Line data    Source code

       1              : /*
       2              :  * SPDX-License-Identifier: GPL-3.0-only
       3              :  * MuseScore-CLA-applies
       4              :  *
       5              :  * MuseScore Studio
       6              :  * Music Composition & Notation
       7              :  *
       8              :  * Copyright (C) 2021 MuseScore Limited and others
       9              :  *
      10              :  * This program is free software: you can redistribute it and/or modify
      11              :  * it under the terms of the GNU General Public License version 3 as
      12              :  * published by the Free Software Foundation.
      13              :  *
      14              :  * This program is distributed in the hope that it will be useful,
      15              :  * but WITHOUT ANY WARRANTY; without even the implied warranty of
      16              :  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      17              :  * GNU General Public License for more details.
      18              :  *
      19              :  * You should have received a copy of the GNU General Public License
      20              :  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
      21              :  */
      22              : #include "limiter.h"
      23              : 
      24              : #include "audiomathutils.h"
      25              : 
      26              : using namespace muse::audio;
      27              : using namespace muse::audio::dsp;
      28              : 
      29              : static constexpr volume_db_t THRESHOLD = volume_dbfs_t::make(0.f);
      30              : 
      31            0 : Limiter::Limiter(const unsigned int sampleRate)
      32            0 :     : m_filterConfig(sampleRate, 1.f, THRESHOLD)
      33              : {
      34            0 : }
      35              : 
      36            0 : bool Limiter::isActive() const
      37              : {
      38            0 :     return m_isActive;
      39              : }
      40              : 
      41            0 : void Limiter::setIsActive(const bool active)
      42              : {
      43            0 :     m_isActive = active;
      44            0 : }
      45              : 
      46            0 : volume_db_t Limiter::gainSmoothing(const float newGainReduction) const
      47              : {
      48            0 :     float coefficient = 0.f;
      49              : 
      50            0 :     if (newGainReduction <= m_previousGainReduction) {
      51            0 :         coefficient = m_filterConfig.attackTimeCoefficient();
      52              :     } else {
      53            0 :         coefficient = m_filterConfig.releaseTimeCoefficient();
      54              :     }
      55              : 
      56            0 :     return (coefficient * m_previousGainReduction) + ((1 - coefficient) * newGainReduction);
      57              : }
      58              : 
      59            0 : volume_db_t Limiter::computeGain(const volume_db_t& logarithmSample) const
      60              : {
      61            0 :     if (logarithmSample < m_filterConfig.softThresholdLower()) {
      62            0 :         return logarithmSample;
      63              :     }
      64              : 
      65            0 :     if (logarithmSample >= m_filterConfig.softThresholdLower() && logarithmSample <= m_filterConfig.softThresholdUpper()) {
      66              :         return logarithmSample
      67            0 :                - (std::pow((logarithmSample - m_filterConfig.softThresholdUpper()), 2)
      68            0 :                   / (2 * m_filterConfig.kneeWidth()));
      69              :     }
      70              : 
      71            0 :     return m_filterConfig.logarithmicThreshold();
      72              : }
      73              : 
      74            0 : void Limiter::process(const float& linearRms, float* buffer, const audioch_t& audioChannelsCount,
      75              :                       const samples_t samplesPerChannel)
      76              : {
      77            0 :     volume_db_t rmsDb = muse::linear_to_db(linearRms);
      78              : 
      79            0 :     if (rmsDb <= m_filterConfig.minimumOperableLevel()) {
      80            0 :         return;
      81              :     }
      82              : 
      83              :     // gain computing
      84            0 :     float computedGain = computeGain(rmsDb) - rmsDb;
      85              : 
      86              :     // gain smoothing
      87            0 :     float smoothedGain = gainSmoothing(computedGain);
      88            0 :     m_previousGainReduction = smoothedGain;
      89              : 
      90              :     // gain make-up
      91            0 :     float makeUpGain = smoothedGain + m_filterConfig.makeUpGain();
      92              : 
      93              :     // total linear gain
      94            0 :     float totalLinearGain = muse::db_to_linear(makeUpGain);
      95              : 
      96              :     // apply linear gain
      97            0 :     for (audioch_t audioChNum = 0; audioChNum < audioChannelsCount; ++audioChNum) {
      98            0 :         multiplySamples(buffer, audioChannelsCount, audioChNum, samplesPerChannel, totalLinearGain);
      99              :     }
     100              : }