libteletone_detect.c File Reference

#include <libteletone_detect.h>
#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <time.h>
#include <fcntl.h>

Include dependency graph for libteletone_detect.c:

Go to the source code of this file.

Macros
#define	LOW_ENG   10000000
#define	ZC   2
#define	teletone_goertzel_result(gs)   (double)(((gs)->v3 * (gs)->v3 + (gs)->v2 * (gs)->v2 - (gs)->v2 * (gs)->v3 * (gs)->fac))

Functions
static void	goertzel_init (teletone_goertzel_state_t *goertzel_state, teletone_detection_descriptor_t *tdesc)
void	teletone_goertzel_update (teletone_goertzel_state_t *goertzel_state, int16_t sample_buffer[], int samples)
	Step through the Goertzel Algorithm for each sample in a buffer. More...
void	teletone_dtmf_detect_init (teletone_dtmf_detect_state_t *dtmf_detect_state, int sample_rate)
	Initilize a DTMF detection state object. More...
void	teletone_multi_tone_init (teletone_multi_tone_t *mt, teletone_tone_map_t *map)
	Initilize a multi-frequency tone detector. More...
int	teletone_multi_tone_detect (teletone_multi_tone_t *mt, int16_t sample_buffer[], int samples)
	Check a sample buffer for the presence of the mulit-frequency tone described by mt. More...
teletone_hit_type_t	teletone_dtmf_detect (teletone_dtmf_detect_state_t *dtmf_detect_state, int16_t sample_buffer[], int samples)
	Check a sample buffer for the presence of DTMF digits. More...
int	teletone_dtmf_get (teletone_dtmf_detect_state_t *dtmf_detect_state, char *buf, unsigned int *dur)
	retrieve any collected digits into a string buffer More...

Variables
static teletone_detection_descriptor_t	dtmf_detect_row [GRID_FACTOR]
static teletone_detection_descriptor_t	dtmf_detect_col [GRID_FACTOR]
static teletone_detection_descriptor_t	dtmf_detect_row_2nd [GRID_FACTOR]
static teletone_detection_descriptor_t	dtmf_detect_col_2nd [GRID_FACTOR]
static float	dtmf_row [] = {697.0f, 770.0f, 852.0f, 941.0f}
static float	dtmf_col [] = {1209.0f, 1336.0f, 1477.0f, 1633.0f}
static char	dtmf_positions [] = "123A" "456B" "789C" "*0#D"

Macro Definition Documentation

LOW_ENG

#define LOW_ENG   10000000

Definition at line 103 of file libteletone_detect.c.

Referenced by teletone_dtmf_detect().

teletone_goertzel_result

#define teletone_goertzel_result

(

gs

)

(double)(((gs)->v3 * (gs)->v3 + (gs)->v2 * (gs)->v2 - (gs)->v2 * (gs)->v3 * (gs)->fac))

Definition at line 137 of file libteletone_detect.c.

Referenced by teletone_dtmf_detect(), and teletone_multi_tone_detect().

ZC

#define ZC   2

Definition at line 104 of file libteletone_detect.c.

Referenced by teletone_dtmf_detect().

Function Documentation

goertzel_init()

static void goertzel_init ( teletone_goertzel_state_t *  goertzel_state, teletone_detection_descriptor_t *  tdesc  )

static

Definition at line 115 of file libteletone_detect.c.

References teletone_goertzel_state_t::fac, teletone_detection_descriptor_t::fac, teletone_goertzel_state_t::v2, and teletone_goertzel_state_t::v3.

Referenced by teletone_dtmf_detect(), teletone_dtmf_detect_init(), teletone_multi_tone_detect(), and teletone_multi_tone_init().

                                                                                                             {
        goertzel_state->v2 = goertzel_state->v3 = 0.0;
        goertzel_state->fac = tdesc->fac;
}

teletone_dtmf_detect()

teletone_hit_type_t teletone_dtmf_detect	(	teletone_dtmf_detect_state_t *	dtmf_detect_state,
		int16_t	sample_buffer[],
		int	samples
	)

Check a sample buffer for the presence of DTMF digits.

Parameters

dtmf_detect_state	the detection state object to check
sample_buffer	an array aof 16 bit signed linear samples
samples	the number of samples present in sample_buffer

Returns

true when DTMF was detected or false when it is not

Definition at line 307 of file libteletone_detect.c.

