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Add library to normalize speech level (Sendevolumenregler SVoR)

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Andreas Eversberg
2017-11-18 12:54:12 +01:00
parent 021c695883
commit 06092e90ed
8 changed files with 252 additions and 0 deletions
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115
src/libsendevolumenregler/sendevolumenregler.c Normal file
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/* Sendevolumenregler to be used by B-Netz
*
* (C) 2017 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/>.
*
*/
/* This function keeps the speech level for the transmitter constant.
*
* B-Netz specs say that levels are amplified to speech level. The maximum gain
* is 16 dB. The level may overshoot by 2.6 dB and must lowered to normal level
* within 20 ms. The level should raise 4.3 dB per second until target level is
* reached.
*/
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include "../libsample/sample.h"
#include "sendevolumenregler.h"
#define db2level(db) pow(10, (double)db / 20.0)
/*
* Init function
*
* abwaerts_dbs = how many dB per second to lower the amplification, if input signal is above dBm0
* aufwaerts_dbs = how many dB per second to raise the amplification, if input signal is below dBm0
* maximum_db = limit of the output level above dBm0
* minimum_db = below this input level, the amplification is not raised, so it stays constant.
* dbm0_level = target level to be treated as 0 dB
*
* Hopefully this is correct
*
*/
void init_sendevolumenregler(sendevolumenregler_t *state, double samplerate, double abwaerts_dbs, double aufwaerts_dbs, double maximum_db, double minimum_db, double dbm0_level)
{
memset(state, 0, sizeof(*state));
state->peak = 1.0;
state->envelope = 1.0;
state->dbm0_level = dbm0_level;
state->step_down = pow(db2level(abwaerts_dbs), 1.0 / samplerate);
state->step_up = pow(db2level(aufwaerts_dbs), 1.0 / samplerate);
state->maximum_level = db2level(maximum_db);
state->minimum_level = db2level(minimum_db);
}
/*
* how to works:
*
* if value is above 'peak', raise 'peak' to value instantaniously
* if value is below 'peak', lower 'peak' by 'step_up' (increase level)
* if 'peak' is above 'envelope', raise 'envelope' by 'step_down' (decrease level)
* if 'peak' is below 'envelope', lower 'envelope' to 'peak' (increase level)
* 'envelope' will not fall below 'minimum_level' (maximum amplification)
* if 'peak' is 'maximum_level' above 'envelope', raise 'envelope' to 'maximum_level' below 'peak'
*/
void sendevolumenregler(sendevolumenregler_t *state, sample_t *samples, int num)
{
double value, peak, envelope, step_up, step_down, maximum_level, minimum_level, dbm0_level;
int i;
dbm0_level = state->dbm0_level;
step_up = state->step_up;
step_down = state->step_down;
maximum_level = state->maximum_level;
minimum_level = state->minimum_level;
peak = state->peak;
envelope = state->envelope;
for (i = 0; i < num; i++) {
/* normalize sample value to dbm0_level level */
value = *samples / dbm0_level;
/* 'peak' is the level that raises directly with the value
* level, but falls as specified by step_up. */
if (fabs(value) > peak)
peak = fabs(value);
else
peak /= step_up;
/* 'evelope' is the level that raises with the specified step_down
* to 'peak', but falls with 'peak'. */
if (peak > envelope)
envelope *= step_down;
else
envelope = peak;
/* no envelope below minimum level */
if (envelope < minimum_level)
envelope = minimum_level;
/* raise envelope, if 'peak' exceeds maximum level */
if (peak / envelope > maximum_level)
envelope = peak / maximum_level;
*samples++ = value / envelope * dbm0_level;
}
state->envelope = envelope;
state->peak = peak;
}