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Fixing compander

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This commit is contained in:
Andreas Eversberg
2016-04-23 14:33:02 +02:00
parent 9de121109d
commit 2a092b8cf7
8 changed files with 233 additions and 57 deletions
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113
src/common/compander.c
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@@ -17,42 +17,47 @@
* 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 "compander.h"
/* this is the 0 DB level that stays 0 DB after compression / espansion */
#define ZERO_DB_LEVEL 16384.0
//#define db2level(db) pow(10, (double)db / 20.0)
/* what factor shall the gain raise and fall after given attack/recovery time */
#define ATTACK_FACTOR 1.5
#define RECOVERY_FACTOR 0.75
/* factor is the gain (raise and fall) after given attack/recovery time */
#define COMPRESS_ATTACK_FACTOR 1.83 /* about 1.5 after 12 dB step up */
#define COMPRESS_RECOVERY_FACTOR 0.44 /* about 0.75 after 12 dB step down */
#define EXPAND_ATTACK_FACTOR 1.145 /* about 0.57 after 6 dB step up */
#define EXPAND_RECOVERY_FACTOR 0.753 /* about 1.51 after 6 dB step down */
/* Minimum level value to keep state */
#define ENVELOP_MIN 0.001
#define ENVELOPE_MIN 0.001
static double sqrt_tab[10000];
/*
* Generate companding tables according to NMT specification
* Init compander according to ITU-T G.162 specification
*
* Hopefully this is correct
*
*/
void init_compander(compander_t *state, int samplerate, double attack_ms, double recovery_ms)
void init_compander(compander_t *state, int samplerate, double attack_ms, double recovery_ms, int unaffected_level)
{
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);
state->c.peak = 1.0;
state->c.envelope = 1.0;
state->e.peak = 1.0;
state->e.envelope = 1.0;
state->c.step_up = pow(COMPRESS_ATTACK_FACTOR, 1000.0 / attack_ms / (double)samplerate);
state->c.step_down = pow(COMPRESS_RECOVERY_FACTOR, 1000.0 / recovery_ms / (double)samplerate);
state->e.step_up = pow(EXPAND_ATTACK_FACTOR, 1000.0 / attack_ms / (double)samplerate);
state->e.step_down = pow(EXPAND_RECOVERY_FACTOR, 1000.0 / recovery_ms / (double)samplerate);
state->c.unaffected = unaffected_level;
state->e.unaffected = unaffected_level;
// FIXME: make global, not at instance
for (i = 0; i < 10000; i++)
@@ -62,64 +67,85 @@ void init_compander(compander_t *state, int samplerate, double attack_ms, double
void compress_audio(compander_t *state, int16_t *samples, int num)
{
int32_t sample;
double value, envelop, step_up, step_down;
double value, peak, envelope, step_up, step_down, unaffected;
int i;
step_up = state->step_up;
step_down = state->step_down;
envelop = state->envelop_c;
step_up = state->c.step_up;
step_down = state->c.step_down;
peak = state->c.peak;
envelope = state->c.envelope;
unaffected = state->c.unaffected;
// printf("envelop=%.4f\n", envelop);
// printf("envelope=%.4f\n", envelope);
for (i = 0; i < num; i++) {
/* normalize sample value to 0 DB level */
value = (double)(*samples) / ZERO_DB_LEVEL;
/* normalize sample value to unaffected level */
value = (double)(*samples) / unaffected;
if (fabs(value) > envelop)
envelop *= step_up;
/* 'peak' is the level that raises directly with the signal
* level, but falls with specified recovery rate. */
if (fabs(value) > peak)
peak = fabs(value);
else
envelop *= step_down;
if (envelop < ENVELOP_MIN)
envelop = ENVELOP_MIN;
peak *= step_down;
/* 'evelope' is the level that raises with the specified attack
* rate to 'peak', but falls with specified recovery rate. */
if (peak > envelope)
envelope *= step_up;
else
envelope = peak;
if (envelope < ENVELOPE_MIN)
envelope = ENVELOPE_MIN;
value = value / sqrt_tab[(int)(envelop / 0.001)];
value = value / sqrt_tab[(int)(envelope / 0.001)];
//if (i > 47000.0 && i < 48144)
//printf("time=%.4f envelope=%.4fdb, value=%.4f\n", (double)i/48000.0, 20*log10(envelope), value);
/* convert back from 0 DB level to sample value */
sample = (int)(value * ZERO_DB_LEVEL);
sample = (int)(value * unaffected);
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
sample = -32768;
*samples++ = sample;
}
//exit(0);
state->envelop_c = envelop;
state->c.envelope = envelope;
state->c.peak = peak;
}
void expand_audio(compander_t *state, int16_t *samples, int num)
{
int32_t sample;
double value, envelop, step_up, step_down;
double value, peak, envelope, step_up, step_down, unaffected;
int i;
step_up = state->step_up;
step_down = state->step_down;
envelop = state->envelop_e;
step_up = state->e.step_up;
step_down = state->e.step_down;
peak = state->e.peak;
envelope = state->e.envelope;
unaffected = state->e.unaffected;
for (i = 0; i < num; i++) {
/* normalize sample value to 0 DB level */
value = (double)(*samples) / ZERO_DB_LEVEL;
value = (double)(*samples) / unaffected;
if (fabs(value) > envelop)
envelop *= step_up;
/* for comments: see compress_audio() */
if (fabs(value) > peak)
peak = fabs(value);
else
envelop *= step_down;
if (envelop < ENVELOP_MIN)
envelop = ENVELOP_MIN;
peak *= step_down;
if (peak > envelope)
envelope *= step_up;
else
envelope = peak;
if (envelope < ENVELOPE_MIN)
envelope = ENVELOPE_MIN;
value = value * envelop;
value = value * envelope;
/* convert back from 0 DB level to sample value */
sample = (int)(value * ZERO_DB_LEVEL);
sample = (int)(value * unaffected);
if (sample > 32767)
sample = 32767;
else if (sample < -32768)
@@ -127,6 +153,7 @@ void expand_audio(compander_t *state, int16_t *samples, int num)
*samples++ = sample;
}
state->envelop_e = envelop;
state->e.envelope = envelope;
state->e.peak = peak;
}