References BLOCK_LEN, teletone_dtmf_detect_state_t::col_out, teletone_dtmf_detect_state_t::col_out2nd, teletone_dtmf_detect_state_t::current_digits, teletone_dtmf_detect_state_t::current_sample, teletone_dtmf_detect_state_t::detected_digits, teletone_dtmf_detect_state_t::digit, teletone_dtmf_detect_state_t::digit_hits, DTMF_2ND_HARMONIC_COL, DTMF_2ND_HARMONIC_ROW, DTMF_NORMAL_TWIST, dtmf_positions, DTMF_RELATIVE_PEAK_COL, DTMF_RELATIVE_PEAK_ROW, DTMF_REVERSE_TWIST, DTMF_THRESHOLD, teletone_dtmf_detect_state_t::dur, teletone_dtmf_detect_state_t::energy, teletone_goertzel_state_t::fac, goertzel_init(), GRID_FACTOR, teletone_dtmf_detect_state_t::hit1, teletone_dtmf_detect_state_t::hit2, teletone_dtmf_detect_state_t::hit3, teletone_dtmf_detect_state_t::lenergy, teletone_dtmf_detect_state_t::lost_digits, LOW_ENG, teletone_dtmf_detect_state_t::row_out, teletone_dtmf_detect_state_t::row_out2nd, teletone_goertzel_result, TELETONE_MAX_DTMF_DIGITS, TT_HIT_BEGIN, TT_HIT_END, TT_HIT_MIDDLE, teletone_goertzel_state_t::v2, teletone_goertzel_state_t::v3, ZC, and teletone_dtmf_detect_state_t::zc.

Referenced by inband_dtmf_callback().

{
        float row_energy[GRID_FACTOR];
        float col_energy[GRID_FACTOR];
        float famp;
        float v1;
        int i;
        int j;
        int sample;
        int best_row;
        int best_col;
        char hit = 0;
        int limit;
        teletone_hit_type_t r = 0;

        for (sample = 0;  sample < samples;      sample = limit) {
                /* BLOCK_LEN is optimised to meet the DTMF specs. */
                if ((samples - sample) >= (BLOCK_LEN - dtmf_detect_state->current_sample)) {
                        limit = sample + (BLOCK_LEN - dtmf_detect_state->current_sample);
                } else {
                        limit = samples;
                }

                for (j = sample;  j < limit;  j++) {
                        int x = 0;
                        famp = sample_buffer[j];
                        
                        dtmf_detect_state->energy += famp*famp;

                        for(x = 0; x < GRID_FACTOR; x++) {
                                v1 = dtmf_detect_state->row_out[x].v2;
                                dtmf_detect_state->row_out[x].v2 = dtmf_detect_state->row_out[x].v3;
                                dtmf_detect_state->row_out[x].v3 = (float)(dtmf_detect_state->row_out[x].fac*dtmf_detect_state->row_out[x].v2 - v1 + famp);
        
                                v1 = dtmf_detect_state->col_out[x].v2;
                                dtmf_detect_state->col_out[x].v2 = dtmf_detect_state->col_out[x].v3;
                                dtmf_detect_state->col_out[x].v3 = (float)(dtmf_detect_state->col_out[x].fac*dtmf_detect_state->col_out[x].v2 - v1 + famp);

                                v1 = dtmf_detect_state->col_out2nd[x].v2;
                                dtmf_detect_state->col_out2nd[x].v2 = dtmf_detect_state->col_out2nd[x].v3;
                                dtmf_detect_state->col_out2nd[x].v3 = (float)(dtmf_detect_state->col_out2nd[x].fac*dtmf_detect_state->col_out2nd[x].v2 - v1 + famp);
                
                                v1 = dtmf_detect_state->row_out2nd[x].v2;
                                dtmf_detect_state->row_out2nd[x].v2 = dtmf_detect_state->row_out2nd[x].v3;
                                dtmf_detect_state->row_out2nd[x].v3 = (float)(dtmf_detect_state->row_out2nd[x].fac*dtmf_detect_state->row_out2nd[x].v2 - v1 + famp);
                        }

