ddf.minim.analysis
Class WindowFunction

java.lang.Object
  ddf.minim.analysis.WindowFunction

Direct Known Subclasses:

BartlettHannWindow, BartlettWindow, BlackmanWindow, CosineWindow, GaussWindow, HammingWindow, HannWindow, LanczosWindow, RectangularWindow, TriangularWindow

public abstract class WindowFunction
extends java.lang.Object

A Window function represents a curve which is applied to a sample buffer to reduce the introduction of spectral leakage in the Fourier transform.

Windowing

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.

A windowing function attempts to reduce spectral leakage by attenuating the measured sample buffer at its end points to eliminate discontinuities. If you call the window() function with an appropriate WindowFunction, such as HammingWindow(), 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.

WindowFunction handles work associated with various window functions such as the Hamming window. To create your own window function you must extend WindowFunction and implement the value method which defines the shape of the window at a given offset. WindowFunction 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, Corban Brook

Field Summary

protected int	length
protected static float	TWO_PI The float value of 2*PI.

Constructor Summary

WindowFunction()

Method Summary

void	apply(float[] samples) Apply the window function to a sample buffer.
float[]	generateCurve(int length) Generates the curve of the window function.
protected abstract float	value(int length, int index)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TWO_PI

protected static final float TWO_PI

The float value of 2*PI. Provided as a convenience for subclasses.

See Also:

Constant Field Values

length

protected int length

Constructor Detail

WindowFunction

public WindowFunction()

Method Detail

apply

public void apply(float[] samples)

Apply the window function to a sample buffer.

Parameters:

samples - a sample buffer

generateCurve

public float[] generateCurve(int length)

Generates the curve of the window function.

Parameters:

length - the length of the window

Returns:

the shape of the window function

value

protected abstract float value(int length,
                               int index)