Method setAllpassParams

src/internal/src/Biquad.cpp:296–336

}

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

    // Don't let Q go negative, which causes an unstable filter.
    Q = std::max(0.0, Q);

    if (frequency > 0 && frequency < 1)
    {
        if (Q > 0)
        {
            double w0 = static_cast<double>(LAB_PI) * frequency;
            double alpha = sin(w0) / (2 * Q);
            double k = cos(w0);

            double b0 = 1 - alpha;
            double b1 = -2 * k;
            double b2 = 1 + alpha;
            double a0 = 1 + alpha;
            double a1 = -2 * k;
            double a2 = 1 - alpha;

            setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
        }
        else
        {
            // When Q = 0, the above formulas have problems. If we look at
            // the z-transform, we can see that the limit as Q->0 is -1, so
            // set the filter that way.
            setNormalizedCoefficients(-1, 0, 0,
                                      1, 0, 0);
        }
    }
    else
    {
        // When frequency is 0 or 1, the z-transform is 1.
        setNormalizedCoefficients(1, 0, 0,
                                  1, 0, 0);
    }
}

void Biquad::setNotchParams(double frequency, double Q)
{