X-Git-Url: http://git.eversberg.eu/gitweb.cgi?p=lcr.git;a=blobdiff_plain;f=ss5_decode.c;fp=ss5_decode.c;h=541f6beed9814fa588269fa8e56804378d65467c;hp=0000000000000000000000000000000000000000;hb=323cbc387b1a068f8e2bcfd1034666406ba18c93;hpb=96124cb106071709b490e7d055a212b12d3915fd

diff --git a/ss5_decode.c b/ss5_decode.c
new file mode 100644
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--- /dev/null
+++ b/ss5_decode.c
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+/*
+ * SS5 signal decoder.
+ *
+ * Copyright            by Andreas Eversberg (jolly@eversberg.eu)
+ *			based on different decoders such as ISDN4Linux
+ *			copyright by Karsten Keil
+ *
+ * This software may be used and distributed according to the terms
+ * of the GNU General Public License, incorporated herein by reference.
+ *
+ */
+
+#include "main.h"
+#include "ss5_decode.h"
+
+/* enable level debugging */
+//#define DEBUG_LEVELS
+
+#define NCOEFF		8	/* number of frequencies to be analyzed */
+
+#define MIN_DB		0.01995262 /* -17 db */
+#define DIFF_DB		0.31622777 /*  -5 db */
+#define SNR		1.3	/* noise may not exceed signal by that factor */
+
+/* For DTMF recognition:
+ * 2 * cos(2 * PI * k / N) precalculated for all k
+ */
+static signed long long cos2pik[NCOEFF] =
+{
+	/* k = 2*cos(2*PI*f/8000), k << 15 
+	 * 700, 900, 1100, 1300, 1500, 1700, 2400, 2600 */
+	55879, 49834, 42562, 34242, 25080, 15299, -20252, -29753
+};
+
+/* detection matrix for two frequencies */
+static char decode_two[8][8] =
+{
+	{' ', '1', '2', '4', '7', '*', ' ', ' '}, /* * = code 11 */
+	{'1', ' ', '3', '5', '8', '#', ' ', ' '}, /* # = code 12 */
+	{'2', '3', ' ', '6', '9', 'a', ' ', ' '}, /* a = KP1 */
+	{'4', '5', '6', ' ', '0', 'b', ' ', ' '}, /* b = KP2 */
+	{'7', '8', '9', '0', ' ', 'c', ' ', ' '}, /* c = ST */
+	{'*', '#', 'a', 'b', 'c', ' ', ' ', ' '},
+	{' ', ' ', ' ', ' ', ' ', ' ', ' ', 'C'}, /* C = 2600+2400 */
+	{' ', ' ', ' ', ' ', ' ', ' ', 'C', ' '}
+};
+
+static char decode_one[8] =
+	{' ', ' ', ' ', ' ', ' ', ' ', 'A', 'B'}; /* A = 2400, B = 2600 */
+/*
+ * calculate the coefficients of the given sample and decode
+ */
+
+char ss5_decode(unsigned char *data, int len)
+{
+	signed short buf[len];
+	signed long sk, sk1, sk2, low, high;
+	int k, n, i;
+	int f1 = 0, f2 = 0, f3 = 0;
+	double result[NCOEFF], power, noise, snr;
+	signed long long cos2pik_;
+	char digit = ' ';
+
+	/* convert samples */
+	for (i = 0; i < len; i++)
+		buf[i] = audio_law_to_s32[*data++];
+
+	/* now we have a full buffer of signed long samples - we do goertzel */
+	for (k = 0; k < NCOEFF; k++) {
+		sk = 0;
+		sk1 = 0;
+		sk2 = 0;
+		cos2pik_ = cos2pik[k];
+		for (n = 0; n < len; n++) {
+			sk = ((cos2pik_*sk1)>>15) - sk2 + buf[n];
+			sk2 = sk1;
+			sk1 = sk;