                }

                if (dtmf_detect_state->zc > 0) {
                        if (dtmf_detect_state->energy < LOW_ENG && dtmf_detect_state->lenergy < LOW_ENG) {
                                if (!--dtmf_detect_state->zc) {
                                        /* Reinitialise the detector for the next block */
                                        dtmf_detect_state->hit1 = dtmf_detect_state->hit2 = 0;
                                        for (i = 0;      i < GRID_FACTOR;  i++) {
                                                goertzel_init (&dtmf_detect_state->row_out[i], &dtmf_detect_row[i]);
                                                goertzel_init (&dtmf_detect_state->col_out[i], &dtmf_detect_col[i]);
                                                goertzel_init (&dtmf_detect_state->row_out2nd[i], &dtmf_detect_row_2nd[i]);
                                                goertzel_init (&dtmf_detect_state->col_out2nd[i], &dtmf_detect_col_2nd[i]);
                                        }
                                        dtmf_detect_state->dur -= samples;
                                        return TT_HIT_END;
                                }
                        }
                        
                        dtmf_detect_state->dur += samples;
                        dtmf_detect_state->lenergy = dtmf_detect_state->energy;
                        dtmf_detect_state->energy = 0.0;
                        dtmf_detect_state->current_sample = 0;
                        return TT_HIT_MIDDLE;
                } else if (dtmf_detect_state->digit) {
                        return TT_HIT_END;
                }
                

                dtmf_detect_state->current_sample += (limit - sample);
                if (dtmf_detect_state->current_sample < BLOCK_LEN) {
                        continue;
                }
                /* We are at the end of a DTMF detection block */
                /* Find the peak row and the peak column */
                row_energy[0] = teletone_goertzel_result (&dtmf_detect_state->row_out[0]);
                col_energy[0] = teletone_goertzel_result (&dtmf_detect_state->col_out[0]);

                for (best_row = best_col = 0, i = 1;  i < GRID_FACTOR;  i++) {
                        row_energy[i] = teletone_goertzel_result (&dtmf_detect_state->row_out[i]);
                        if (row_energy[i] > row_energy[best_row]) {
                                best_row = i;
                        }
                        col_energy[i] = teletone_goertzel_result (&dtmf_detect_state->col_out[i]);
                        if (col_energy[i] > col_energy[best_col]) {
                                best_col = i;
                        }
                }
                hit = 0;
                /* Basic signal level test and the twist test */
                if (row_energy[best_row] >= DTMF_THRESHOLD &&
                        col_energy[best_col] >= DTMF_THRESHOLD &&
                        col_energy[best_col] < row_energy[best_row]*DTMF_REVERSE_TWIST &&
                        col_energy[best_col]*DTMF_NORMAL_TWIST > row_energy[best_row]) {
                        /* Relative peak test */
                        for (i = 0;      i < GRID_FACTOR;  i++) {
                                if ((i != best_col      &&      col_energy[i]*DTMF_RELATIVE_PEAK_COL > col_energy[best_col]) ||
                                        (i != best_row  &&      row_energy[i]*DTMF_RELATIVE_PEAK_ROW > row_energy[best_row])) {
                                        break;
                                }
                        }
                        /* ... and second harmonic test */
                        if (i >= GRID_FACTOR && (row_energy[best_row] + col_energy[best_col]) > 42.0*dtmf_detect_state->energy &&
                                teletone_goertzel_result (&dtmf_detect_state->col_out2nd[best_col])*DTMF_2ND_HARMONIC_COL < col_energy[best_col] &&
                                teletone_goertzel_result (&dtmf_detect_state->row_out2nd[best_row])*DTMF_2ND_HARMONIC_ROW < row_energy[best_row]) {
                                hit = dtmf_positions[(best_row << 2) + best_col];
                                /* Look for two successive similar results */
                                /* The logic in the next test is:
                                   We need two successive identical clean detects, with
                                   something different preceeding it. This can work with
                                   back to back differing digits. More importantly, it
                                   can work with nasty phones that give a very wobbly start
                                   to a digit. */
                                if (! r && hit == dtmf_detect_state->hit3 && dtmf_detect_state->hit3 != dtmf_detect_state->hit2) {
                                        dtmf_detect_state->digit_hits[(best_row << 2) + best_col]++;
                                        dtmf_detect_state->detected_digits++;
                                        if (dtmf_detect_state->current_digits < TELETONE_MAX_DTMF_DIGITS) {
                                                dtmf_detect_state->digit = hit;
                                        } else {
                                                dtmf_detect_state->lost_digits++;
                                        }
                                        
