/**
* Copyright (C) 2001-2017 by RapidMiner and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapidminer.com
*
* This program is free software: you can redistribute it and/or modify it under the terms of the
* GNU Affero General Public License as published by the Free Software Foundation, either version 3
* of the License, or (at your option) any later version.
*
* This program 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
* Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License along with this program.
* If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.tools.math;
/**
* Creates a series of peaks (a spectrum) from the series of complex values calculated for example
* by a fourier transform. Since the FT input values must not be equivalent the magnitudes of the
* spectrum do not correspond to the real amplitudes. Like the human ear this filter tries to
* calculate more accurate values (see ERB or Bark filters).
*
* @author Ingo Mierswa
*/
public class SpectrumFilter {
public static final int NONE = 0;
public static final int ERB = 1;
public static final int LOG = 2;
public static final int LOG2 = 3;
private int weightType;
public SpectrumFilter(int weightType) {
this.weightType = weightType;
}
public Peak[] filter(Complex[] spectrum, int totalSize) {
Peak[] result = new Peak[spectrum.length];
for (int i = 0; i < result.length; i++) {
result[i] = new Peak(FastFourierTransform.convertFrequency(i, spectrum.length, totalSize), filterValue(
spectrum[i].getMagnitude(spectrum.length * 2), i));
}
return result;
}
private double filterValue(double value, int index) {
switch (weightType) {
case ERB:
return value * (21.4d * Math.log(0.00437d * index + 1.0d) / Math.log(10.0d));
case LOG:
return value * (10.0d * Math.log(index + 1) / Math.log(20.0d));
case LOG2:
return value * (0.7d * Math.log(5 * index + 1));
default:
return value;
}
}
}