Method setLowpassParams

src/internal/src/Biquad.cpp:77–116

}

void Biquad::setLowpassParams(double cutoff, double resonance)
{
    // Limit cutoff to 0 to 1.
    cutoff = std::max(0.0, std::min(cutoff, 1.0));

    if (cutoff == 1)
    {
        // When cutoff is 1, the z-transform is 1.
        setNormalizedCoefficients(1, 0, 0,
                                  1, 0, 0);
    }
    else if (cutoff > 0)
    {
        // Compute biquad coefficients for lowpass filter
        resonance = std::max(0.0, resonance);  // can't go negative
        double g = pow(10.0, 0.05 * resonance);
        double d = sqrt((4 - sqrt(16 - 16 / (g * g))) / 2);

        double theta = static_cast<double>(LAB_PI) * cutoff;
        double sn = 0.5 * d * sin(theta);
        double beta = 0.5 * (1 - sn) / (1 + sn);
        double gamma = (0.5 + beta) * cos(theta);
        double alpha = 0.25 * (0.5 + beta - gamma);

        double b0 = 2 * alpha;
        double b1 = 2 * 2 * alpha;
        double b2 = 2 * alpha;
        double a1 = 2 * -gamma;
        double a2 = 2 * beta;

        setNormalizedCoefficients(b0, b1, b2, 1, a1, a2);
    }
    else
    {
        // When cutoff is zero, nothing gets through the filter, so set
        // coefficients up correctly.
        setNormalizedCoefficients(0, 0, 0,
                                  1, 0, 0);
    }
}

void Biquad::setHighpassParams(double cutoff, double resonance)
{