103 lines
2.5 KiB
C
103 lines
2.5 KiB
C
/* Pre-Emphasis and De-Emphasis implementation
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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 <string.h>
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#include <math.h>
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#include "emphasis.h"
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#include "debug.h"
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int init_emphasis(emphasis_t *state, int samplerate)
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{
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double factor;
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memset(state, 0, sizeof(*state));
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if (samplerate < 24000) {
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PDEBUG(DDSP, DEBUG_ERROR, "Sample rate must be at least 24000 Hz!\n");
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return -1;
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}
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factor = 0.95;
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state->p.factor = factor;
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state->p.amp = samplerate / 48000.0 * 4.0; /* mysterious 48000 */
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state->d.factor = factor;
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state->d.amp = 1.0 / (samplerate / 48000.0 * 4.0); /* mysterious 48000 */
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return 0;
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}
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void pre_emphasis(emphasis_t *state, int16_t *samples, int num)
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{
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int32_t sample;
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double old_value, new_value, last_value, factor, amp;
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int i;
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last_value = state->p.last_value;
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factor = state->p.factor;
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amp = state->p.amp;
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for (i = 0; i < num; i++) {
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old_value = (double)(*samples) / 32768.0;
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new_value = old_value - factor * last_value;
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last_value = old_value;
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sample = (int)(amp * new_value * 32768.0);
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if (sample > 32767)
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sample = 32767;
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else if (sample < -32768)
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sample = -32768;
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*samples++ = sample;
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}
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state->p.last_value = last_value;
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}
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void de_emphasis(emphasis_t *state, int16_t *samples, int num)
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{
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int32_t sample;
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double old_value, new_value, last_value, factor, amp;
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int i;
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last_value = state->d.last_value;
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factor = state->d.factor;
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amp = state->d.amp;
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for (i = 0; i < num; i++) {
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old_value = (double)(*samples) / 32768.0;
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new_value = old_value + factor * last_value;
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last_value = new_value;
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sample = (int)(amp * new_value * 32768.0);
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if (sample > 32767)
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sample = 32767;
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else if (sample < -32768)
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sample = -32768;
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*samples++ = sample;
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}
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state->d.last_value = last_value;
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}
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