usr.sbin/isdn/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 1.3 2003/10/06 09:43:27 itojun Exp $
  10  *
  11  * $FreeBSD$
  12  *
  13  * Extract DTMF signalling from ISDN4BSD A-law coded audio data
  14  *
  15  * A-law to linear conversion from the sox package.
  16  *
  17  */
  18
  19 #include <stdio.h>
  20 #include <math.h>
  21
  22 /* Integer math scaling factor */
  23 #define FSC     (1<<12)
  24
  25 /* A-law parameters */
  26 #define SIGN_BIT        (0x80)          /* Sign bit for a A-law byte. */
  27 #define QUANT_MASK      (0xf)           /* Quantization field mask. */
  28 #define SEG_SHIFT       (4)             /* Left shift for segment number. */
  29 #define SEG_MASK        (0x70)          /* Segment field mask. */
  30
  31 static int alaw2linear(unsigned char a_val)
  32 {
  33         int             t;
  34         int             seg;
  35
  36         a_val ^= 0x55;
  37
  38         t = (a_val & QUANT_MASK) << 4;
  39         seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
  40         switch (seg) {
  41         case 0:
  42                 t += 8;
  43                 break;
  44         case 1:
  45                 t += 0x108;
  46                 break;
  47         default:
  48                 t += 0x108;
  49                 t <<= seg - 1;
  50         }
  51         return ((a_val & SIGN_BIT) ? t : -t);
  52 }
  53
  54 #ifdef USE_COS
  55 /* The frequencies we're trying to detect */
  56 static int dtmf[8] = {697, 770, 852, 941, 1209, 1336, 1477, 1633};
  57 #else
  58 /* precalculated: p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC) */
  59 static int p1[8] = {-3497, -3369, -3212, -3027, -2384, -2040, -1635, -1164};
  60 #endif
  61
  62 /* This is the Q of the filter (pole radius) */
  63 #define POLRAD .99
  64
  65 #define P2 ((int)(POLRAD*POLRAD*FSC))
  66
  67 int
  68 main(int argc, char **argv)
  69 {
  70         int i, kk, t, nn, s, so, ia;
  71         int x, c, d, f, h[8], k[8], n, y[8];
  72 #ifdef USE_COS
  73         int p1[8];
  74 #endif
  75         int alaw[256];
  76         char key[256];
  77
  78         for (kk = 0; kk < 8; kk++) {
  79                 y[kk] = h[kk] = k[kk] = 0;
  80 #ifdef USE_COS
  81                 p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC);
  82 #endif
  83         }
  84
  85         for (i = 0; i < 256; i++) {
  86                 key[i] = '?';
  87                 alaw[i] = alaw2linear(i) / (32768/FSC);
  88         }
  89
  90         /* We encode the tones in 8 bits, translate those to symbol */
  91         key[0x00] = '\0';
  92
  93         key[0x11] = '1'; key[0x12] = '4'; key[0x14] = '7'; key[0x18] = '*';
  94         key[0x21] = '2'; key[0x22] = '5'; key[0x24] = '8'; key[0x28] = '0';
  95         key[0x41] = '3'; key[0x42] = '6'; key[0x44] = '9'; key[0x48] = '#';
  96         key[0x81] = 'A'; key[0x82] = 'B'; key[0x84] = 'C'; key[0x88] = 'D';
  97
  98         nn = 0;
  99         ia = 0;
 100         so = 0;
 101         t = 0;
 102         while ((i = getchar()) != EOF)
 103         {
 104                 t++;
 105
 106                 /* Convert to our format */
 107                 x = alaw[i];
 108
 109                 /* Input amplitude */
 110                 if (x > 0)
 111                         ia += (x - ia) / 128;
 112                 else
 113                         ia += (-x - ia) / 128;
 114
 115                 /* For each tone */
 116                 s = 0;
 117                 for (kk = 0; kk < 8; kk++) {
 118
 119                         /* Turn the crank */
 120                         c = (P2 * (x - k[kk])) / FSC;
 121                         d = x + c;
 122                         f = (p1[kk] * (d - h[kk])) / FSC;
 123                         n = x - k[kk] - c;
 124                         k[kk] = h[kk] + f;
 125                         h[kk] = f + d;
 126
 127                         /* Detect and Average */
 128                         if (n > 0)
 129                                 y[kk] += (n - y[kk]) / 64;
 130                         else
 131                                 y[kk] += (-n - y[kk]) / 64;
 132
 133                         /* Threshold */
 134                         if (y[kk] > FSC/10 && y[kk] > ia)
 135                                 s |= 1 << kk;
 136                 }
 137
 138                 /* Hysteresis and noise supressor */
 139                 if (s != so) {
 140 /* printf("x %d %x -> %x\n",t,so, s); */
 141                         nn = 0;
 142                         so = s;
 143                 } else if (nn++ == 520 && key[s]) {
 144                         putchar(key[s]);
 145 /* printf(" %d %x\n",t,s); */
 146                 }
 147         }
 148         putchar('\n');
 149         return (0);
 150 }