+		}
+		sk >>= 8;
+		sk2 >>= 8;
+		if (sk > 32767 || sk < -32767 || sk2 > 32767 || sk2 < -32767)
+			PERROR("Tone-Detection overflow\n");
+		/* compute |X(k)|**2 */
+		result[k] = sqrt (
+				(sk * sk) -
+				(((cos2pik[k] * sk) >> 15) * sk2) +
+				(sk2 * sk2)
+			) / len / 62; /* level of 1 is 0 db*/
+	}
+
+	/* now we do noise level calculation */
+	low = 32767;
+	high = -32768;
+	for (n = 0; n < len; n++) {
+		sk = buf[n];
+		if (sk < low)
+			low = sk;
+		if (sk > high)
+			high = sk;
+	}
+	noise = ((double)(high-low) / 65536.0);
+
+	/* find the two loudest frequencies + one less lower frequency to detect noise */
+	power = 0.0;
+	for (i = 0; i < NCOEFF; i++) {
+		if (result[i] > power) {
+			power = result[i];
+			f1 = i;
+		}
+	}
+	power = 0.0;
+	for (i = 0; i < NCOEFF; i++) {
+		if (i != f1 && result[i] > power) {
+			power = result[i];
+			f2 = i;
+		}
+	}
+	power = 0.0;
+	for (i = 0; i < NCOEFF; i++) {
+		if (i != f1  && i != f2 && result[i] > power) {
+			power = result[i];
+			f3 = i;
+		}
+	}
+
+#if 0
+	/* check one frequency */
+	if (result[f1] > MIN_DB /* must be at least -17 db */
+	 && result[f1]*DIFF_DB > result[f2]) /* must be 5 db above other tones */
+		digit = decode_one[f1];
+	/* check two frequencies */
+	if (result[f1] > MIN_DB && result[f2] > MIN_DB /* must be at lease -17 db */
+	 && result[f1]*DIFF_DB <= result[f2] /* f2 must be not less than 5 db below f1 */
+	 && result[f1]*DIFF_DB > result[f3]) /* f1 must be 5 db above other tones */
+		digit = decode_two[f1][f2];
+#endif
+	snr = 0;
+	/* check one frequency */
+	if (result[f1] > MIN_DB /* must be at least -17 db */
+	 && result[f1]*SNR > noise) { /*  */
+		digit = decode_one[f1];
+		snr = result[f1] / noise;
+	}
+	/* check two frequencies */
+	if (result[f1] > MIN_DB && result[f2] > MIN_DB /* must be at lease -17 db */
+	 && result[f1]*DIFF_DB <= result[f2] /* f2 must be not less than 5 db below f1 */
+	 && (result[f1]+result[f2])*SNR > noise) { /* */
+		digit = decode_two[f1][f2];
+		snr = (result[f1]+result[f2]) / noise;
+	}
+
+	/* debug powers */
+#ifdef DEBUG_LEVELS
+	for (i = 0; i < NCOEFF; i++)
+		printf("%d:%3d %c ", i, (int)(result[i]*100), (f1==i || f2==i)?'*':' ');
+	printf("N:%3d digit:%c snr=%3d\n", (int)(noise*100), digit, (int)(snr*100));
+#endif
+
+	return digit;
+}
+
+void ss5_test_decode(void)
+{
+#ifdef DEBUG_LEVELS
+	double phase;
+	int i, j;
+	signed short sample;
+
+	unsigned char buffer[SS5_DECODER_NPOINTS];
+	for (i = 0; i < 4000; i += 10) {
+		phase = 2.0 * 3.14159265 * i / 8000.0;
+		for (j = 0; j < SS5_DECODER_NPOINTS; j++) {
+			sample = sin(phase * j) * 1000;
+			buffer[j] = audio_s16_to_law[sample & 0xffff];
+		}
+		printf("FRQ:%04d:", i);
+		ss5_decode(buffer, SS5_DECODER_NPOINTS);
+	}
+#endif
+}
+