Cepstral Pitch Tracker

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*

    This file is Copyright (c) 2012 Chris Cannam

    Permission is hereby granted, free of charge, to any person

    obtaining a copy of this software and associated documentation

    files (the "Software"), to deal in the Software without

    restriction, including without limitation the rights to use, copy,

    modify, merge, publish, distribute, sublicense, and/or sell copies

    of the Software, and to permit persons to whom the Software is

    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be

    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR

    ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF

    CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION

    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

*/

#include "PeakInterpolator.h"

#include <iostream>

static double 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

PeakInterpolator::findPeakLocation(const double *data, int size)

{

    double maxval;

    int maxidx = 0;

    int i;

    for (i = 0; i < size; ++i) {

        if (i == 0 || data[i] > maxval) {

            maxval = data[i];

            maxidx = i;

        }

    }

    return findPeakLocation(data, size, maxidx);

}

double

PeakInterpolator::findPeakLocation(const double *data, int size, int peakIndex)

{

    // after jos, 

    // https://ccrma.stanford.edu/~jos/sasp/Quadratic_Interpolation_Spectral_Peaks.html

    if (peakIndex < 1 || peakIndex > size - 2) {

        return peakIndex;

    }

    double alpha = data[peakIndex-1];

    double beta  = data[peakIndex];

    double gamma = data[peakIndex+1];

    double denom = (alpha - 2*beta + gamma);

    if (denom == 0) {

        // flat

        return peakIndex;

    }

    double p = ((alpha - gamma) / denom) / 2.0;

    return double(peakIndex) + p;

}