forked from cellular-infrastructure/osmocom-analog
101 lines
2.5 KiB
C
101 lines
2.5 KiB
C
/* Goertzel functions
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*
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* (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
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* All Rights Reserved
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include <errno.h>
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#include <math.h>
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#include "../common/debug.h"
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#include "goertzel.h"
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/*
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* audio level calculation
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*/
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/* return average value (rectified value), that can be 0..1 */
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double audio_level(int16_t *samples, int length)
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{
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int bias;
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double level;
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int sk;
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int n;
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/* level calculation */
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bias = 0;
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for (n = 0; n < length; n++)
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bias += samples[n];
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bias = bias / length;
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level = 0;
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for (n = 0; n < length; n++) {
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sk = samples[n] - bias;
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if (sk < 0)
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level -= (double)sk;
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if (sk > 0)
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level += (double)sk;
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}
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level = level / (double)length / 32767.0;
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return level;
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}
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/*
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* goertzel filter
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*/
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/* filter frequencies and return their levels
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*
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* samples: pointer to sample buffer
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* length: length of buffer
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* offset: for ring buffer, start here and wrap arround to 0 when length has been hit
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* coeff: array of coefficients (coeff << 15)
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* result: array of result levels (average value of the sine, that is 1 / (PI/2) of the sine's peak)
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* k: number of frequencies to check
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*/
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void audio_goertzel(int16_t *samples, int length, int offset, int *coeff, double *result, int k)
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{
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int32_t sk, sk1, sk2;
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int64_t cos2pik;
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int i, n;
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/* we do goertzel */
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for (i = 0; i < k; i++) {
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sk = 0;
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sk1 = 0;
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sk2 = 0;
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cos2pik = coeff[i];
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/* note: after 'length' cycles, offset is restored to its initial value */
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for (n = 0; n < length; n++) {
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sk = ((cos2pik * sk1) >> 15) - sk2 + samples[offset++];
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sk2 = sk1;
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sk1 = sk;
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if (offset == length)
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offset = 0;
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}
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/* compute level of signal */
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result[i] = sqrt(
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((double)sk * (double)sk) -
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((double)((cos2pik * sk) >> 15) * (double)sk2) +
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((double)sk2 * (double)sk2)
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) / (double)length / 32767.0 * 2.0 * 0.63662; /* 1 / (PI/2) */
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}
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}
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