Method updatePIController

src/fl/audio/auto_gain.cpp.hpp:159–197

}

float AutoGain::updatePIController(float targetGain, float dt) {
    const float error = targetGain - mLastGain;

    // Bug 4 fix: Use absolute error threshold when gain is small to avoid
    // huge errorRatio from dividing by tiny mLastGain
    const bool largeError = (mLastGain > 0.1f)
        ? (fl::abs(error) / mLastGain > 0.2f)  // Relative: >20% of current gain
        : (fl::abs(error) > 0.1f);              // Absolute: >0.1 when gain is tiny
    const float tau = largeError ? mGainFollowFastTau : mGainFollowSlowTau;

    // Proportional term
    const float pTerm = mKp * error;

    // Bug 1 fix: PI target is where we WANT gain to be (not mLastGain + delta + delta)
    // targetGain + pTerm + integrator = the desired gain level
    const float piTarget = targetGain + pTerm + mIntegrator;

    // Smooth with exponential filter using adaptive tau
    float alpha = 1.0f;
    if (tau > 0.0f && dt > 0.0f) {
        alpha = 1.0f - fl::exp(-dt / tau);
    }

    const float unclamped = mLastGain + alpha * (piTarget - mLastGain);

    // Bug 2 fix: Back-calculation anti-windup — only accumulate integrator
    // when output is NOT clamped. Decay integrator when saturated (WLED: *= 0.91)
    const bool saturated = (unclamped > mConfig.maxGain) || (unclamped < mConfig.minGain);
    if (saturated) {
        mIntegrator *= 0.91f;
    } else {
        mIntegrator += mKi * error * dt;
    }
    // Clamp integrator magnitude to prevent runaway in pathological cases
    const float maxIntegral = 4.0f * mConfig.maxGain;
    mIntegrator = fl::max(-maxIntegral, fl::min(maxIntegral, mIntegrator));

    return unclamped;
}

void AutoGain::applyGain(const vector<i16>& input, float gain, vector<i16>& output) {
    output.clear();