116 lines
3.9 KiB
C
116 lines
3.9 KiB
C
/* Sendevolumenregler to be used by B-Netz
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*
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* (C) 2017 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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*/
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/* This function keeps the speech level for the transmitter constant.
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*
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* B-Netz specs say that levels are amplified to speech level. The maximum gain
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* is 16 dB. The level may overshoot by 2.6 dB and must lowered to normal level
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* within 20 ms. The level should raise 4.3 dB per second until target level is
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* reached.
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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 "../libsample/sample.h"
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#include "sendevolumenregler.h"
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#define db2level(db) pow(10, (double)db / 20.0)
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/*
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* Init function
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*
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* abwaerts_dbs = how many dB per second to lower the amplification, if input signal is above db0
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* aufwaerts_dbs = how many dB per second to raise the amplification, if input signal is below db0
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* maximum_db = limit of the output level above db0
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* minimum_db = below this input level, the amplification is not raised, so it stays constant.
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* db0_level = target level to be treated as 0 dB
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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_sendevolumenregler(sendevolumenregler_t *state, double samplerate, double abwaerts_dbs, double aufwaerts_dbs, double maximum_db, double minimum_db, double db0_level)
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{
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memset(state, 0, sizeof(*state));
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state->peak = 1.0;
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state->envelope = 1.0;
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state->db0_level = db0_level;
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state->step_down = pow(db2level(abwaerts_dbs), 1.0 / samplerate);
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state->step_up = pow(db2level(aufwaerts_dbs), 1.0 / samplerate);
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state->maximum_level = db2level(maximum_db);
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state->minimum_level = db2level(minimum_db);
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}
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/*
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* how to works:
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*
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* if value is above 'peak', raise 'peak' to value instantaniously
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* if value is below 'peak', lower 'peak' by 'step_up' (increase level)
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* if 'peak' is above 'envelope', raise 'envelope' by 'step_down' (decrease level)
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* if 'peak' is below 'envelope', lower 'envelope' to 'peak' (increase level)
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* 'envelope' will not fall below 'minimum_level' (maximum amplification)
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* if 'peak' is 'maximum_level' above 'envelope', raise 'envelope' to 'maximum_level' below 'peak'
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*/
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void sendevolumenregler(sendevolumenregler_t *state, sample_t *samples, int num)
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{
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double value, peak, envelope, step_up, step_down, maximum_level, minimum_level, db0_level;
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int i;
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db0_level = state->db0_level;
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step_up = state->step_up;
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step_down = state->step_down;
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maximum_level = state->maximum_level;
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minimum_level = state->minimum_level;
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peak = state->peak;
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envelope = state->envelope;
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for (i = 0; i < num; i++) {
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/* normalize sample value to db0_level level */
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value = *samples / db0_level;
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/* 'peak' is the level that raises directly with the value
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* level, but falls as specified by step_up. */
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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_up;
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/* 'evelope' is the level that raises with the specified step_down
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* to 'peak', but falls with 'peak'. */
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if (peak > envelope)
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envelope *= step_down;
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else
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envelope = peak;
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/* no envelope below minimum level */
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if (envelope < minimum_level)
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envelope = minimum_level;
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/* raise envelope, if 'peak' exceeds maximum level */
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if (peak / envelope > maximum_level)
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envelope = peak / maximum_level;
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*samples++ = value / envelope * db0_level;
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}
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state->envelope = envelope;
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state->peak = peak;
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}
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