                                        if (!dtmf_detect_state->zc) {
                                                dtmf_detect_state->zc = ZC;
                                                dtmf_detect_state->dur = 0;
                                                r = TT_HIT_BEGIN;
                                                break;
                                        }                                       

                                }
                        }
                }

                dtmf_detect_state->hit1 = dtmf_detect_state->hit2;
                dtmf_detect_state->hit2 = dtmf_detect_state->hit3;
                dtmf_detect_state->hit3 = hit;

                dtmf_detect_state->energy = 0.0;
                dtmf_detect_state->current_sample = 0;
                
        }

        return r;
}

teletone_dtmf_detect_init()

void teletone_dtmf_detect_init	(	teletone_dtmf_detect_state_t *	dtmf_detect_state,
		int	sample_rate
	)

Initilize a DTMF detection state object.

Parameters

dtmf_detect_state	the DTMF detection state to initilize
sample_rate	the desired sample rate

Definition at line 139 of file libteletone_detect.c.

References teletone_dtmf_detect_state_t::col_out, teletone_dtmf_detect_state_t::col_out2nd, teletone_dtmf_detect_state_t::current_sample, teletone_dtmf_detect_state_t::detected_digits, teletone_dtmf_detect_state_t::digit, dtmf_col, dtmf_row, teletone_dtmf_detect_state_t::dur, teletone_dtmf_detect_state_t::energy, teletone_detection_descriptor_t::fac, goertzel_init(), GRID_FACTOR, teletone_dtmf_detect_state_t::hit1, teletone_dtmf_detect_state_t::hit2, teletone_dtmf_detect_state_t::lost_digits, M_TWO_PI, teletone_dtmf_detect_state_t::row_out, and teletone_dtmf_detect_state_t::row_out2nd.

Referenced by switch_ivr_inband_dtmf_session().

{
        int i;
        float theta;

        if (!sample_rate) {
                sample_rate = 8000;
        }

        dtmf_detect_state->hit1 = dtmf_detect_state->hit2 = 0;

        for (i = 0;      i < GRID_FACTOR;  i++) {
                theta = (float)(M_TWO_PI*(dtmf_row[i]/(float)sample_rate));
                dtmf_detect_row[i].fac = (float)(2.0*cos(theta));

                theta = (float)(M_TWO_PI*(dtmf_col[i]/(float)sample_rate));
                dtmf_detect_col[i].fac = (float)(2.0*cos(theta));
        
                theta = (float)(M_TWO_PI*(dtmf_row[i]*2.0/(float)sample_rate));
                dtmf_detect_row_2nd[i].fac = (float)(2.0*cos(theta));

                theta = (float)(M_TWO_PI*(dtmf_col[i]*2.0/(float)sample_rate));
                dtmf_detect_col_2nd[i].fac = (float)(2.0*cos(theta));
        
                goertzel_init (&dtmf_detect_state->row_out[i], &dtmf_detect_row[i]);
                goertzel_init (&dtmf_detect_state->col_out[i], &dtmf_detect_col[i]);
                goertzel_init (&dtmf_detect_state->row_out2nd[i], &dtmf_detect_row_2nd[i]);
                goertzel_init (&dtmf_detect_state->col_out2nd[i], &dtmf_detect_col_2nd[i]);
        
                dtmf_detect_state->energy = 0.0;
        }
        dtmf_detect_state->current_sample = 0;
        dtmf_detect_state->detected_digits = 0;
        dtmf_detect_state->lost_digits = 0;
        dtmf_detect_state->digit = 0;
        dtmf_detect_state->dur = 0;
}

teletone_dtmf_get()

int teletone_dtmf_get	(	teletone_dtmf_detect_state_t *	dtmf_detect_state,
		char *	buf,
		unsigned int *	dur
	)

retrieve any collected digits into a string buffer

Parameters

dtmf_detect_state	the detection state object to check
buf	the string buffer to write to
max	the maximum length of buf

Returns

the number of characters written to buf

Definition at line 461 of file libteletone_detect.c.

References teletone_dtmf_detect_state_t::digit, teletone_dtmf_detect_state_t::dur, and teletone_dtmf_detect_state_t::zc.

Referenced by inband_dtmf_callback().

