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-rw-r--r--src/libdtmf/dtmf_decode.c259
1 files changed, 259 insertions, 0 deletions
diff --git a/src/libdtmf/dtmf_decode.c b/src/libdtmf/dtmf_decode.c
new file mode 100644
index 0000000..740d504
--- /dev/null
+++ 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_margin = 1.03; /* 1.8 .. 3.5 % */
+ 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 margin, 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 amplitude_ok, twist_ok;
+ int i;
+
+ margin = dtmf->freq_margin;
+ 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 / margin && f1 <= DTMF_LOW_1 * margin) {
+ /* cutoff point */
+ amplitude_low[i] /= 0.7071;
+ low = 1;
+ f1 -= DTMF_LOW_1;
+ } else
+ if (f1 >= DTMF_LOW_2 / margin && f1 <= DTMF_LOW_2 * margin) {
+ amplitude_low[i] /= 1.0734;
+ low = 2;
+ f1 -= DTMF_LOW_2;
+ } else
+ if (f1 >= DTMF_LOW_3 / margin && f1 <= DTMF_LOW_3 * margin) {
+ amplitude_low[i] /= 1.0389;
+ low = 3;
+ f1 -= DTMF_LOW_3;
+ } else
+ if (f1 >= DTMF_LOW_4 / margin && f1 <= DTMF_LOW_4 * margin) {
+ /* 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 / margin && f2 <= DTMF_HIGH_1 * margin) {
+ /* cutoff point */
+ amplitude_high[i] /= 0.7071;
+ high = 1;
+ f2 -= DTMF_HIGH_1;
+ } else
+ if (f2 >= DTMF_HIGH_2 / margin && f2 <= DTMF_HIGH_2 * margin) {
+ amplitude_high[i] /= 1.0731;
+ high = 2;
+ f2 -= DTMF_HIGH_2;
+ } else
+ if (f2 >= DTMF_HIGH_3 / margin && f2 <= DTMF_HIGH_3 * margin) {
+ amplitude_high[i] /= 1.0372;
+ high = 3;
+ f2 -= DTMF_HIGH_3;
+ } else
+ if (f2 >= DTMF_HIGH_4 / margin && f2 <= DTMF_HIGH_4 * margin) {
+ /* cutoff point */
+ amplitude_high[i] /= 0.7071;
+ high = 4;
+ f2 -= DTMF_HIGH_4;
+ } else
+ high = 0;
+ digit = 0;
+ amplitude_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) {
+ amplitude_ok = 1;
+#ifdef DEBUG
+ printf("%.1f %.1f (limits %.1f .. %.1f) %.1f\n", level2db(amplitude_low[i]), level2db(amplitude_high[i]), level2db(min_amplitude), level2db(max_amplitude), 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 && amplitude_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 || !amplitude_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]), (amplitude_ok) ? "OK" : "nok", level2db(amplitude_high[i] / amplitude_low[i]), (twist_ok) ? "OK" : "nok");
+#endif
+
+ dtmf->detected = detected;
+ dtmf->count = count;
+ }
+}
+
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