Method setLowShelfParams

src/internal/src/Biquad.cpp:172–210

}

void Biquad::setLowShelfParams(double frequency, double dbGain)
{
    // Clip frequencies to between 0 and 1, inclusive.
    frequency = std::max(0.0, std::min(frequency, 1.0));

    double A = pow(10.0, dbGain / 40);

    if (frequency == 1)
    {
        // The z-transform is a constant gain.
        setNormalizedCoefficients(A * A, 0, 0,
                                  1, 0, 0);
    }
    else if (frequency > 0)
    {
        double w0 = static_cast<double>(LAB_PI) * frequency;
        double S = 1;  // filter slope (1 is max value)
        double alpha = 0.5 * sin(w0) * sqrt((A + 1 / A) * (1 / S - 1) + 2);
        double k = cos(w0);
        double k2 = 2 * sqrt(A) * alpha;
        double aPlusOne = A + 1;
        double aMinusOne = A - 1;

        double b0 = A * (aPlusOne - aMinusOne * k + k2);
        double b1 = 2 * A * (aMinusOne - aPlusOne * k);
        double b2 = A * (aPlusOne - aMinusOne * k - k2);
        double a0 = aPlusOne + aMinusOne * k + k2;
        double a1 = -2 * (aMinusOne + aPlusOne * k);
        double a2 = aPlusOne + aMinusOne * k - k2;

        setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
    }
    else
    {
        // When frequency is 0, the z-transform is 1.
        setNormalizedCoefficients(1, 0, 0,
                                  1, 0, 0);
    }
}

void Biquad::setHighShelfParams(double frequency, double dbGain)
{