4 * Copyright by Andreas Eversberg (jolly@eversberg.eu)
5 * based on different decoders such as ISDN4Linux
6 * copyright by Karsten Keil
8 * This software may be used and distributed according to the terms
9 * of the GNU General Public License, incorporated herein by reference.
14 #include "ss5_decode.h"
16 /* enable level debugging */
17 //#define DEBUG_LEVELS
19 #define NCOEFF 8 /* number of frequencies to be analyzed */
21 #define TONE_MIN_DB 0.01995262 /* -17 db */
22 #define TONE_DIFF_DB 0.2 // 0.31622777 /* -5 db */
23 #define NOISE_MIN_DB (TONE_MIN_DB / 2) /* noise must be higher than the minimum of two tones */
24 #define SNR 1.3 /* noise may not exceed signal by that factor */
26 /* For DTMF recognition:
27 * 2 * cos(2 * PI * k / N) precalculated for all k
29 static signed long long cos2pik[NCOEFF] =
31 /* k = 2*cos(2*PI*f/8000), k << 15
32 * 700, 900, 1100, 1300, 1500, 1700, 2400, 2600 */
33 55879, 49834, 42562, 34242, 25080, 15299, -20252, -29753
36 /* detection matrix for two frequencies */
37 static char decode_two[8][8] =
39 {' ', '1', '2', '4', '7', '*', ' ', ' '}, /* * = code 11 */
40 {'1', ' ', '3', '5', '8', '#', ' ', ' '}, /* # = code 12 */
41 {'2', '3', ' ', '6', '9', 'a', ' ', ' '}, /* a = KP1 */
42 {'4', '5', '6', ' ', '0', 'b', ' ', ' '}, /* b = KP2 */
43 {'7', '8', '9', '0', ' ', 'c', ' ', ' '}, /* c = ST */
44 {'*', '#', 'a', 'b', 'c', ' ', ' ', ' '},
45 {' ', ' ', ' ', ' ', ' ', ' ', ' ', 'C'}, /* C = 2600+2400 */
46 {' ', ' ', ' ', ' ', ' ', ' ', 'C', ' '}
49 static char decode_one[8] =
50 {' ', ' ', ' ', ' ', ' ', ' ', 'A', 'B'}; /* A = 2400, B = 2600 */
52 * calculate the coefficients of the given sample and decode
55 char ss5_decode(unsigned char *data, int len, double *_quality)
57 signed short buf[len];
58 signed long sk, sk1, sk2, low, high;
61 double result[NCOEFF], power, noise;
62 signed long long cos2pik_;
67 for (i = 0; i < len; i++)
68 buf[i] = audio_law_to_s32[*data++];
70 /* now we do noise level calculation */
73 for (n = 0; n < len; n++) {
80 noise = ((double)(high-low) / 65536.0);
82 /* check for minimum noise, or tone detection will not be necessary */
83 if (noise < NOISE_MIN_DB)
86 /* now we have a full buffer of signed long samples - we do goertzel */
87 for (k = 0; k < NCOEFF; k++) {
91 cos2pik_ = cos2pik[k];
92 for (n = 0; n < len; n++) {
93 sk = ((cos2pik_*sk1)>>15) - sk2 + buf[n];
99 if (sk > 32767 || sk < -32767 || sk2 > 32767 || sk2 < -32767)
100 PERROR("Tone-Detection overflow\n");
101 /* compute |X(k)|**2 */
104 (((cos2pik[k] * sk) >> 15) * sk2) +
106 ) / len / 62; /* level of 1 is 0 db*/
109 /* find the two loudest frequencies + one less lower frequency to detect noise */
111 for (i = 0; i < NCOEFF; i++) {
112 if (result[i] > power) {
118 for (i = 0; i < NCOEFF; i++) {
119 if (i != f1 && result[i] > power) {
126 /* check one frequency */
127 if (result[f1] > TONE_MIN_DB /* must be at least -17 db */
128 && result[f1]*SNR > noise) { /* */
129 digit = decode_one[f1];
131 quality = result[f1] / noise;
133 /* check two frequencies */
134 if (result[f1] > TONE_MIN_DB && result[f2] > TONE_MIN_DB /* must be at lease -17 db */
135 && result[f1]*TONE_DIFF_DB <= result[f2] /* f2 must be not less than 5 db below f1 */
136 && (result[f1]+result[f2])*SNR > noise) { /* */
137 digit = decode_two[f1][f2];
139 quality = (result[f1]+result[f2]) / noise;
144 for (i = 0; i < NCOEFF; i++)
145 printf("%d:%3d %c ", i, (int)(result[i]*100), (f1==i || f2==i)?'*':' ');
146 printf("N:%3d digit:%c quality=%3d%%\n", (int)(noise*100), digit, (int)(quality*100));
147 // if (result[f1]*TONE_DIFF_DB <= result[f2]) /* f2 must be not less than 5 db below f1 */
156 void ss5_test_decode(void)
163 unsigned char buffer[SS5_DECODER_NPOINTS];
164 for (i = 0; i < 4000; i += 10) {
165 phase = 2.0 * 3.14159265 * i / 8000.0;
166 for (j = 0; j < SS5_DECODER_NPOINTS; j++) {
167 sample = sin(phase * j) * 1000;
168 buffer[j] = audio_s16_to_law[sample & 0xffff];
170 printf("FRQ:%04d:", i);
171 ss5_decode(buffer, SS5_DECODER_NPOINTS);