Add compander to common part

pull/1/head
Andreas Eversberg 7 years ago
parent 4ab1cd5026
commit cbfc818cce
  1. 1
      src/common/Makefile.am
  2. 132
      src/common/compander.c
  3. 11
      src/common/compander.h

@ -17,6 +17,7 @@ libcommon_a_SOURCES = \
../common/besetztton.c \
../common/mncc_sock.c \
../common/cause.c \
../common/compander.c \
../common/sender.c \
../common/main_common.c

@ -0,0 +1,132 @@
/* Compander to use various networks like C-Netz / NMT / AMPS
*
* (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 <string.h>
#include <math.h>
#include "compander.h"
/* this is the 0 DB level that stays 0 DB after compression / espansion */
#define ZERO_DB_LEVEL 16384.0
/* what factor shall the gain raise and fall after given attack/recovery time */
#define ATTACK_FACTOR 1.5
#define RECOVERY_FACTOR 0.75
/* Minimum level value to keep state */
#define ENVELOP_MIN 0.001
static double sqrt_tab[10000];
/*
* Generate companding tables according to NMT specification
*
* Hopefully this is correct
*
*/
void init_compander(compander_t *state, int samplerate, double attack_ms, double recovery_ms)
{
int i;
memset(state, 0, sizeof(*state));
state->envelop_e = 1.0;
state->envelop_c = 1.0;
/* ITU-T G.162: 1.5 times the steady state after attack_ms */
state->step_up = pow(ATTACK_FACTOR, 1000.0 / attack_ms / (double)samplerate);
/* ITU-T G.162: 0.75 times the steady state after recovery_ms */
state->step_down = pow(RECOVERY_FACTOR, 1000.0 / recovery_ms / (double)samplerate);
// FIXME: make global, not at instance
for (i = 0; i < 10000; i++)
sqrt_tab[i] = sqrt(i * 0.001);
}
void compress_audio(compander_t *state, int16_t *samples, int num)
{
int32_t sample;
double value, envelop, step_up, step_down;
int i;
step_up = state->step_up;
step_down = state->step_down;
envelop = state->envelop_c;
// printf("envelop=%.4f\n", envelop);
for (i = 0; i < num; i++) {
/* normalize sample value to 0 DB level */
value = (double)(*samples) / ZERO_DB_LEVEL;
if (fabs(value) > envelop)
envelop *= step_up;
else
envelop *= step_down;
if (envelop < ENVELOP_MIN)
envelop = ENVELOP_MIN;
value = value / sqrt_tab[(int)(envelop / 0.001)];
/* convert back from 0 DB level to sample value */
sample = (int)(value * ZERO_DB_LEVEL);
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
sample = -32768;
*samples++ = sample;
}
state->envelop_c = envelop;
}
void expand_audio(compander_t *state, int16_t *samples, int num)
{
int32_t sample;
double value, envelop, step_up, step_down;
int i;
step_up = state->step_up;
step_down = state->step_down;
envelop = state->envelop_e;
for (i = 0; i < num; i++) {
/* normalize sample value to 0 DB level */
value = (double)(*samples) / ZERO_DB_LEVEL;
if (fabs(value) > envelop)
envelop *= step_up;
else
envelop *= step_down;
if (envelop < ENVELOP_MIN)
envelop = ENVELOP_MIN;
value = value * envelop;
/* convert back from 0 DB level to sample value */
sample = (int)(value * ZERO_DB_LEVEL);
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
sample = -32768;
*samples++ = sample;
}
state->envelop_e = envelop;
}

@ -0,0 +1,11 @@
typedef struct compander {
double step_up;
double step_down;
double envelop_c;
double envelop_e;
} compander_t;
void init_compander(compander_t *state, int samplerate, double attack_ms, double recovery_ms);
void compress_audio(compander_t *state, int16_t *samples, int num);
void expand_audio(compander_t *state, int16_t *samples, int num);
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