Fixing compander

pull/1/head
Andreas Eversberg 7 years ago
parent 9de121109d
commit 2a092b8cf7
  1. 1
      .gitignore
  2. 1
      configure.ac
  3. 2
      src/Makefile.am
  4. 113
      src/common/compander.c
  5. 20
      src/common/compander.h
  6. 19
      src/nmt/dsp.c
  7. 12
      src/test/Makefile.am
  8. 122
      src/test/test_compander.c

1
.gitignore vendored

@ -23,3 +23,4 @@ src/common/libcommon.a
src/anetz/anetz
src/bnetz/bnetz
src/nmt/nmt
test/test_compander

@ -32,6 +32,7 @@ AC_OUTPUT(
src/anetz/Makefile
src/bnetz/Makefile
src/nmt/Makefile
src/test/Makefile
src/Makefile
Makefile)

@ -1,3 +1,3 @@
AUTOMAKE_OPTIONS = foreign
SUBDIRS = common anetz bnetz nmt
SUBDIRS = common anetz bnetz nmt test

@ -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
peak *= step_down;
if (peak > envelope)
envelope *= step_up;
else
envelop *= step_down;
if (envelop < ENVELOP_MIN)
envelop = ENVELOP_MIN;
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;
}

@ -1,11 +1,21 @@
typedef struct compander {
double step_up;
double step_down;
double envelop_c;
double envelop_e;
struct {
double unaffected;
double step_up;
double step_down;
double peak;
double envelope;
} c;
struct {
double unaffected;
double step_up;
double step_down;
double peak;
double envelope;
} e;
} compander_t;
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);
void compress_audio(compander_t *state, int16_t *samples, int num);
void expand_audio(compander_t *state, int16_t *samples, int num);

@ -33,8 +33,9 @@
#define PI M_PI
/* signalling */
#define TX_PEAK_FSK 16384 /* peak amplitude of signalling FSK */
#define TX_PEAK_SUPER 1638 /* peak amplitude of supervisory signal */
#define TX_AUDIO_0dBm0 16384 /* works quite well */
#define TX_PEAK_FSK 16384.0 /* peak amplitude of signalling FSK */
#define TX_PEAK_SUPER 1638.0 /* peak amplitude of supervisory signal */
#define BIT_RATE 1200 /* baud rate */
#define STEPS_PER_BIT 10 /* step every 1/12000 sec */
#define DIALTONE_HZ 425.0 /* dial tone frequency */
@ -84,7 +85,7 @@ int dsp_init_sender(nmt_t *nmt)
int i;
/* attack (3ms) and recovery time (13.5ms) according to NMT specs */
init_compander(&nmt->cstate, 8000, 3.0, 13.5);
init_compander(&nmt->cstate, 8000, 3.0, 13.5, TX_AUDIO_0dBm0);
if ((nmt->sender.samplerate % (BIT_RATE * STEPS_PER_BIT))) {
PDEBUG(DDSP, DEBUG_ERROR, "Sample rate must be a multiple of %d bits per second.\n", BIT_RATE * STEPS_PER_BIT);
@ -238,7 +239,8 @@ static void fsk_receive_bit(nmt_t *nmt, int bit, double quality, double level)
/* send telegramm */
frames_elapsed = (double)(nmt->rx_sample_count_current - nmt->rx_sample_count_last) / (double)(nmt->samples_per_bit * 166);
nmt_receive_frame(nmt, nmt->fsk_filter_frame, nmt->fsk_filter_qualitysum / 140.0, nmt->fsk_filter_levelsum / 140.0, frames_elapsed);
/* convert level so that received level at TX_PEAK_FSK results in 1.0 (100%) */
nmt_receive_frame(nmt, nmt->fsk_filter_frame, nmt->fsk_filter_qualitysum / 140.0, nmt->fsk_filter_levelsum / 140.0 * 32768.0 / TX_PEAK_FSK, frames_elapsed);
}
char *show_level(int value)
@ -339,8 +341,8 @@ static void super_decode(nmt_t *nmt, int16_t *samples, int length)
#if 0
/* normalize levels */
result[0] *= 32768.0 / (double)TX_PEAK_SUPER / 0.63662;
result[1] *= 32768.0 / (double)TX_PEAK_SUPER / 0.63662;
result[0] *= 32768.0 / TX_PEAK_SUPER / 0.63662;
result[1] *= 32768.0 / TX_PEAK_SUPER / 0.63662;
printf("signal=%.4f noise=%.4f\n", result[0], result[1]);
#endif
@ -412,7 +414,7 @@ void sender_receive(sender_t *sender, int16_t *samples, int length)
spl = nmt->fsk_filter_spl;
for (i = 0; i < length; i++) {
#ifdef DEBUG_MODULATOR
printf("|%s|\n", show_level((int)((samples[i] / (double)TX_PEAK_FSK) * 50)+50));
printf("|%s|\n", show_level((int)((samples[i] / TX_PEAK_FSK) * 50)+50));
#endif
spl[pos++] = samples[i];
if (nmt->fsk_filter_mute) {
@ -441,7 +443,8 @@ void sender_receive(sender_t *sender, int16_t *samples, int length)
spl = nmt->sender.rxbuf;
pos = nmt->sender.rxbuf_pos;
for (i = 0; i < count; i++) {
spl[pos++] = down[i];
#warning hacking: remove after preemphasis implementation
spl[pos++] = down[i] / 2;
if (pos == 160) {
call_tx_audio(nmt->sender.callref, spl, 160);
pos = 0;

