/*
* @(#)SpectralFlux.java 1.0 April 5, 2005.
*
* McGill Univarsity
*/
package org.vocvark.AudioFeatures;
import org.vocvark.DataTypes.FeatureDefinition;
/**
* A feature extractor that extracts the Spectral Flux from a window of samples and
* the preceeding window. This is a good measure of the amount of spectral chagne
* of a signal.
* <p/>
* <p>Spectral flux is calculated by first calculating the difference between
* the current value of each magnitude spectrum bin in the current window from
* the corresponding value of the magnitude spectrum of the previous window.
* Each of these differences is then squared, and the result is the sum of the
* squares.
* <p/>
* <p>No extracted feature values are stored in objects of this class.
*
* @author Cory McKay
*/
public class SpectralFlux
extends FeatureExtractorBaseImpl {
/* CONSTRUCTOR **************************************************************/
/**
* Basic constructor that sets the definition and dependencies (and their
* offsets) of this feature.
*/
public SpectralFlux() {
String name = "Spectral Flux";
String description = "A measure of the amount of spectral change in a signal. " +//\n" +
"Found by calculating the change in the magnitude spectrum " +//\n" +
"from frame to frame.";
boolean is_sequential = true;
int dimensions = 1;
definition = new FeatureDefinition(name,
description,
is_sequential,
dimensions);
dependencies = new String[2];
dependencies[0] = "Magnitude Spectrum";
dependencies[1] = "Magnitude Spectrum";
offsets = new int[2];
offsets[0] = 0;
offsets[1] = -1;
}
/* PUBLIC METHODS **********************************************************/
/**
* Extracts this feature from the given samples at the given sampling
* rate and given the other feature values.
* <p/>
* <p>In the case of this feature, the sampling_rate parameter is ignored.
*
* @param samples The samples to extract the feature from.
* @param sampling_rate The sampling rate that the samples are
* encoded with.
* @param other_feature_values The values of other features that are
* needed to calculate this value. The
* order and offsets of these features
* must be the same as those returned by
* this class's getDependencies and
* getDependencyOffsets methods respectively.
* The first indice indicates the feature/window
* and the second indicates the value.
* @throws Exception Throws an informative exception if
* the feature cannot be calculated.
* @return The extracted feature value(s).
*/
public double[] extractFeature(double[] samples,
double sampling_rate,
double[][] other_feature_values)
throws Exception {
double[] this_magnitude_spectrum = other_feature_values[0];
double[] previous_magnitude_spectrum = other_feature_values[1];
double sum = 0.0;
for (int bin = 0; bin < this_magnitude_spectrum.length; bin++) {
double difference = this_magnitude_spectrum[bin]
- previous_magnitude_spectrum[bin];
double differences_squared = difference * difference;
sum += differences_squared;
}
double[] result = new double[1];
result[0] = sum;
return result;
}
/**
* Create an identical copy of this feature. This permits FeatureExtractor
* to use the prototype pattern to create new composite features using
* metafeatures.
*/
public Object clone() {
return new SpectralFlux();
}
}