---

SpectralStability.java

/*
 *  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;

public class SpectralStability extends FeatureExtractor 
{
        public double[] features(STFT stft, long startFrame, int length) 
        {
                int numBands = stft.getRows();
                double[] currFrame;
                double[] prevFrame = null;
                double lastEnergy = 0.0;
                double[] deltaSum = {0.0};

                //we'll sum the deltas in each bin from frame to frame
                //we'll return that total delta, maybe it'll act as an
                //indicator of the stability of the chunk...
                
                for (int frame = 0; frame < length; frame++)
                {               
                        currFrame = stft.getFrame(startFrame+frame);
                        
                        for (int bin = 0; bin < numBands; bin++)
                        {
                                double delta = 0.0;
                                //skip first frame!
                                if (prevFrame != null)
                                         delta = Math.abs(prevFrame[bin] - currFrame[bin]);
                                
                                //if (bin == 5 && prevFrame != null)
                                        //System.out.println("delta: " + delta);
                                
                                //this is a threshold of some sort...
                                if (delta < 5.0)
                                        delta = 0.0;
                                        
                                deltaSum[0] += delta;
                        }
                        
                        prevFrame = currFrame;
                }
                
                //normalize for frame length
                deltaSum[0] /= length;
                
                return deltaSum;
        }
  
        public String description()
        {
                return "Tracks the stability of the spectral energy within each chunk of sound. " 
            + "More spectrally stable chunks are more likely to be pitched material.";
        }
}

---