{
        if (!dtmf_detect_state->digit) {
                return 0;
        }

        *buf = dtmf_detect_state->digit;

        *dur = dtmf_detect_state->dur;

        if (!dtmf_detect_state->zc) {
                dtmf_detect_state->dur = 0;
                dtmf_detect_state->digit = 0;
        }
        
        return 1;
}

teletone_goertzel_update()

void teletone_goertzel_update	(	teletone_goertzel_state_t *	goertzel_state,
		int16_t	sample_buffer[],
		int	samples
	)

Step through the Goertzel Algorithm for each sample in a buffer.

Parameters

goertzel_state	the goertzel state to step the samples through
sample_buffer	an array aof 16 bit signed linear samples
samples	the number of samples present in sample_buffer

Definition at line 120 of file libteletone_detect.c.

References teletone_goertzel_state_t::fac, teletone_goertzel_state_t::v2, and teletone_goertzel_state_t::v3.

{
        int i;
        float v1;
        
        for (i = 0;      i < samples;  i++) {
                v1 = goertzel_state->v2;
                goertzel_state->v2 = goertzel_state->v3;
                goertzel_state->v3 = (float)(goertzel_state->fac*goertzel_state->v2 - v1 + sample_buffer[i]);
        }
}

teletone_multi_tone_detect()

int teletone_multi_tone_detect	(	teletone_multi_tone_t *	mt,
		int16_t	sample_buffer[],
		int	samples
	)

Check a sample buffer for the presence of the mulit-frequency tone described by mt.

Parameters

mt	the multi-frequency tone descriptor
sample_buffer	an array aof 16 bit signed linear samples
samples	the number of samples present in sample_buffer

Returns

true when the tone was detected or false when it is not

Definition at line 217 of file libteletone_detect.c.

References teletone_multi_tone_t::current_sample, teletone_multi_tone_t::energy, teletone_goertzel_state_t::fac, goertzel_init(), teletone_multi_tone_t::gs, teletone_multi_tone_t::gs2, teletone_multi_tone_t::hit_factor, teletone_multi_tone_t::hits, teletone_multi_tone_t::min_samples, teletone_multi_tone_t::negative_factor, teletone_multi_tone_t::negatives, teletone_multi_tone_t::positive_factor, teletone_multi_tone_t::positives, teletone_multi_tone_t::tdd, teletone_goertzel_result, TELETONE_MAX_TONES, teletone_multi_tone_t::tone_count, teletone_multi_tone_t::total_samples, teletone_goertzel_state_t::v2, and teletone_goertzel_state_t::v3.

Referenced by tone_detect_callback().

{
        int sample, limit = 0, j, x = 0;
        float v1, famp;
        float eng_sum = 0, eng_all[TELETONE_MAX_TONES] = {0.0};
        int gtest = 0, see_hit = 0;

        for (sample = 0;  sample >= 0 && sample < samples; sample = limit) {
                mt->total_samples++;

                if ((samples - sample) >= (mt->min_samples - mt->current_sample)) {
                        limit = sample + (mt->min_samples - mt->current_sample);
                } else {
                        limit = samples;
                }
                if (limit < 0 || limit > samples) {
                        limit = samples;
                }

                for (j = sample;  j < limit;  j++) {
                        famp = sample_buffer[j];
                        
                        mt->energy += famp*famp;

                        for(x = 0; x < TELETONE_MAX_TONES && x < mt->tone_count; x++) {
                                v1 = mt->gs[x].v2;
                                mt->gs[x].v2 = mt->gs[x].v3;
                                mt->gs[x].v3 = (float)(mt->gs[x].fac * mt->gs[x].v2 - v1 + famp);
        
                                v1 = mt->gs2[x].v2;
                                mt->gs2[x].v2 = mt->gs2[x].v3;
                                mt->gs2[x].v3 = (float)(mt->gs2[x].fac*mt->gs2[x].v2 - v1 + famp);
                        }
                }

                mt->current_sample += (limit - sample);
                if (mt->current_sample < mt->min_samples) {
                        continue;
                }

                eng_sum = 0;
                for(x = 0; x < TELETONE_MAX_TONES && x < mt->tone_count; x++) {
                        eng_all[x] = (float)(teletone_goertzel_result (&mt->gs[x]));
                        eng_sum += eng_all[x];
                }

                gtest = 0;
                for(x = 0; x < TELETONE_MAX_TONES && x < mt->tone_count; x++) {
                        gtest += teletone_goertzel_result (&mt->gs2[x]) < eng_all[x] ? 1 : 0;
                }

                if ((gtest >= 2 || gtest == mt->tone_count) && eng_sum > 42.0 * mt->energy) {
                        if(mt->negatives) {
                                mt->negatives--;
                        }
                        mt->positives++;

