = (P2 * (x - k[kk])) / FSC;
 123                         d = x + c;
 124                         f = (p1[kk] * (d - h[kk])) / FSC;
 125                         n = x - k[kk] - c;
 126                         k[kk] = h[kk] + f;
 127                         h[kk] = f + d;
 128
 129                         /* Detect and Average */
 130                         if (n > 0)
 131                                 y[kk] += (n - y[kk]) / 64;
 132                         else
 133                                 y[kk] += (-n - y[kk]) / 64;
 134
 135                         /* Threshold */
 136                         if (y[kk] > FSC/10 && y[kk] > ia)
 137                                 s |= 1 << kk;
 138                 }
 139
 140                 /* Hysteresis and noise supressor */
 141                 if (s != so) {
 142 /* printf("x %d %x -> %x\n",t,so, s); */
 143                         nn = 0;
 144                         so = s;
 145                 } else if (nn++ == 520 && key[s]) {
 146                         putchar(key[s]);
 147 /* printf(" %d %x\n",t,s); */
 148                 }
 149         }
 150         putchar('\n');
 151         return (0);
 152 }