Add DTMF decoder to libdtmf

Note: This decoder has no user yet.
5 years ago · 9e75e64787
parent 44247ffb53
commit 9e75e64787
6 changed files with 421 additions and 1 deletions
--- a/.gitignore
+++ b/.gitignore
@ -61,6 +61,7 @@ src/test/test_filter
 src/test/test_sendevolumenregler
 src/test/test_compandor
 src/test/test_emphasis
+src/test/test_dtmf
 src/test/test_dms
 src/test/test_sms
 src/test/test_performance
--- a/src/libdtmf/Makefile.am
+++ b/src/libdtmf/Makefile.am
@ -3,4 +3,5 @@ AM_CPPFLAGS = -Wall -Wextra -g $(all_includes)
 noinst_LIBRARIES = libdtmf.a

 libdtmf_a_SOURCES = \
-	dtmf_encode.c
+	dtmf_encode.c \
+	dtmf_decode.c
--- a/src/libdtmf/dtmf_decode.c
+++ b/src/libdtmf/dtmf_decode.c
@ -0,0 +1,259 @@
+/* DTMF coder
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <math.h>
+#include "../libsample/sample.h"
+#include "dtmf_decode.h"
+
+//#define DEBUG
+
+#define level2db(level)	(20 * log10(level))
+#define db2level(db)	pow(10, (double)db / 20.0)
+
+#define DTMF_LOW_1	697.0
+#define DTMF_LOW_2	770.0
+#define DTMF_LOW_3	852.0
+#define DTMF_LOW_4	941.0
+#define DTMF_HIGH_1	1209.0
+#define DTMF_HIGH_2	1336.0
+#define DTMF_HIGH_3	1477.0
+#define DTMF_HIGH_4	1633.0
+
+static const char dtmf_digit[] = "     123A456B789C*0#D";
+
+#ifdef DEBUG
+const char *_debug_amplitude(double level)
+{
+        static char text[42];
+
+	strcpy(text, "                    :                    ");
+	if (level > 1.0)
+		level = 1.0;
+	if (level < -1.0)
+		level = -1.0;
+	text[20 + (int)(level * 20)] = '*';
+
+	return text;
+}
+#endif
+
+int dtmf_decode_init(dtmf_dec_t *dtmf, void *priv, void (*recv_digit)(void *priv, char digit, dtmf_meas_t *meas), int samplerate, double max_amplitude, double min_amplitude)
+{
+	int rc;
+
+	memset(dtmf, 0, sizeof(*dtmf));
+	dtmf->priv = priv;
+	dtmf->recv_digit = recv_digit;
+	dtmf->samplerate = samplerate;
+	dtmf->freq_tollerance = 3.0;
+	dtmf->max_amplitude = max_amplitude;
+	dtmf->min_amplitude = min_amplitude;
+	dtmf->forward_twist = db2level(4.0);
+	dtmf->reverse_twist = db2level(8.0);
+	dtmf->time_detect = (int)(0.025 * (double)samplerate);
+	dtmf->time_meas = (int)(0.015 * (double)samplerate);
+	dtmf->time_pause = (int)(0.010 * (double)samplerate);
+
+	/* init fm demodulator */
+	rc = fm_demod_init(&dtmf->demod_low, (double)samplerate, (DTMF_LOW_1 + DTMF_LOW_4) / 2.0, DTMF_LOW_4 - DTMF_LOW_1);
+	if (rc < 0)
+		goto error;
+	rc = fm_demod_init(&dtmf->demod_high, (double)samplerate, (DTMF_HIGH_1 + DTMF_HIGH_4) / 2.0, DTMF_HIGH_4 - DTMF_HIGH_1);
+	if (rc < 0)
+		goto error;
+
+	/* use fourth order (2 iter) filter, since it is as fast as second order (1 iter) filter */
+	iir_lowpass_init(&dtmf->freq_lp[0], 100.0, samplerate, 2);
+	iir_lowpass_init(&dtmf->freq_lp[1], 100.0, samplerate, 2);
+
+	return 0;
+
+error:
+	dtmf_decode_exit(dtmf);
+	return rc;
+}
+
+void dtmf_decode_exit(dtmf_dec_t *dtmf)
+{
+	fm_demod_exit(&dtmf->demod_low);
