152 lines
4.4 KiB
C
152 lines
4.4 KiB
C
/* Compandor to use various networks like C-Netz / NMT / AMPS / TACS
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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 "../common/sample.h"
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#include "compandor.h"
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//#define db2level(db) pow(10, (double)db / 20.0)
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/* factor is the gain (raise and fall) after given attack/recovery time */
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#define COMPRESS_ATTACK_FACTOR 1.83 /* about 1.5 after 12 dB step up */
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#define COMPRESS_RECOVERY_FACTOR 0.44 /* about 0.75 after 12 dB step down */
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#define EXPAND_ATTACK_FACTOR 1.145 /* about 0.57 after 6 dB step up */
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#define EXPAND_RECOVERY_FACTOR 0.753 /* about 1.51 after 6 dB step down */
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/* Minimum level value to keep state */
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#define ENVELOPE_MIN 0.001
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/* Maximum level, to prevent sqrt_tab to overflow */
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#define ENVELOPE_MAX 9.990
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static double sqrt_tab[10000];
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/*
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* Init compandor according to ITU-T G.162 specification
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*
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* Hopefully this is correct
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*
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*/
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void init_compandor(compandor_t *state, double samplerate, double attack_ms, double recovery_ms, double unaffected_level)
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{
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int i;
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memset(state, 0, sizeof(*state));
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state->c.peak = 1.0;
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state->c.envelope = 1.0;
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state->e.peak = 1.0;
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state->e.envelope = 1.0;
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state->c.step_up = pow(COMPRESS_ATTACK_FACTOR, 1000.0 / attack_ms / samplerate);
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state->c.step_down = pow(COMPRESS_RECOVERY_FACTOR, 1000.0 / recovery_ms / samplerate);
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state->e.step_up = pow(EXPAND_ATTACK_FACTOR, 1000.0 / attack_ms / samplerate);
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state->e.step_down = pow(EXPAND_RECOVERY_FACTOR, 1000.0 / recovery_ms / samplerate);
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state->c.unaffected = unaffected_level;
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state->e.unaffected = unaffected_level;
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// FIXME: make global, not at instance
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for (i = 0; i < 10000; i++)
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sqrt_tab[i] = sqrt(i * 0.001);
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}
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void compress_audio(compandor_t *state, sample_t *samples, int num)
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{
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double value, peak, envelope, step_up, step_down, unaffected;
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int i;
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step_up = state->c.step_up;
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step_down = state->c.step_down;
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peak = state->c.peak;
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envelope = state->c.envelope;
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unaffected = state->c.unaffected;
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// printf("envelope=%.4f\n", envelope);
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for (i = 0; i < num; i++) {
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/* normalize sample value to unaffected level */
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value = *samples / unaffected;
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/* 'peak' is the level that raises directly with the signal
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* level, but falls with specified recovery rate. */
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if (fabs(value) > peak)
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peak = fabs(value);
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else
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peak *= step_down;
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/* 'evelope' is the level that raises with the specified attack
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* rate to 'peak', but falls with specified recovery rate. */
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if (peak > envelope)
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envelope *= step_up;
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else
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envelope = peak;
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if (envelope < ENVELOPE_MIN)
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envelope = ENVELOPE_MIN;
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if (envelope > ENVELOPE_MAX)
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envelope = ENVELOPE_MAX;
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value = value / sqrt_tab[(int)(envelope / 0.001)];
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//if (i > 47000.0 && i < 48144)
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//printf("time=%.4f envelope=%.4fdb, value=%.4f\n", (double)i/48000.0, 20*log10(envelope), value);
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*samples++ = value * unaffected;
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}
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//exit(0);
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state->c.envelope = envelope;
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state->c.peak = peak;
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}
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void expand_audio(compandor_t *state, sample_t *samples, int num)
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{
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double value, peak, envelope, step_up, step_down, unaffected;
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int i;
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step_up = state->e.step_up;
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step_down = state->e.step_down;
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peak = state->e.peak;
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envelope = state->e.envelope;
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unaffected = state->e.unaffected;
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for (i = 0; i < num; i++) {
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/* normalize sample value to 0 DB level */
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value = *samples / unaffected;
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/* for comments: see compress_audio() */
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if (fabs(value) > peak)
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peak = fabs(value);
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else
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peak *= step_down;
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if (peak > envelope)
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envelope *= step_up;
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else
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envelope = peak;
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if (envelope < ENVELOPE_MIN)
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envelope = ENVELOPE_MIN;
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value = value * envelope;
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*samples++ = value * unaffected;
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}
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state->e.envelope = envelope;
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state->e.peak = peak;
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}
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