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