Cepstral Pitch Tracker

    m_vflen(1),

double

CepstrumPitchTracker::cubicInterpolate(const double y[4], double x)

{

    double a0 = y[3] - y[2] - y[0] + y[1];

    double a1 = y[0] - y[1] - a0;

    double a2 = y[2] - y[0];

    double a3 = y[1];

    return

        a0 * x * x * x +

        a1 * x * x +

        a2 * x +

        a3;

}

double

CepstrumPitchTracker::findInterpolatedPeak(const double *in, int maxbin)

{

    if (maxbin < 2 || maxbin > m_bins - 3) {

        return maxbin;

    }

    double maxval = 0.0;

    double maxidx = maxbin;

    const int divisions = 10;

    double y[4];

    y[0] = in[maxbin-1];

    y[1] = in[maxbin];

    y[2] = in[maxbin+1];

    y[3] = in[maxbin+2];

    for (int i = 0; i < divisions; ++i) {

        double probe = double(i) / double(divisions);

        double value = cubicInterpolate(y, probe);

        if (value > maxval) {

            maxval = value; 

            maxidx = maxbin + probe;

        }

    }

    y[3] = y[2];

    y[2] = y[1];

    y[1] = y[0];

    y[0] = in[maxbin-2];

    for (int i = 0; i < divisions; ++i) {

        double probe = double(i) / double(divisions);

        double value = cubicInterpolate(y, probe);

        if (value > maxval) {

            maxval = value; 

            maxidx = maxbin - 1 + probe;

        }

    }

/*

    std::cerr << "centre = " << maxbin << ": ["

              << in[maxbin-2] << ","

              << in[maxbin-1] << ","

              << in[maxbin] << ","

              << in[maxbin+1] << ","

              << in[maxbin+2] << "] -> " << maxidx << std::endl;

*/

    return maxidx;

}

    double cimax = findInterpolatedPeak(data, maxbin);

    double peakfreq = m_inputSampleRate / (cimax + m_binFrom);