+	fm_demod_exit(&dtmf->demod_high);
+}
+
+void dtmf_decode_filter(dtmf_dec_t *dtmf, sample_t *samples, int length, sample_t *frequency_low, sample_t *frequency_high, sample_t *amplitude_low, sample_t *amplitude_high)
+{
+	sample_t I_low[length], Q_low[length];
+	sample_t I_high[length], Q_high[length];
+	int i;
+
+	fm_demodulate_real(&dtmf->demod_low, frequency_low, length, samples, I_low, Q_low);
+	fm_demodulate_real(&dtmf->demod_high, frequency_high, length, samples, I_high, Q_high);
+	/* peak amplitude is the length of I/Q vector
+	 * since we filter out the unwanted modulation product, the vector is only half of length */
+	for (i = 0; i < length; i++) {
+		amplitude_low[i] = sqrt(I_low[i] * I_low[i] + Q_low[i] * Q_low[i]) * 2.0;
+		amplitude_high[i] = sqrt(I_high[i] * I_high[i] + Q_high[i] * Q_high[i]) * 2.0;
+	}
+	iir_process(&dtmf->freq_lp[0], frequency_low, length);
+	iir_process(&dtmf->freq_lp[1], frequency_high, length);
+}
+void dtmf_decode(dtmf_dec_t *dtmf, sample_t *samples, int length)
+{
+	sample_t frequency_low[length], amplitude_low[length];
+	sample_t frequency_high[length], amplitude_high[length];
+	double tollerance, min_amplitude, max_amplitude, forward_twist, reverse_twist, f1, f2;
+	int time_detect, time_meas, time_pause;
+	int low = 0, high = 0;
+	char detected, digit;
+	int count;
+	int aplitude_ok, twist_ok;
+	int i;
+
+	tollerance = dtmf->freq_tollerance;
+	min_amplitude = dtmf->min_amplitude;
+	max_amplitude = dtmf->max_amplitude;
+	forward_twist = dtmf->forward_twist;
+	reverse_twist = dtmf->reverse_twist;
+	time_detect = dtmf->time_detect;
+	time_meas = dtmf->time_meas;
+	time_pause = dtmf->time_pause;
+	detected = dtmf->detected;
+	count = dtmf->count;
+
+	/* FM/AM demod */
+	dtmf_decode_filter(dtmf, samples, length, frequency_low, frequency_high, amplitude_low, amplitude_high);
+
+	for (i = 0; i < length; i++) {
+#ifdef DEBUG
+		printf("%s %.5f\n", _debug_amplitude(samples[i]/2.0), samples[i]/2.0);
+#endif
+		/* get frequency of low frequencies, correct amplitude drop at cutoff point */
+		f1 = frequency_low[i] + (DTMF_LOW_1 + DTMF_LOW_4) / 2.0;
+		if (f1 >= DTMF_LOW_1 - tollerance && f1 <= DTMF_LOW_1 + tollerance) {
+			/* cutoff point */
+			amplitude_low[i] /= 0.7071;
+			low = 1;
+			f1 -= DTMF_LOW_1;
+		} else
+		if (f1 >= DTMF_LOW_2 - tollerance && f1 <= DTMF_LOW_2 + tollerance) {
+			amplitude_low[i] /= 1.0734;
+			low = 2;
+			f1 -= DTMF_LOW_2;
+		} else
+		if (f1 >= DTMF_LOW_3 - tollerance && f1 <= DTMF_LOW_3 + tollerance) {
+			amplitude_low[i] /= 1.0389;
+			low = 3;
+			f1 -= DTMF_LOW_3;
+		} else
+		if (f1 >= DTMF_LOW_4 - tollerance && f1 <= DTMF_LOW_4 + tollerance) {
+			/* cutoff point */
+			amplitude_low[i] /= 0.7071;
+			low = 4;
+			f1 -= DTMF_LOW_4;
+		} else
+			low = 0;
+		/* get frequency of high frequencies, correct amplitude drop at cutoff point */
+		f2 = frequency_high[i] + (DTMF_HIGH_1 + DTMF_HIGH_4) / 2.0;
