/*
 *  Copyright 2006-2007 Columbia University.
 *
 *  This file is part of MEAPsoft.
 *
 *  MEAPsoft is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 *
 *  MEAPsoft is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with MEAPsoft; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 *  02110-1301 USA
 *
 *  See the file "COPYING" for the text of the license.
 */

package com.meapsoft.featextractors;

import com.meapsoft.STFT;

/**
 * A simple feature calculation that averages the spectral centroid of
 * all spectral frames in a given chunk.
 *
 * @author Ron Weiss (ronw@ee.columbia.edu)
 */

public class AvgSpecCentroid extends FeatureExtractor 
{
	
    public double[] features(STFT stft, long startFrame, int length) 
    {
        double[] curFrame;
        double[] avgSpecCentroid = new double[1];
        double num = 0;
        double den = 0;

        for(int frame=0; frame<length; frame++) 
        {
            num = 0;  den = 0;
            curFrame = stft.getFrame(startFrame+frame);
            for(int band=0; band<stft.getRows(); band++) 
            {
                double freqCenter = band*(stft.samplingRate/2)/(stft.getRows()-1);
                // convert back to linear power
                double p = Math.pow(10,curFrame[band]/10);

                num += freqCenter*p;
                den += p;
            }
            avgSpecCentroid[0] += num/(length*den);
        }
        
        return avgSpecCentroid;
    }

	public String description()
	{
        return "Computes the average spectral center of mass of a chunk's frames.";
	}
}