vactrol.hpp

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#pragma once

 
#include <pulp/signal/denormal.hpp>
 
#include <algorithm>
#include <cmath>
 
namespace pulp::signal {

template <typename SampleType = float>
class VactrolConditionerT {
public:
    static constexpr double kMinRiseMs = 0.1;
    static constexpr double kMaxRiseMs = 50.0;
    static constexpr double kDefaultRiseMs = 2.0;

    static constexpr double kMinFallMs = 10.0;
    static constexpr double kMaxFallMs = 2000.0;
    static constexpr double kDefaultFallMs = 200.0;
 
    VactrolConditionerT() { update(); }
 
    void prepare(double sample_rate) {
        sample_rate_ = sample_rate > 0.0 ? sample_rate : sample_rate_;
        update();
    }
 
    void set_rise_ms(double ms) {
        rise_ms_ = std::clamp(ms, kMinRiseMs, kMaxRiseMs);
        update();
    }
 
    void set_fall_ms(double ms) {
        fall_ms_ = std::clamp(ms, kMinFallMs, kMaxFallMs);
        update();
    }
 
    double rise_ms() const { return rise_ms_; }
    double fall_ms() const { return fall_ms_; }
 
    void reset() { control_ = 0.0; }

    double control() const { return control_; }

    double process(double target) {
        // Do not admit a non-finite control into the recursive photoresistor
        // state: std::clamp intentionally passes NaN through because every
        // comparison is false. Resetting makes the following finite sample
        // recover deterministically instead of keeping NaN forever.
        if (!std::isfinite(target)) {
            reset();
            return 0.0;
        }
        const double clamped = std::clamp(target, 0.0, 1.0);
        const double coefficient = clamped > control_ ? rise_a_ : fall_a_;
        control_ = snap_to_zero(control_ + coefficient * (clamped - control_));
        return control_;
    }
 
private:
    void update() {
        // The `max` guards a zero-or-negative sample rate; the time floor above
        // already guards the ms side. Deliberately spelled out rather than
        // routed through `units::ms_to_onepole_coef` so that this stays
        // bit-identical to the coefficient `LowpassGateT` has always used.
        rise_a_ = 1.0 - std::exp(-1.0 / std::max(0.001 * rise_ms_ * sample_rate_, 1e-9));
        fall_a_ = 1.0 - std::exp(-1.0 / std::max(0.001 * fall_ms_ * sample_rate_, 1e-9));
    }
 
    double sample_rate_ = 44100.0;
    double rise_ms_ = kDefaultRiseMs;
    double fall_ms_ = kDefaultFallMs;
    double rise_a_ = 0.0;
    double fall_a_ = 0.0;
    double control_ = 0.0;
};
 
using VactrolConditioner = VactrolConditionerT<float>;
using VactrolConditioner64 = VactrolConditionerT<double>;
 
}  // namespace pulp::signal