103 lines
2.6 KiB
C++
103 lines
2.6 KiB
C++
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/*
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* Copyright (C) 2016 Jared Boone, ShareBrained Technology, Inc.
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*
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* This file is part of PortaPack.
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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 2, or (at your option)
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* 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; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifndef __AUDIO_COMPRESSOR_H__
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#define __AUDIO_COMPRESSOR_H__
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#include "dsp_types.hpp"
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#include "utility.hpp"
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#include <cmath>
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/* Code based on article in Journal of the Audio Engineering Society
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* Vol. 60, No. 6, 2012 June, by Dimitrios Giannoulis, Michael Massberg,
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* Joshua D. Reiss "Digital Dynamic Range Compressor Design – A Tutorial
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* and Analysis"
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*/
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class GainComputer {
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public:
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constexpr GainComputer(
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float ratio,
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float threshold
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) : ratio { ratio },
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slope { 1.0f / ratio - 1.0f },
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threshold_db { threshold }
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{
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}
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float operator()(const float x) const;
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private:
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const float ratio;
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const float slope;
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const float threshold_db;
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static constexpr float knee_width_db = 0.0f;
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static constexpr float db_floor = -120.0f;
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static constexpr float lin_floor = std::pow(10.0f, db_floor / 20.0f);
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static constexpr float log2_db_k = 20.0f * std::log10(2.0f);
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};
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class PeakDetectorBranchingSmooth {
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public:
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constexpr PeakDetectorBranchingSmooth(
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float att_a,
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float rel_a
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) : att_a { att_a },
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rel_a { rel_a }
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{
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}
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float operator()(const float db) {
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const auto a = (db > state) ? att_a : rel_a;
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state = db + a * (state - db);
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return state;
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}
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private:
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float state { 0.0f };
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const float att_a;
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const float rel_a;
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};
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class FeedForwardCompressor {
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public:
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void execute_in_place(const buffer_f32_t& buffer);
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private:
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static constexpr float fs = 12000.0f;
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static constexpr float ratio = 10.0f;
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static constexpr float threshold = -30.0f;
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GainComputer gain_computer { ratio, threshold };
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PeakDetectorBranchingSmooth peak_detector { tau_alpha(0.010f, fs), tau_alpha(0.300f, fs) };
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float execute_once(const float x);
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static constexpr float tau_alpha(const float tau, const float fs) {
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return std::exp(-1.0f / (tau * fs));
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}
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};
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#endif/*__AUDIO_COMPRESSOR_H__*/
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