153 lines
3.6 KiB
C
153 lines
3.6 KiB
C
/*
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* ----------------------------------------------------------------------------
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* "THE BEER-WARE LICENSE" (Revision 42):
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* <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
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* can do whatever you want with this stuff. If we meet some day, and you think
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* this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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* ----------------------------------------------------------------------------
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*
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* $Id: dtmfdecode.c,v 1.6 1999/12/13 21:25:24 hm Exp $
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*
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* $FreeBSD$
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*
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* Extract DTMF signalling from ISDN4BSD A-law coded audio data
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*
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* A-Law to linear conversion from the sox package.
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*
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*/
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#include <stdio.h>
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#include <math.h>
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/* Integer math scaling factor */
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#define FSC (1<<12)
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/* Alaw parameters */
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#define SIGN_BIT (0x80) /* Sign bit for an A-law byte. */
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#define QUANT_MASK (0xf) /* Quantization field mask. */
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#define SEG_SHIFT (4) /* Left shift for segment number. */
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#define SEG_MASK (0x70) /* Segment field mask. */
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static int
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alaw2linear(a_val)
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unsigned char a_val;
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{
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int t;
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int seg;
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a_val ^= 0x55;
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t = (a_val & QUANT_MASK) << 4;
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seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
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switch (seg) {
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case 0:
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t += 8;
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break;
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case 1:
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t += 0x108;
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break;
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default:
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t += 0x108;
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t <<= seg - 1;
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}
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return ((a_val & SIGN_BIT) ? t : -t);
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}
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#ifdef USE_COS
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/* The frequencies we're trying to detect */
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static int dtmf[8] = {697, 770, 852, 941, 1209, 1336, 1477, 1633};
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#else
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/* precalculated: p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC) */
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static int p1[8] = {-3497, -3369, -3212, -3027, -2384, -2040, -1635, -1164};
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#endif
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/* This is the Q of the filter (pole radius) */
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#define POLRAD .99
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#define P2 ((int)(POLRAD*POLRAD*FSC))
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int
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main(int argc, char **argv)
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{
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int i, kk, t, nn, s, so, ia;
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int x, c, d, f, h[8], k[8], n, y[8];
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#ifdef USE_COS
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int p1[8];
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#endif
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int alaw[256];
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char key[256];
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for (kk = 0; kk < 8; kk++) {
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y[kk] = h[kk] = k[kk] = 0;
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#ifdef USE_COS
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p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC);
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#endif
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}
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for (i = 0; i < 256; i++) {
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key[i] = '?';
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alaw[i] = alaw2linear(i) / (32768/FSC);
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}
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/* We encode the tones in 8 bits, translate those to symbol */
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key[0x00] = '\0';
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key[0x11] = '1'; key[0x12] = '4'; key[0x14] = '7'; key[0x18] = '*';
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key[0x21] = '2'; key[0x22] = '5'; key[0x24] = '8'; key[0x28] = '0';
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key[0x41] = '3'; key[0x42] = '6'; key[0x44] = '9'; key[0x48] = '#';
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key[0x81] = 'A'; key[0x82] = 'B'; key[0x84] = 'C'; key[0x88] = 'D';
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nn = 0;
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ia = 0;
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so = 0;
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t = 0;
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while ((i = getchar()) != EOF)
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{
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t++;
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/* Convert to our format */
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x = alaw[i];
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/* Input amplitude */
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if (x > 0)
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ia += (x - ia) / 128;
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else
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ia += (-x - ia) / 128;
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/* For each tone */
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s = 0;
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for(kk = 0; kk < 8; kk++) {
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/* Turn the crank */
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c = (P2 * (x - k[kk])) / FSC;
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d = x + c;
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f = (p1[kk] * (d - h[kk])) / FSC;
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n = x - k[kk] - c;
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k[kk] = h[kk] + f;
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h[kk] = f + d;
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/* Detect and Average */
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if (n > 0)
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y[kk] += (n - y[kk]) / 64;
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else
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y[kk] += (-n - y[kk]) / 64;
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/* Threshold */
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if (y[kk] > FSC/10 && y[kk] > ia)
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s |= 1 << kk;
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}
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/* Hysteresis and noise supressor */
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if (s != so) {
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/* printf("x %d %x -> %x\n",t,so, s); */
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nn = 0;
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so = s;
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} else if (nn++ == 520 && key[s]) {
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putchar(key[s]);
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/* printf(" %d %x\n",t,s); */
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}
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}
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putchar('\n');
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return (0);
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}
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