                        if(mt->positives >= mt->positive_factor) {
                                mt->hits++;
                        }
                        if (mt->hits >= mt->hit_factor) {
                                see_hit++;
                                mt->positives = mt->negatives = mt->hits = 0;
                        }
                } else {
                        mt->negatives++;
                        if(mt->positives) {
                                mt->positives--;
                        }
                        if(mt->negatives > mt->negative_factor) {
                                mt->positives = mt->hits = 0;
                        }
                }

                /* Reinitialise the detector for the next block */
                for(x = 0; x < TELETONE_MAX_TONES && x < mt->tone_count; x++) {
                        goertzel_init (&mt->gs[x], &mt->tdd[x]);
                        goertzel_init (&mt->gs2[x], &mt->tdd[x]);
                }

                mt->energy = 0.0;
                mt->current_sample = 0;
        }

        return see_hit;
}

teletone_multi_tone_init()

void teletone_multi_tone_init	(	teletone_multi_tone_t *	mt,
		teletone_tone_map_t *	map
	)

Initilize a multi-frequency tone detector.

Parameters

mt	the multi-frequency tone descriptor
map	a representation of the multi-frequency tone

Definition at line 177 of file libteletone_detect.c.

References teletone_detection_descriptor_t::fac, teletone_tone_map_t::freqs, goertzel_init(), teletone_multi_tone_t::gs, teletone_multi_tone_t::gs2, teletone_multi_tone_t::hit_factor, M_TWO_PI, teletone_multi_tone_t::min_samples, teletone_multi_tone_t::negative_factor, teletone_multi_tone_t::positive_factor, teletone_multi_tone_t::sample_rate, teletone_multi_tone_t::tdd, TELETONE_MAX_TONES, and teletone_multi_tone_t::tone_count.

Referenced by switch_ivr_tone_detect_session().

{
        float theta = 0;
        int x = 0;

        if (!mt->sample_rate) {
                mt->sample_rate = 8000;
        }

        if (!mt->min_samples) {
                mt->min_samples = 102;
        }

        mt->min_samples *= (mt->sample_rate / 8000);

        if (!mt->positive_factor) {
                mt->positive_factor = 2;
        }

        if(!mt->negative_factor) {
                mt->negative_factor = 10;
        }

        if (!mt->hit_factor) {
                mt->hit_factor = 2;
        }

        for(x = 0; x < TELETONE_MAX_TONES; x++) {
                if ((int) map->freqs[x] == 0) {
                        break;
                }
                mt->tone_count++;
                theta = (float)(M_TWO_PI*(map->freqs[x]/(float)mt->sample_rate));
                mt->tdd[x].fac = (float)(2.0 * cos(theta));
                goertzel_init (&mt->gs[x], &mt->tdd[x]);
                goertzel_init (&mt->gs2[x], &mt->tdd[x]);
        }

}

Variable Documentation

dtmf_col

float dtmf_col[] = {1209.0f, 1336.0f, 1477.0f, 1633.0f}

static

Definition at line 111 of file libteletone_detect.c.

Referenced by teletone_dtmf_detect_init().

dtmf_detect_col

teletone_detection_descriptor_t dtmf_detect_col[GRID_FACTOR]

static

Definition at line 106 of file libteletone_detect.c.

dtmf_detect_col_2nd

teletone_detection_descriptor_t dtmf_detect_col_2nd[GRID_FACTOR]

static

Definition at line 108 of file libteletone_detect.c.

dtmf_detect_row

teletone_detection_descriptor_t dtmf_detect_row[GRID_FACTOR]

static

Definition at line 105 of file libteletone_detect.c.

dtmf_detect_row_2nd

teletone_detection_descriptor_t dtmf_detect_row_2nd[GRID_FACTOR]

static

Definition at line 107 of file libteletone_detect.c.

dtmf_positions

char dtmf_positions[] = "123A" "456B" "789C" "*0#D"

static

Definition at line 113 of file libteletone_detect.c.

Referenced by teletone_dtmf_detect().

dtmf_row

float dtmf_row[] = {697.0f, 770.0f, 852.0f, 941.0f}

static

Definition at line 110 of file libteletone_detect.c.

Referenced by teletone_dtmf_detect_init().