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TarsosDSP library
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/*
*      _______                       _____   _____ _____  
*     |__   __|                     |  __ \ / ____|  __ \ 
*        | | __ _ _ __ ___  ___  ___| |  | | (___ | |__) |
*        | |/ _` | '__/ __|/ _ \/ __| |  | |\___ \|  ___/ 
*        | | (_| | |  \__ \ (_) \__ \ |__| |____) | |     
*        |_|\__,_|_|  |___/\___/|___/_____/|_____/|_|     
*                                                         
* -------------------------------------------------------------
*
* TarsosDSP is developed by Joren Six at IPEM, University Ghent
*  
* -------------------------------------------------------------
*
*  Info: http://0110.be/tag/TarsosDSP
*  Github: https://github.com/JorenSix/TarsosDSP
*  Releases: http://0110.be/releases/TarsosDSP/
*  
*  TarsosDSP includes modified source code by various authors,
*  for credits and info, see README.
* 
*/

/*
*  Copyright (c) 2007 - 2008 by Damien Di Fede 
*
*   This program is free software; you can redistribute it and/or modify
*   it under the terms of the GNU Library General Public License as published
*   by the Free Software Foundation; either version 2 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 Library General Public License for more details.
*
*   You should have received a copy of the GNU Library General Public
*   License along with this program; if not, write to the Free Software
*   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

package be.tarsos.dsp.util.fft;

/**
 * A Blackman window function.
 *
 * @author Damien Di Fede
 * @author Corban Brook
 * @see   The Blackman Window
 */
public class BlackmanWindow extends WindowFunction {
	protected float alpha;

	/**
	 * Constructs a Blackman window.
	 * 
	 * @param alpha
	 */
	public BlackmanWindow(float alpha) {
		this.alpha = alpha;
	}

	/** Constructs a Blackman window with a default alpha value of 0.16 */
	public BlackmanWindow() {
		this(0.16f);
	}

  protected float value(int length, int index){
      float a0 = (1 - this.alpha) / 2f;
      float a1 = 0.5f;
      float a2 = this.alpha / 2f;

      return a0 - a1 * (float) Math.cos(TWO_PI * index / (length - 1)) + a2 * (float) Math.cos(4 * Math.PI * index / (length - 1));
  }
}