/*
*
      
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*
     
|__
   
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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 <ddf@compartmental.net>
 
*
 
*
   
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 Window function represents a curve which is applied to a sample buffer to
 
* reduce the introduction of spectral leakage in the Fourier transform.
 
*
 
* <p>
 
* <b>Windowing</b>
 
* <p>
 
* Windowing is the process of shaping the audio samples before transforming
 
* them to the frequency domain. The Fourier Transform assumes the sample buffer
 
* is is a repetitive signal, if a sample buffer is not truly periodic within
 
* the measured interval sharp discontinuities may arise that can introduce
 
* spectral leakage. Spectral leakage is the speading of signal energy across
 
* multiple FFT bins. This "spreading" can drown out narrow band signals and
 
* hinder detection.
 
* <p>
 
* A <a href=" http://en.wikipedia.org/wiki/Window_function">windowing
 
* function</a> attempts to reduce spectral leakage by attenuating the measured
 
* sample buffer at its end points to eliminate discontinuities. If you call the
 
* <code>window()</code> function with an appropriate WindowFunction, such as
 
* <code>HammingWindow()</code>, the sample buffers passed to the object for
 
* analysis will be shaped by the current window before being transformed. The
 
* result of using a window is to reduce the leakage in the spectrum somewhat.
 
* <p>
 
* <code>WindowFunction</code> handles work associated with various window
 
* functions such as the Hamming window. To create your own window function you
 
* must extend <code>WindowFunction</code> and implement the
 
* {@link #value(int, int) value} method which defines the shape of the window
 
* at a given offset. <code>WindowFunction</code> will call this method to apply
 
* the window to a sample buffer. The number passed to the method is an offset
 
* within the length of the window curve.
 
*
 
* @author Damien Di Fede
 
* @author Corban Brook
 
*
 
*/

public abstract class WindowFunction {

	
/** The float value of 2*PI. Provided as a convenience for subclasses. */
	
protected static final float TWO_PI = (float) (2 * Math.PI);
	
protected int length;

	
public WindowFunction() {
	
}

	
/**
	 
* Apply the window function to a sample buffer.
	 
*
 

	 
* @param samples
	 
*
            
a sample buffer
	 
*/

	
public void apply(float[] samples) {
		
this.length = samples.length;

		
for (int n = 0; n < samples.length; n++) {
			
samples[n] *= value(samples.length, n);
		
}
	
}

	
/**
	 
* Generates the curve of the window function.
	 
*
 

	 
* @param length
	 
*
            
the length of the window
	 
* @return the shape of the window function
	 
*/

	
public float[] generateCurve(int length) {
		
float[] samples = new float[length];
		
for (int n = 0; n < length; n++) {
			
samples[n] = 1f * value(length, n);
		
}
		
return samples;
	
}

	
protected abstract float value(int length, int index);
}