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/* 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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