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 "compressor.h"
      23              : 
      24              : #include "audiomathutils.h"
      25              : 
      26              : #include "log.h"
      27              : 
      28              : using namespace muse::audio;
      29              : using namespace muse::audio::dsp;
      30              : 
      31              : static constexpr float RATIO = 4.f;
      32              : 
      33            0 : Compressor::Compressor(const unsigned int sampleRate)
      34            0 :     : m_filterConfig(sampleRate, RATIO),
      35            0 :     m_feedbackFactor(1.f)   // 0 = feed forward, 1 = feed back
      36              : {
      37            0 : }
      38              : 
      39            0 : bool Compressor::isActive() const
      40              : {
      41            0 :     return m_isActive;
      42              : }
      43              : 
      44            0 : void Compressor::setIsActive(const bool active)
      45              : {
      46            0 :     m_isActive = active;
      47            0 : }
      48              : 
      49            0 : volume_db_t Compressor::gainSmoothing(const float& newGainReduction) const
      50              : {
      51            0 :     float coefficient = 0.f;
      52              : 
      53            0 :     if (newGainReduction <= m_previousGainReduction) {
      54            0 :         coefficient = m_filterConfig.attackTimeCoefficient();
      55              :     } else {
      56            0 :         coefficient = m_filterConfig.releaseTimeCoefficient();
      57              :     }
      58              : 
      59            0 :     return (coefficient * m_previousGainReduction) + ((1 - coefficient) * newGainReduction);
      60              : }
      61              : 
      62            0 : volume_db_t Compressor::computeGain(const volume_db_t& logarithmSample) const
      63              : {
      64            0 :     if (logarithmSample < m_softThresholdLower) {
      65            0 :         return logarithmSample;
      66              :     }
      67              : 
      68            0 :     if (logarithmSample >= m_softThresholdLower && logarithmSample <= m_softThresholdUpper) {
      69              :         return logarithmSample
      70            0 :                + ((((1 / m_filterConfig.ratio()) - 1) * std::pow(logarithmSample - m_softThresholdUpper, 2))
      71            0 :                   / (2 * m_filterConfig.kneeWidth()));
      72              :     }
      73              : 
      74            0 :     return m_filterConfig.logarithmicThreshold()
      75            0 :            + ((logarithmSample - m_filterConfig.logarithmicThreshold()) / m_filterConfig.ratio());
      76              : }
      77              : 
      78            0 : void Compressor::process(const float linearRms, float* buffer, const audioch_t& audioChannelsCount, const samples_t samplesPerChannel)
      79              : {
      80            0 :     float dbGain = muse::linear_to_db(linearRms);
      81              : 
      82            0 :     if (dbGain <= m_filterConfig.minimumOperableLevel()) {
      83            0 :         return;
      84              :     }
      85              : 
      86              :     // trying to predict the next sample by the previous gain reduction
      87            0 :     dbGain += m_feedbackFactor * m_feedbackGain;
      88              : 
      89            0 :     float dbDiff = computeGain(dbGain) - dbGain;
      90              : 
      91            0 :     m_feedbackGain = dbDiff;
      92            0 :     float gainFact = muse::db_to_linear(dbDiff * (1.f + m_feedbackFactor));
      93              : 
      94            0 :     float currentGainReduction = std::min(gainFact, m_previousGainReduction);
      95              : 
      96              :     // apply gain
      97            0 :     for (audioch_t audioChNum = 0; audioChNum < audioChannelsCount; ++audioChNum) {
      98            0 :         multiplySamples(buffer, audioChannelsCount, audioChNum, samplesPerChannel, currentGainReduction);
      99              :     }
     100              : 
     101            0 :     m_previousGainReduction = currentGainReduction;
     102              : }