absolute_value.h

/*
 * Copyright © 2024 Mark Adams
 *
 * This file is part of The Synthstrom Audible Deluge Firmware.
 *
 * The Synthstrom Audible Deluge Firmware 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 3 of the License, 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.
 * If not, see <https://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include "dsp/stereo_sample.h"
#include <cmath>
#include <span>
 
class AbsValueFollower {
public:
    AbsValueFollower() = default;
    void setup(q31_t attack, q31_t release);

    void reset() {
        meanL = 0;
        lastMeanL = 0;
        meanR = 0;
        lastMeanR = 0;
    }
 
    // attack/release in range 0 to 2^31
    inline q31_t getAttack() { return attackKnobPos; }
    inline int32_t getAttackMS() { return attackMS; }
    int32_t setAttack(q31_t attack) {
        // this exp will be between 1 and 7ish, half the knob range is about 2.5
        attackMS = 0.5 + (std::exp(2 * float(attack) / ONE_Q31f) - 1) * 10;
        a_ = (-1000.0 / kSampleRate) / attackMS;
        attackKnobPos = attack;
        return attackMS;
    };
 
    inline q31_t getRelease() { return releaseKnobPos; }
    inline int32_t getReleaseMS() { return releaseMS; }
    int32_t setRelease(q31_t release) {
        // this exp will be between 1 and 7ish, half the knob range is about 2.5
        releaseMS = 50 + (std::exp(2 * float(release) / ONE_Q31f) - 1) * 50;
        r_ = (-1000.0 / kSampleRate) / releaseMS;
        releaseKnobPos = release;
        return releaseMS;
    };
 
    StereoFloatSample calcApproxRMS(std::span<StereoSample> buffer);
 
private:
    float runEnvelope(float current, float desired, float numSamples);
    // for display
    float attackMS{1};
    float releaseMS{10};
    // parameters in use
    float a_ = (-1000.0f / kSampleRate) / attackMS;
 
    float r_ = (-1000.0f / kSampleRate) / releaseMS;
 
    // state
    float state{0};
    float rms{0};
    float meanL{0};
    float lastMeanL{0};
    float meanR{0};
    float lastMeanR{0};
 
    // raw knob positions
    q31_t attackKnobPos{0};
    q31_t releaseKnobPos{0};
};