Android Open Source - CopresenceDataCollector Cross Correlation

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Back to project page CopresenceDataCollector.

License

The source code is released under:

Copyright (c) 2014, Xiang Gao All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Re...

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Java Source Code

package org.sesy.coco.datacollector.audio;
/**//ww  w .  j a v  a 2 s. c  o  m
 *      This class serves for computing the cross correlation function (CCF).
 *      The computing is done using the FFT.
 *
 *      @author siniwitt 
 */
public class CrossCorrelation {

        /** Convolution object*/
        private Convolution conv;
        
        /** array containing the lags (x-axis of the CCF)*/
        private int[] lags;
        
        /** signal 2 in reverse order*/
        private double[] sig2Reverse;
        
        /** length of the correlation*/
        private int corrLength;
        
        /** length of the signal, if the signals are of equal lengths*/
        private int sigLength = 0;
        
        /** are the signals of equal lengths*/
        private boolean isEqualLength;
        
        /**
         * Construct a CrossCorrelation object, which
         * does the cross-correlation between two input signals
         * 
         * @param sig1 first signal
         * @param sig2 second signal
         */
        public CrossCorrelation(double[] sig1, double[] sig2) {
                sig2Reverse = new double[sig2.length];
                for(int i = 0; i < sig2.length; i++){
                        sig2Reverse[i] = sig2[sig2.length - 1 - i];
                }
                
                // the computing is done using fast convolution
                conv = new Convolution(sig1, sig2Reverse);
                lags = new int[conv.getFrameSize()];
                int sig1Length = sig1.length;
                int sig2Length = sig2.length;
                corrLength = sig1Length+sig2Length-1;
                
                if(sig1Length == sig2Length){
                        isEqualLength = true;
                        sigLength = sig1Length;
                }else{
                        isEqualLength = false;
                }
                
                if(!isEqualLength){
                        int diffLength = sig1Length - sig2Length;
                        for(int i = 0; i < (sig1Length+sig2Length-1); i++)
                                lags[i] = i - sig1Length + 2 + diffLength;
                }else{
                        for(int i = 0; i < corrLength; i++)
                                lags[i] = i - sig1Length + 1;
                }
        }
        
        /**
         * @return returns the framesize of the resulting cross-correlation
         */
        public int getFrameSize() {
                return conv.getFrameSize();
        }
        
        /**
         * @return returns the lags corresponding to the resulting
         * cross-correlation 
         */
        public int[] getLags(){
                return lags;
        }

        /**
         * Computes the Crosscorrelation using the FFT
         */
        public void getCCF(double[] ccf) {
                conv.computeResult(ccf);
                
                /*if(isEqualLength){
                        //normalizing like MATLABs xcorr 'unbiased' option
                        for(int i = 0; i < ccf.length; i++)
                                ccf[i] /= (double)(sigLength - Math.abs(lags[i]));
                } */
        }
        
}

Java Source Code List