BlackmanWindow.java (2514B)
1 /* 2 * _______ _____ _____ _____ 3 * |__ __| | __ \ / ____| __ \ 4 * | | __ _ _ __ ___ ___ ___| | | | (___ | |__) | 5 * | |/ _` | '__/ __|/ _ \/ __| | | |\___ \| ___/ 6 * | | (_| | | \__ \ (_) \__ \ |__| |____) | | 7 * |_|\__,_|_| |___/\___/|___/_____/|_____/|_| 8 * 9 * ------------------------------------------------------------- 10 * 11 * TarsosDSP is developed by Joren Six at IPEM, University Ghent 12 * 13 * ------------------------------------------------------------- 14 * 15 * Info: http://0110.be/tag/TarsosDSP 16 * Github: https://github.com/JorenSix/TarsosDSP 17 * Releases: http://0110.be/releases/TarsosDSP/ 18 * 19 * TarsosDSP includes modified source code by various authors, 20 * for credits and info, see README. 21 * 22 */ 23 24 /* 25 * Copyright (c) 2007 - 2008 by Damien Di Fede <ddf@compartmental.net> 26 * 27 * This program is free software; you can redistribute it and/or modify 28 * it under the terms of the GNU Library General Public License as published 29 * by the Free Software Foundation; either version 2 of the License, or 30 * (at your option) any later version. 31 * 32 * This program is distributed in the hope that it will be useful, 33 * but WITHOUT ANY WARRANTY; without even the implied warranty of 34 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 35 * GNU Library General Public License for more details. 36 * 37 * You should have received a copy of the GNU Library General Public 38 * License along with this program; if not, write to the Free Software 39 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 40 */ 41 42 package be.tarsos.dsp.util.fft; 43 44 /** 45 * A Blackman window function. 46 * 47 * @author Damien Di Fede 48 * @author Corban Brook 49 * @see <a href="http://en.wikipedia.org/wiki/Window_function#Blackman_windows">The Blackman Window</a> 50 */ 51 public class BlackmanWindow extends WindowFunction { 52 protected float alpha; 53 54 /** 55 * Constructs a Blackman window. 56 * 57 * @param alpha 58 */ 59 public BlackmanWindow(float alpha) { 60 this.alpha = alpha; 61 } 62 63 /** Constructs a Blackman window with a default alpha value of 0.16 */ 64 public BlackmanWindow() { 65 this(0.16f); 66 } 67 68 protected float value(int length, int index){ 69 float a0 = (1 - this.alpha) / 2f; 70 float a1 = 0.5f; 71 float a2 = this.alpha / 2f; 72 73 return a0 - a1 * (float) Math.cos(TWO_PI * index / (length - 1)) + a2 * (float) Math.cos(4 * Math.PI * index / (length - 1)); 74 } 75 } 76