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AvgMFCC.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 java.util.Arrays;

import com.meapsoft.STFT;

public class AvgMFCC extends AvgMelSpec 
{
    private int nceps = 13;

    // Default constructor - Use AvgMelSpec defaults
    public AvgMFCC() 
    {
        super();
    }


    public double[] features(STFT stft, long startFrame, int length) 
    {
        double[] mfccs = new double[nceps];
        Arrays.fill(mfccs, 0);

        // precompute DCT matrix
        int nmel = outDim;  
        double m = Math.sqrt(2.0/nmel);
        double[][] DCTcoeffs = new double[nmel][nceps];
        for(int i = 0; i < nmel; i++)
            for(int j = 0; j < nceps; j++)
                DCTcoeffs[i][j] = m*Math.cos(Math.PI*(j+1)*(i+.5)/(double)nmel);

        for(int frm = 0; frm < length; frm++)
        {
            double[] melSpec = super.features(stft, startFrame+frm, 1);
            
            // convert to cepstrum:
            for(int x = 0; x < melSpec.length; x++)
            {
                // convert from dB to plain old log magnitude
                melSpec[x] = melSpec[x]/10;  

                // take DCT
                for(int y = 0; y < mfccs.length; y++)
                    mfccs[y] = mfccs[y] + DCTcoeffs[x][y]*melSpec[x]/length;
            }
        }

        return mfccs;
    }

    public String description()
    {
        return "Computes the mean MFCCs of a chunk, a commonly used feature in speech recognition.";
    }
}

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