Method interpolateFrequencyComponents

src/internal/src/FFTFrame.cpp:49–153

}

void FFTFrame::interpolateFrequencyComponents(const FFTFrame & frame1, const FFTFrame & frame2, double interp)
{
    // FIXME : with some work, this method could be optimized

    float * realP = realData();
    float * imagP = imagData();

    const float * realP1 = frame1.realData();
    const float * imagP1 = frame1.imagData();
    const float * realP2 = frame2.realData();
    const float * imagP2 = frame2.imagData();

    m_FFTSize = frame1.fftSize();
    m_log2FFTSize = frame1.log2FFTSize();

    double s1base = (1.0 - interp);
    double s2base = interp;

    double phaseAccum = 0.0;
    double lastPhase1 = 0.0;
    double lastPhase2 = 0.0;

    realP[0] = static_cast<float>(s1base * realP1[0] + s2base * realP2[0]);
    imagP[0] = static_cast<float>(s1base * imagP1[0] + s2base * imagP2[0]);

    int n = m_FFTSize / 2;

    for (int i = 1; i < n; ++i)
    {
        Complex c1(realP1[i], imagP1[i]);
        Complex c2(realP2[i], imagP2[i]);

        double mag1 = abs(c1);
        double mag2 = abs(c2);

        // Interpolate magnitudes in decibels
        double mag1db = 20.0 * log10(mag1);
        double mag2db = 20.0 * log10(mag2);

        double s1 = s1base;
        double s2 = s2base;

        double magdbdiff = mag1db - mag2db;

        // Empirical tweak to retain higher-frequency zeroes
        double threshold = (i > 16) ? 5.0 : 2.0;

        if (magdbdiff < -threshold && mag1db < 0.0)
        {
            s1 = pow(s1, 0.75);
            s2 = 1.0 - s1;
        }
        else if (magdbdiff > threshold && mag2db < 0.0)
        {
            s2 = pow(s2, 0.75);
            s1 = 1.0 - s2;
        }