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common: Add pre and de emphasis, if the radio does not support it

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Connect to the oscillator of the transmitter - good girl!
You need to enable pre emphasis in this case.

Connect to the discriminator of the receiver - good boy!
You need to enable de emphasis in this case.
This commit is contained in:
Andreas Eversberg
2016-04-23 18:50:11 +02:00
parent 5062628e52
commit 4356c93afa
20 changed files with 256 additions and 19 deletions
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102
src/common/emphasis.c Normal file
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/* Pre-Emphasis and De-Emphasis implementation
*
* (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 <stdio.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include "emphasis.h"
#include "debug.h"
int init_emphasis(emphasis_t *state, int samplerate)
{
double factor;
memset(state, 0, sizeof(*state));
if (samplerate < 24000) {
PDEBUG(DDSP, DEBUG_ERROR, "Sample rate must be at least 24000 Hz!\n");
return -1;
}
factor = 0.95;
state->p.factor = factor;
state->p.amp = samplerate / 48000.0 * 4.0; /* mysterious 48000 */
state->d.factor = factor;
state->d.amp = 1.0 / (samplerate / 48000.0 * 4.0); /* mysterious 48000 */
return 0;
}
void pre_emphasis(emphasis_t *state, int16_t *samples, int num)
{
int32_t sample;
double old_value, new_value, last_value, factor, amp;
int i;
last_value = state->p.last_value;
factor = state->p.factor;
amp = state->p.amp;
for (i = 0; i < num; i++) {
old_value = (double)(*samples) / 32768.0;
new_value = old_value - factor * last_value;
last_value = old_value;
sample = (int)(amp * new_value * 32768.0);
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
sample = -32768;
*samples++ = sample;
}
state->p.last_value = last_value;
}
void de_emphasis(emphasis_t *state, int16_t *samples, int num)
{
int32_t sample;
double old_value, new_value, last_value, factor, amp;
int i;
last_value = state->d.last_value;
factor = state->d.factor;
amp = state->d.amp;
for (i = 0; i < num; i++) {
old_value = (double)(*samples) / 32768.0;
new_value = old_value + factor * last_value;
last_value = new_value;
sample = (int)(amp * new_value * 32768.0);
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
sample = -32768;
*samples++ = sample;
}
state->d.last_value = last_value;
}