WindowFunction.java

/*
 * Copyright (C) 2011 Jacquet Wong
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.musicg.dsp;

/**
 * Window functions generator
 * 
 * @author Jacquet Wong
 *
 */
public class WindowFunction {

	public static final int RECTANGULAR = 0;
	public static final int BARTLETT = 1;
	public static final int HANNING = 2;
	public static final int HAMMING = 3;
	public static final int BLACKMAN = 4;

	int windowType = 0; // defaults to rectangular window

	public WindowFunction() {
	}

	public void setWindowType(int wt) {
		windowType = wt;
	}

	public void setWindowType(String w) {
		if (w.toUpperCase().equals("RECTANGULAR"))
			windowType = RECTANGULAR;
		if (w.toUpperCase().equals("BARTLETT"))
			windowType = BARTLETT;
		if (w.toUpperCase().equals("HANNING"))
			windowType = HANNING;
		if (w.toUpperCase().equals("HAMMING"))
			windowType = HAMMING;
		if (w.toUpperCase().equals("BLACKMAN"))
			windowType = BLACKMAN;
	}

	public int getWindowType() {
		return windowType;
	}

	/**
	 * Generate a window
	 * 
	 * @param nSamples	size of the window
	 * @return	window in array
	 */
	public double[] generate(int nSamples) {
		// generate nSamples window function values
		// for index values 0 .. nSamples - 1
		int m = nSamples / 2;
		double r;
		double pi = Math.PI;
		double[] w = new double[nSamples];
		switch (windowType) {
		case BARTLETT: // Bartlett (triangular) window
			for (int n = 0; n < nSamples; n++)
				w[n] = 1.0f - Math.abs(n - m) / m;
			break;
		case HANNING: // Hanning window
			r = pi / (m + 1);
			for (int n = -m; n < m; n++)
				w[m + n] = 0.5f + 0.5f * Math.cos(n * r);
			break;
		case HAMMING: // Hamming window
			r = pi / m;
			for (int n = -m; n < m; n++)
				w[m + n] = 0.54f + 0.46f * Math.cos(n * r);
			break;
		case BLACKMAN: // Blackman window
			r = pi / m;
			for (int n = -m; n < m; n++)
				w[m + n] = 0.42f + 0.5f * Math.cos(n * r) + 0.08f
						* Math.cos(2 * n * r);
			break;
		default: // Rectangular window function
			for (int n = 0; n < nSamples; n++)
				w[n] = 1.0f;
		}
		return w;
	}
}