frequencywarper.java

来自「It is the Speech recognition software. 」· Java 代码 · 共 67 行

/*
 * Copyright 1999-2002 Carnegie Mellon University.  
 * Portions Copyright 2002 Sun Microsystems, Inc.  
 * Portions Copyright 2002 Mitsubishi Electric Research Laboratories.
 * All Rights Reserved.  Use is subject to license terms.
 * 
 * See the file "license.terms" for information on usage and
 * redistribution of this file, and for a DISCLAIMER OF ALL 
 * WARRANTIES.
 *
 */

package edu.cmu.sphinx.frontend.frequencywarp;

/**
 * Defines the Bark frequency warping function. This class provides
 * methods to convert frequencies from a linear scale to the bark
 * scale. The bark scale is originated from measurements of the
 * critical bandwidth. Please find more details in books about
 * psychoacoustics or speech analysis/recognition.
 *
 * @author <a href="mailto:[e-mail]">rsingh</a>
 * @version 1.0
 */
public class FrequencyWarper {
    

    /**
     * Default null constructor. No fields to be initialized.
     */
    /*
    public FrequencyWarper (){}
    */

   /**
     * Compute Bark frequency from linear frequency in Hertz.
     * The function is:
     * bark = 6.0*log(hertz/600 + sqrt((hertz/600)^2 + 1))
     *
     * @param hertz the input frequency in Hertz
     *
     * @return the frequency in a Bark scale
     *
     */
    public double hertzToBark(double hertz) {
	double x = hertz/600;
	return (6.0*Math.log(x + Math.sqrt(x*x + 1)));
    }


    /**
     * Compute linear frequency in Hertz from Bark frequency.
     * The function is:
     * hertz = 300*(exp(bark/6.0) - exp(-bark/6.0))
     *
     * @param bark the input frequency in Barks
     *
     * @return the frequency in Hertz
     *
     */
    public double barkToHertz(double bark) {
	double x = bark/6.0;
	return (300.0*(Math.exp(x)-Math.exp(-x)));
    }
    
}// FrequencyWarper