143 lines
3.7 KiB
C
143 lines
3.7 KiB
C
/* Sample rate conversion
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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 <stdio.h>
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#include <stdint.h>
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#include <errno.h>
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#include <string.h>
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#include <stdlib.h>
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#include "samplerate.h"
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/* NOTE: This is quick and dirtry. */
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int init_samplerate(samplerate_t *state, double samplerate)
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{
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#if 0
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if ((samplerate % 8000)) {
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fprintf(stderr, "Sample rate must be a muliple of 8000 to support MNCC socket interface, aborting!\n");
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return -EINVAL;
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}
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#endif
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memset(state, 0, sizeof(*state));
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state->factor = samplerate / 8000.0;
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filter_lowpass_init(&state->up.lp, 4000.0, samplerate);
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filter_lowpass_init(&state->down.lp, 4000.0, samplerate);
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return 0;
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}
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/* convert input sample rate to 8000 Hz */
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int samplerate_downsample(samplerate_t *state, int16_t *input, int input_num, int16_t *output)
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{
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int output_num = 0, i, idx;
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double factor = state->factor, in_index;
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double spl[input_num];
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int32_t value;
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/* convert samples to double */
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for (i = 0; i < input_num; i++)
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spl[i] = *input++ / 32768.0;
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/* filter down */
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filter_lowpass_process(&state->down.lp, spl, input_num, 1);
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/* resample filtered result */
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in_index = state->down.in_index;
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for (i = 0; ; i++) {
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/* convert index to int */
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idx = (int)in_index;
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/* if index is outside input sample range, we are done */
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if (idx >= input_num)
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break;
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/* copy value from input to output */
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value = spl[idx] * 32768.0;
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if (value < -32768)
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value = -32768;
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else if (value > 32767)
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value = 32767;
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*output++ = value;
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/* count output number */
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output_num++;
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/* increment input index */
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in_index += factor;
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}
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/* remove number of input samples from index */
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in_index -= (double)input_num;
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/* in_index cannot be negative, excpet due to rounding error, so... */
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if ((int)in_index < 0)
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in_index = 0.0;
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state->down.in_index = in_index;
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return output_num;
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}
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/* convert 8000 Hz sample rate to output sample rate */
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int samplerate_upsample(samplerate_t *state, int16_t *input, int input_num, int16_t *output)
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{
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int output_num = 0, i, idx;
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double factor = 1.0 / state->factor, in_index;
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double spl[(int)((double)input_num / factor + 0.5) + 10]; /* add some fafety */
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int32_t value;
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/* resample input */
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in_index = state->up.in_index;
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for (i = 0; ; i++) {
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/* convert index to int */
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idx = (int)in_index;
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/* if index is outside input sample range, we are done */
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if (idx >= input_num)
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break;
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/* copy value */
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spl[i] = input[idx] / 32768.0;
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/* count output number */
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output_num++;
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/* increment input index */
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in_index += factor;
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}
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/* remove number of input samples from index */
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in_index -= (double)input_num;
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/* in_index cannot be negative, excpet due to rounding error, so... */
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if ((int)in_index < 0)
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in_index = 0.0;
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state->up.in_index = in_index;
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/* filter up */
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filter_lowpass_process(&state->up.lp, spl, output_num, 1);
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/* convert double to samples */
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for (i = 0; i < output_num; i++) {
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value = spl[i] * 32768.0;
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if (value < -32768)
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value = -32768;
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else if (value > 32767)
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value = 32767;
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*output++ = value;
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}
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return output_num;
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}
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