+		if (f2 >= DTMF_HIGH_1 - tollerance && f2 <= DTMF_HIGH_1 + tollerance) {
+			/* cutoff point */
+			amplitude_high[i] /= 0.7071;
+			high = 1;
+			f2 -= DTMF_HIGH_1;
+		} else
+		if (f2 >= DTMF_HIGH_2 - tollerance && f2 <= DTMF_HIGH_2 + tollerance) {
+			amplitude_high[i] /= 1.0731;
+			high = 2;
+			f2 -= DTMF_HIGH_2;
+		} else
+		if (f2 >= DTMF_HIGH_3 - tollerance && f2 <= DTMF_HIGH_3 + tollerance) {
+			amplitude_high[i] /= 1.0372;
+			high = 3;
+			f2 -= DTMF_HIGH_3;
+		} else
+		if (f2 >= DTMF_HIGH_4 - tollerance && f2 <= DTMF_HIGH_4 + tollerance) {
+			/* cutoff point */
+			amplitude_high[i] /= 0.7071;
+			high = 4;
+			f2 -= DTMF_HIGH_4;
+		} else
+			high = 0;
+		digit = 0;
+		aplitude_ok = 0;
+		twist_ok = 0;
+		if (low && high) {
+			digit = dtmf_digit[low*4+high];
+			/* check for limits */
+			if (amplitude_low[i] <= max_amplitude && amplitude_low[i] >= min_amplitude && amplitude_high[i] <= max_amplitude && amplitude_high[i] >= min_amplitude) {
+				aplitude_ok = 1;
+#ifdef DEBUG
+				printf("%.5f %.5f %.1f\n", amplitude_low[i], amplitude_high[i], level2db(amplitude_high[i] / amplitude_low[i]));
+#endif
+				if (amplitude_high[i] / amplitude_low[i] <= forward_twist && amplitude_low[i] / amplitude_high[i] <= reverse_twist)
+					twist_ok = 1;
+			}
+		}
+
+		if (!detected) {
+			if (digit && aplitude_ok && twist_ok) {
+				if (count == 0) {
+					memset(&dtmf->meas, 0, sizeof(dtmf->meas));
+				}
+				if (count >= time_meas) {
+					dtmf->meas.frequency_low += f1;
+					dtmf->meas.frequency_high += f2;
+					dtmf->meas.amplitude_low += amplitude_low[i];
+					dtmf->meas.amplitude_high += amplitude_high[i];
+					dtmf->meas.count++;
+				}
+				count++;
+				if (count >= time_detect) {
+					detected = digit;
+					dtmf->meas.frequency_low /= dtmf->meas.count;
+					dtmf->meas.frequency_high /= dtmf->meas.count;
+					dtmf->meas.amplitude_low /= dtmf->meas.count;
+					dtmf->meas.amplitude_high /= dtmf->meas.count;
+					dtmf->meas.count = 1;
+					dtmf->recv_digit(dtmf->priv, digit, &dtmf->meas);
+				}
+			} else
+				count = 0;
+		} else {
+			if (!digit || digit != detected || !aplitude_ok || !twist_ok) {
+				count++;
+				if (count >= time_pause) {
+					detected = 0;
+#ifdef DEBUG
+					printf("lost!\n");
+#endif
+				}
+			} else
+				count = 0;
+		}
+#ifdef DEBUG
+		if (digit)
+			printf("DTMF tone='%c' diff frequency=%.1f %.1f amplitude=%.1f %.1f dB (%s) twist=%.1f dB (%s)\n", digit, f1, f2, level2db(amplitude_low[i]), level2db(amplitude_high[i]), (aplitude_ok) ? "OK" : "nok", level2db(amplitude_high[i] / amplitude_low[i]), (twist_ok) ? "OK" : "nok");
+#endif
+
+		dtmf->detected = detected;
+		dtmf->count = count;
+	}
+}
+
--- a/src/libdtmf/dtmf_decode.h
+++ b/src/libdtmf/dtmf_decode.h
@ -0,0 +1,35 @@
+#include "../libfm/fm.h"
+
+typedef struct ftmf_meas {
+	double		frequency_low;
+	double		frequency_high;
+	double		amplitude_low;
+	double		amplitude_high;
