/* * ---------------------------------------------------------------------------- * "THE BEER-WARE LICENSE" (Revision 42): * 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 1.1.1.1 2001/01/06 13:00:36 martin Exp $ * * $FreeBSD$ * * Extract DTMF signalling from ISDN4BSD A-law coded audio data * * A-Law to linear conversion from the sox package. * */ #include #include /* 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(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); }