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annotate mgw/dtmf_init.c @ 171:4f1f3f799295

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doc/Codec-library-depend: article written
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 21 Nov 2022 01:01:39 -0800
parents 815e4c59162e
children
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815e4c59162e mgw DTMF: tone definitions and sample array generation
Mychaela Falconia <falcon@freecalypso.org>
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1 /*
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2 * The code in this module executes once upon themwi-mgw startup;
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3 * it initializes the arrays of linear PCM samples for DTMF output.
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4 *
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5 * The amplitudes of the two sine waves comprising each DTMF tone
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6 * are also defined here.
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7 */
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8
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9 #include <math.h>
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10 #include <stdio.h>
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11 #include <stdint.h>
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12 #include <stdlib.h>
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13 #include "dtmf_defs.h"
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14 #include "int_defs.h"
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15
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16 #define DTMF_AMPL_LOW_TONE 5000
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17 #define DTMF_AMPL_HIGH_TONE 6000
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18
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19 extern struct dtmf_desc dtmf_table[];
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20
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21 static void
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22 init_one_dtmf(desc)
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23 struct dtmf_desc *desc;
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24 {
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25 float angle_low, angle_high;
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26 unsigned n;
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27 int16_t *samp;
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28
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29 angle_low = 0;
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30 angle_high = 0;
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31 samp = desc->samples;
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32 for (n = 0; n < DTMF_MAX_FRAMES * SAMPLES_PER_FRAME; n++) {
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33 *samp++ = sinf(angle_low) * DTMF_AMPL_LOW_TONE +
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34 sinf(angle_high) * DTMF_AMPL_HIGH_TONE;
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35 angle_low += desc->freq_low;
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36 angle_high += desc->freq_high;
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37 }
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38 }
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39
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40 dtmf_init_sample_arrays()
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41 {
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42 struct dtmf_desc *desc;
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43
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44 for (desc = dtmf_table; desc->digit; desc++) {
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45 desc->samples =
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46 malloc(DTMF_MAX_FRAMES * SAMPLES_PER_FRAME * sizeof(int16_t));
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47 if (!desc->samples) {
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48 perror("malloc for DTMF samples");
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49 exit(1);
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50 }
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51 init_one_dtmf(desc);
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52 }
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53 return 0;
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54 }