Method setBandpassParams

src/internal/src/Biquad.cpp:380–424

}

void Biquad::setBandpassParams(double frequency, double Q)
{
    // No negative frequencies allowed.
    frequency = std::max(0.0, frequency);

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

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

            double b0 = alpha;
            double b1 = 0;
            double b2 = -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 the cutoff is zero, the z-transform approaches 0, if Q
        // > 0. When both Q and cutoff are zero, the z-transform is
        // pretty much undefined. What should we do in this case?
        // For now, just make the filter 0. When the cutoff is 1, the
        // z-transform also approaches 0.
        setNormalizedCoefficients(0, 0, 0,
                                  1, 0, 0);
    }
}

void Biquad::setZeroPolePairs(const complex<double> & zero, const complex<double> & pole)
{