auto_gain.h

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#pragma once
 
#include "fl/math/filter/filter.h"
#include "fl/stl/int.h"
#include "fl/stl/vector.h"
#include "fl/stl/noexcept.h"
 
namespace fl {
namespace audio {

enum class AGCPreset {
    AGCPreset_Normal, 
    AGCPreset_Vivid,  
    AGCPreset_Lazy,   
    AGCPreset_Custom  
};

struct AutoGainConfig {
    bool enabled = true;

    float minGain = 1.0f / 64.0f;

    float maxGain = 32.0f;

    float targetRMSLevel = 8000.0f;

    AGCPreset preset = AGCPreset::AGCPreset_Normal;
 
    // --- Custom PI tuning (only used when preset == AGCPreset_Custom) ---

    float peakDecayTau = 3.3f;

    float kp = 0.6f;

    float ki = 1.7f;

    float gainFollowSlowTau = 12.3f;

    float gainFollowFastTau = 0.38f;
};

class AutoGain {
public:
    AutoGain() FL_NO_EXCEPT;
    explicit AutoGain(const AutoGainConfig& config) FL_NO_EXCEPT;
    ~AutoGain() FL_NO_EXCEPT;

    void configure(const AutoGainConfig& config) FL_NO_EXCEPT;

    Sample process(const Sample& sample) FL_NO_EXCEPT;

    void reset() FL_NO_EXCEPT;

    struct Stats {
        float currentGain = 1.0f;           // Current gain multiplier
        float peakEnvelope = 0.0f;          // Current peak envelope estimate
        float targetGain = 1.0f;            // Target gain from PI controller
        float integrator = 0.0f;            // PI integrator state
        float inputRMS = 0.0f;              // Most recent input RMS
        float outputRMS = 0.0f;             // Most recent output RMS
        u32 samplesProcessed = 0;           // Total samples processed
    };
 
    const Stats& getStats() const FL_NO_EXCEPT { return mStats; }

    float getGain() const FL_NO_EXCEPT { return mStats.currentGain; }

    void setSampleRate(int sampleRate) FL_NO_EXCEPT { mSampleRate = sampleRate; }
 
private:
    void resolvePreset() FL_NO_EXCEPT;

    float computeTargetGain() FL_NO_EXCEPT;

    float updatePIController(float targetGain, float dt) FL_NO_EXCEPT;

    void applyGain(const vector<i16>& input, float gain, vector<i16>& output) FL_NO_EXCEPT;
 
    AutoGainConfig mConfig;
    Stats mStats;
    int mSampleRate = 44100;
 
    // Resolved preset parameters (populated by resolvePreset())
    float mPeakDecayTau = 3.3f;
    float mKp = 0.6f;
    float mKi = 1.7f;
    float mGainFollowSlowTau = 12.3f;
    float mGainFollowFastTau = 0.38f;

    AttackDecayFilter<float> mPeakEnvelope{0.01f, 3.3f, 0.0f};

    float mIntegrator = 0.0f;

    float mLastGain = 1.0f;

    vector<i16> mOutputBuffer;
};
 
} // namespace audio
} // namespace fl