WindowFunction.java

package com.codefixia.audio;

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

  public  final int RECTANGULAR = 0;
  public  final int BARTLETT = 1;
  public  final int HANNING = 2;
  public  final int HAMMING = 3;
  public  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;
  }
}