+	int		count;
+} dtmf_meas_t;
+
+typedef struct dtmf_dec {
+	void		*priv;
+	void		(*recv_digit)(void *priv, char digit, dtmf_meas_t *meas);
+	int		samplerate;		/* samplerate */
+	double		freq_tollerance;	/* +- limit of frequency deviation to allow */
+	double		min_amplitude;		/* minimum amplitude relative to 0 dBm */
+	double		max_amplitude;		/* maximum amplitude relative to 0 dBm */
+	double		forward_twist;		/* how much do higher frequencies are louder than lower frequencies */
+	double		reverse_twist;		/* how much do lower frequencies are louder than higher frequencies */
+	int		time_detect;
+	int		time_meas;
+	int		time_pause;
+	fm_demod_t	demod_low;		/* demodulator for low frequencies */
+	fm_demod_t	demod_high;		/* demodulator for high frequencies */
+	iir_filter_t	freq_lp[2];		/* low pass to filter the frequency result */
+	char		detected;		/* currently detected DTMF digit or 0 for no detection */
+	int		count;			/* counter to count detection or loss (pause) of signal */
+	dtmf_meas_t	meas;			/* measurements */
+} dtmf_dec_t;
+
+int dtmf_decode_init(dtmf_dec_t *dtmf, void *priv, void (*recv_digit)(void *priv, char digit, dtmf_meas_t *meas), int samplerate, double max_amplitude, double min_amplitude);
+void dtmf_decode_exit(dtmf_dec_t *dtmf);
+void dtmf_decode(dtmf_dec_t *dtmf, sample_t *samples, int length);
+void dtmf_decode_filter(dtmf_dec_t *dtmf, sample_t *samples, int length, sample_t *frequency_low, sample_t *frequency_high, sample_t *amplitude_low, sample_t *amplitude_high);
+
--- a/src/test/Makefile.am
+++ b/src/test/Makefile.am
@ -5,6 +5,7 @@ noinst_PROGRAMS = \
 	test_sendevolumenregler \
 	test_compandor \
 	test_emphasis \
+	test_dtmf \
 	test_dms \
 	test_sms \
 	test_performance \
@ -80,6 +81,15 @@ test_emphasis_LDADD += \
 	$(SOAPY_LIBS)
 endif

+test_dtmf_SOURCES = dummy.x test_dtmf.c
+
+test_dtmf_LDADD = \
+	$(COMMON_LA) \
+	$(top_builddir)/src/libdtmf/libdtmf.a \
+	$(top_builddir)/src/libfm/libfm.a \
+	$(top_builddir)/src/libfilter/libfilter.a \
+	-lm
+
 test_dms_SOURCES = test_dms.c dummy.c

 test_dms_LDADD = \
--- a/src/test/test_dtmf.c
+++ b/src/test/test_dtmf.c
@ -0,0 +1,114 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <math.h>
+#include <string.h>
+#include "../libdebug/debug.h"
+#include "../libsample/sample.h"
+#include "../libdtmf/dtmf_decode.h"
+#include "../libdtmf/dtmf_encode.h"
+
+#define level2db(level)		(20 * log10(level))
+#define db2level(db)		pow(10, (double)db / 20.0)
+
+#define SAMPLERATE		8000
+
+static double test_frequency[8] = { 697.0, 770.0, 852.0, 941.0, 1209.0, 1336.0, 1477.0, 1633.0 };
+static const char *test_digits = "*#0123456789ABCD";
+
+static sample_t samples[SAMPLERATE];
+
+/* generate samples with two tones */
+static void generate_test_sample(double frequency1, double frequency2, double amplitude1, double amplitude2)
+{
+	int i;
+	double value;
+
+	for (i = 0; i < SAMPLERATE; i++) {
