Method extractAverageGroupDelay

src/internal/src/FFTFrame.cpp:155–203

}

double FFTFrame::extractAverageGroupDelay()
{
    float * realP = realData();
    float * imagP = imagData();

    double aveSum = 0.0;
    double weightSum = 0.0;
    double lastPhase = 0.0;

    int halfSize = fftSize() / 2;

    const double kSamplePhaseDelay = (2.0 * static_cast<double>(LAB_PI)) / double(fftSize());

    // Calculate weighted average group delay
    for (int i = 0; i < halfSize; i++)
    {
        Complex c(realP[i], imagP[i]);
        double mag = abs(c);
        double phase = arg(c);

        double deltaPhase = phase - lastPhase;
        lastPhase = phase;

        // Unwrap
        if (deltaPhase < -static_cast<double>(LAB_PI))
            deltaPhase += 2.0 * static_cast<double>(LAB_PI);
        if (deltaPhase > static_cast<double>(LAB_PI))
            deltaPhase -= 2.0 * static_cast<double>(LAB_PI);

        aveSum += mag * deltaPhase;
        weightSum += mag;
    }

    // Note how we invert the phase delta wrt frequency since this is how group delay is defined
    double ave = aveSum / weightSum;
    double aveSampleDelay = -ave / kSamplePhaseDelay;

    // Leave 20 sample headroom (for leading edge of impulse)
    if (aveSampleDelay > 20.0)
        aveSampleDelay -= 20.0;

    // Remove average group delay (minus 20 samples for headroom)
    addConstantGroupDelay(-aveSampleDelay);

    // Remove DC offset
    realP[0] = 0.0f;

    return aveSampleDelay;
}

void FFTFrame::addConstantGroupDelay(double sampleFrameDelay)
{