@ -0,0 +1,12 @@
AM_CPPFLAGS = -Wall -g $(all_includes)
noinst_PROGRAMS = \
test_compander
test_compander_SOURCES = test_compander.c
test_compander_LDADD = \
$(COMMON_LA) \
$(top_builddir)/src/common/libcommon.a \
-lm

@ -0,0 +1,122 @@
#include <stdio.h>
#include <stdint.h>
#include <math.h>
#include <string.h>
#include "../common/compander.h"
#define level2db(level) (20 * log10(level))
#define db2level(db) pow(10, (double)db / 20.0)
#define SAMPLERATE 48000
#define ATTACK_MS 15.0
#define RECOVERY_MS 15.0
#define UNAFFECTED 10000.0
static double test_frequency[3] = { 2000.0, 4000.0, 1000.0 };
static int16_t samples_4db[SAMPLERATE];
static int16_t samples_16db[SAMPLERATE];
static int16_t samples_2db[SAMPLERATE];
static int16_t samples_8db[SAMPLERATE];
static int16_t samples_0db[SAMPLERATE];
/* generate 2 samples: one with -4 dB, the other with -16 dB */
static void generate_test_sample(double test_frequency)
{
int i;
double value;
for (i = 0; i < SAMPLERATE; i++) {
value = cos(2.0 * M_PI * test_frequency / (double)SAMPLERATE * i);
samples_4db[i] = (int)(UNAFFECTED * value * db2level(-4));
samples_16db[i] = (int)(UNAFFECTED * value * db2level(-16));
samples_2db[i] = (int)(UNAFFECTED * value * db2level(-2));
samples_8db[i] = (int)(UNAFFECTED * value * db2level(-8));
samples_0db[i] = (int)(UNAFFECTED * value);
}
}
static void check_level(int16_t *samples, double duration, const char *desc, double target_db)
{
int i;
int last = 0, envelop = 0;
int up = 0;
double factor;
int when = (int)((double)SAMPLERATE + (double)SAMPLERATE * duration / 1000.0 + 0.5);
for (i = 0; i < when; i++) {
if (last < samples[i]) {
up = 1;
} else if (last > samples[i]) {
if (up) {
envelop = last;
}
up = 0;
}
#if 0
if (i >= (SAMPLERATE-(SAMPLERATE/100)) && (i % (SAMPLERATE/(SAMPLERATE/10))) == 0)
printf("%s: envelop = %.4f (when=%d)\n", desc, level2db((double)envelop / UNAFFECTED), i);
#endif
last = samples[i];
}
factor = (envelop / UNAFFECTED) / db2level(target_db);
printf("%s: envelop after the instance of %.1f ms is %.4f db factor =%.4f\n", desc, duration, level2db((double)envelop / UNAFFECTED), factor);
}
int main(void)
{
compander_t cstate;
int16_t samples[SAMPLERATE * 2];
int f;
init_compander(&cstate, SAMPLERATE, ATTACK_MS, RECOVERY_MS, UNAFFECTED);
for (f = 0; f < 3; f++) {
/* -16 and -4 dB */
generate_test_sample(test_frequency[f]);
/* low to high transition */
memcpy(samples, samples_16db, SAMPLERATE * 2);
memcpy(samples + SAMPLERATE, samples_4db, SAMPLERATE * 2);
compress_audio(&cstate, samples, SAMPLERATE * 2);
check_level(samples, ATTACK_MS, "compressor attack", -2.0);
/* high to low transition */
memcpy(samples, samples_4db, SAMPLERATE * 2);
memcpy(samples + SAMPLERATE, samples_16db, SAMPLERATE * 2);
compress_audio(&cstate, samples, SAMPLERATE * 2);
check_level(samples, RECOVERY_MS, "compressor recovery", -8.0);
/* low to high transition */
memcpy(samples, samples_8db, SAMPLERATE * 2);
memcpy(samples + SAMPLERATE, samples_2db, SAMPLERATE * 2);
expand_audio(&cstate, samples, SAMPLERATE * 2);
check_level(samples, ATTACK_MS, "expander attack", -4.0);
/* high to low transition */
memcpy(samples, samples_2db, SAMPLERATE * 2);
memcpy(samples + SAMPLERATE, samples_8db, SAMPLERATE * 2);
expand_audio(&cstate, samples, SAMPLERATE * 2);
check_level(samples, RECOVERY_MS, "expander recovery", -16.0);
/* 0 DB */
memcpy(samples, samples_0db, SAMPLERATE * 2);
memcpy(samples + SAMPLERATE, samples_0db, SAMPLERATE * 2);
check_level(samples, RECOVERY_MS, "unaffected level", 0.0);
puts("");
}
return 0;
}
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