+		value = cos(2.0 * M_PI * frequency1 / (double)SAMPLERATE * i) * amplitude1;
+		value += cos(2.0 * M_PI * frequency2 / (double)SAMPLERATE * i) * amplitude2;
+		samples[i] = value;
+	}
+}
+
+static void check_level(sample_t *samples, const char *desc, double target, int when1, int when2)
+{
+	int i;
+	double amplitude = 0.0, diff;
+
+	for (i = when1; i < when2; i++) {
+		amplitude += samples[i];
+	}
+	amplitude = amplitude / (when2 - when1);
+	diff = fabs(amplitude - target);
+	printf("%s: amplitude between %d and %d ms is %.4f / %.4f db (expected %.4f)\n", desc, when1 * 1000 / SAMPLERATE, when2 * 1000 / SAMPLERATE, amplitude, level2db(amplitude), level2db(target));
+	if (diff < -0.1 || diff > 0.1)
+		printf("**** ERROR: we expected a diff close to 0.0\n");
+	else
+		printf("OK!\n");
+}
+
+static char got_digit;
+
+static void recv_digit(void *inst, char digit, dtmf_meas_t *meas)
+{
+	printf("decoded digit '%c'  frequency %.1f %.1f  amplitude %.1f %.1f dB\n", digit, meas->frequency_low, meas->frequency_high, level2db(meas->amplitude_low), level2db(meas->amplitude_high));
+	got_digit = digit;
+}
+
+int main(void)
+{
+	dtmf_dec_t dtmf_dec;
+	dtmf_enc_t dtmf_enc;
+	sample_t frequency1[SAMPLERATE], frequency2[SAMPLERATE], amplitude1[SAMPLERATE], amplitude2[SAMPLERATE];
+	int f, i;
+	double target;
+
+	dtmf_decode_init(&dtmf_dec, NULL, recv_digit, SAMPLERATE, db2level(0), db2level(-30.0));
+
+	for (f = 0; f < 8; f++) {
+		printf("Testing filter with frequency %.0f Hz:\n", test_frequency[f]);
+		generate_test_sample(test_frequency[f], 0.0, 1.0, 0.0);
+
+		dtmf_decode_filter(&dtmf_dec, samples, SAMPLERATE, frequency1, frequency2, amplitude1, amplitude2);
+
+		if (f == 0 || f == 3)
+			target = sqrt(0.5);
+		else if (f == 1 || f == 2)
+			target = 1.0;
+		else
+			target = 0.0;
+		check_level(amplitude1, "frequency level", target, 900 * SAMPLERATE / 1000, 1000 * SAMPLERATE / 1000);
+		if (f == 4 || f == 7)
+			target = sqrt(0.5);
+		else if (f == 5 || f == 6)
+			target = 1.0;
+		else
+			target = 0.0;
+		check_level(amplitude2, "frequency level", target, 900 * SAMPLERATE / 1000, 1000 * SAMPLERATE / 1000);
+
+		puts("");
+	}
+
+	dtmf_encode_init(&dtmf_enc, SAMPLERATE, 1.0);
+
+	for (i = 0; i < 16; i++) {
+		printf("Testing digit '%c' encoding and decoding:\n", test_digits[i]);
+		memset(samples, 0, sizeof(samples[0]) * SAMPLERATE);
+		dtmf_encode_set_tone(&dtmf_enc, test_digits[i]);
+		dtmf_encode(&dtmf_enc, samples + SAMPLERATE / 10, SAMPLERATE / 20);
+		got_digit = 0;
+		dtmf_decode(&dtmf_dec, samples, SAMPLERATE);
+		if (got_digit == 0)
+			printf("**** ERROR: we expected to decode digit '%c', but nothing was decoded\n", test_digits[i]);
+		else if (got_digit != test_digits[i])
+			printf("**** ERROR: we expected to decode digit '%c', but we decoded digit '%c'\n", test_digits[i], got_digit);
+		else
+			printf("OK!\n");
+		puts("");
+	}
+
+	dtmf_decode_exit(&dtmf_dec);
+
+	return 0;
+}
+