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/* Goertzel functions
*
* (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 <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <math.h>
#include "../common/debug.h"
#include "goertzel.h"
/*
* audio level calculation
*/
/* return average value (rectified value), that can be 0..1 */
double audio_level(int16_t *samples, int length)
{
int32_t bias;
double level;
int sk;
int n;
/* calculate bias */
bias = 0;
for (n = 0; n < length; n++)
bias += samples[n];
bias = bias / length;
/* level calculation */
level = 0;
for (n = 0; n < length; n++) {
sk = samples[n] - bias;
if (sk < 0)
level -= (double)sk;
if (sk > 0)
level += (double)sk;
}
level = level / (double)length / 32767.0;
return level;
}
/*
* goertzel filter
*/
/* filter frequencies and return their levels
*
* samples: pointer to sample buffer
* length: length of buffer
* offset: for ring buffer, start here and wrap arround to 0 when length has been hit
* coeff: array of coefficients (coeff << 15)
* result: array of result levels (average value of the sine, that is 1 / (PI/2) of the sine's peak)
* k: number of frequencies to check
*/
void audio_goertzel(int16_t *samples, int length, int offset, int *coeff, double *result, int k)
{
int32_t bias;
int32_t sk, sk1, sk2;
int64_t cos2pik;
int i, n;
/* calculate bias to remove DC */
bias = 0;
for (n = 0; n < length; n++)
bias += samples[n];
bias = bias / length;
/* we do goertzel */
for (i = 0; i < k; i++) {
sk = 0;
sk1 = 0;
sk2 = 0;
cos2pik = coeff[i];
/* note: after 'length' cycles, offset is restored to its initial value */
for (n = 0; n < length; n++) {
sk = ((cos2pik * sk1) >> 15) - sk2 + samples[offset++] - bias;
sk2 = sk1;
sk1 = sk;
if (offset == length)
offset = 0;
}
/* compute level of signal */
result[i] = sqrt(
((double)sk * (double)sk) -
((double)((cos2pik * sk) >> 15) * (double)sk2) +
((double)sk2 * (double)sk2)
) / (double)length / 32767.0 * 2.0 * 0.63662; /* 1 / (PI/2) */
}
}
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