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/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you think
* this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
* ----------------------------------------------------------------------------
*
* $Id: dtmfdecode.c,v 1.5 1999/04/26 11:41:49 hm Exp $
*
* Extract DTMF signalling from ISDN4BSD A-law coded audio data
*
* A-Law to linear conversion from the sox package.
*
*/
#include <stdio.h>
#include <math.h>
/* Integer math scaling factor */
#define FSC (1<<12)
/* Alaw parameters */
#define SIGN_BIT (0x80) /* Sign bit for a A-law byte. */
#define QUANT_MASK (0xf) /* Quantization field mask. */
#define SEG_SHIFT (4) /* Left shift for segment number. */
#define SEG_MASK (0x70) /* Segment field mask. */
static int
alaw2linear(a_val)
unsigned char a_val;
{
int t;
int seg;
a_val ^= 0x55;
t = (a_val & QUANT_MASK) << 4;
seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
switch (seg) {
case 0:
t += 8;
break;
case 1:
t += 0x108;
break;
default:
t += 0x108;
t <<= seg - 1;
}
return ((a_val & SIGN_BIT) ? t : -t);
}
#ifdef USE_COS
/* The frequencies we're trying to detect */
static int dtmf[8] = {697, 770, 852, 941, 1209, 1336, 1477, 1633};
#else
/* precalculated: p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC) */
static int p1[8] = {-3497, -3369, -3212, -3027, -2384, -2040, -1635, -1164};
#endif
/* This is the Q of the filter (pole radius) */
#define POLRAD .99
#define P2 ((int)(POLRAD*POLRAD*FSC))
int
main(int argc, char **argv)
{
int i, kk, t, nn, s, so, ia;
int x, c, d, f, h[8], k[8], n, y[8];
#ifdef USE_COS
int p1[8];
#endif
int alaw[256];
char key[256];
for (kk = 0; kk < 8; kk++) {
y[kk] = h[kk] = k[kk] = 0;
#ifdef USE_COS
p1[kk] = (-cos(2 * 3.141592 * dtmf[kk] / 8000.0) * FSC);
#endif
}
for (i = 0; i < 256; i++) {
key[i] = '?';
alaw[i] = alaw2linear(i) / (32768/FSC);
}
/* We encode the tones in 8 bits, translate those to symbol */
key[0x00] = '\0';
key[0x11] = '1'; key[0x12] = '4'; key[0x14] = '7'; key[0x18] = '*';
key[0x21] = '2'; key[0x22] = '5'; key[0x24] = '8'; key[0x28] = '0';
key[0x41] = '3'; key[0x42] = '6'; key[0x44] = '9'; key[0x48] = '#';
key[0x81] = 'A'; key[0x82] = 'B'; key[0x84] = 'C'; key[0x88] = 'D';
nn = 0;
ia = 0;
so = 0;
t = 0;
while ((i = getchar()) != EOF)
{
t++;
/* Convert to our format */
x = alaw[i];
/* Input amplitude */
if (x > 0)
ia += (x - ia) / 128;
else
ia += (-x - ia) / 128;
/* For each tone */
s = 0;
for(kk = 0; kk < 8; kk++) {
/* Turn the crank */
c = (P2 * (x - k[kk])) / FSC;
d = x + c;
f = (p1[kk] * (d - h[kk])) / FSC;
n = x - k[kk] - c;
k[kk] = h[kk] + f;
h[kk] = f + d;
/* Detect and Average */
if (n > 0)
y[kk] += (n - y[kk]) / 64;
else
y[kk] += (-n - y[kk]) / 64;
/* Threshold */
if (y[kk] > FSC/10 && y[kk] > ia)
s |= 1 << kk;
}
/* Hysteresis and noise supressor */
if (s != so) {
/* printf("x %d %x -> %x\n",t,so, s); */
nn = 0;
so = s;
} else if (nn++ == 520 && key[s]) {
putchar(key[s]);
/* printf(" %d %x\n",t,s); */
}
}
putchar('\n');
return (0);
}
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