ddf.minim.analysis
Class FFT

java.lang.Object
  ddf.minim.analysis.FourierTransform
      ddf.minim.analysis.FFT

public class FFT
extends FourierTransform

FFT stands for Fast Fourier Transform. It is an efficient way to calculate the Complex Discrete Fourier Transform. There is not much to say about this class other than the fact that when you want to analyze the spectrum of an audio buffer you will almost always use this class. One restriction of this class is that the audio buffers you want to analyze must have a length that is a power of two. If you try to construct an FFT with a timeSize that is not a power of two, an IllegalArgumentException will be thrown.

Author:

Damien Di Fede

See Also:

FourierTransform, The Fast Fourier Transform

Field Summary

Fields inherited from class ddf.minim.analysis.FourierTransform

averages, avgPerOctave, bandWidth, BARTLETT, BARTLETTHANN, COSINE, HAMMING, HANN, imag, LANCZOS, LINAVG, LOGAVG, NOAVG, NONE, octaves, real, sampleRate, spectrum, timeSize, TRIANGULAR, TWO_PI, whichAverage, windowFunction

Constructor Summary

FFT(int timeSize, float sampleRate)
Constructs an FFT that will accept sample buffers that are timeSize long and have been recorded with a sample rate of sampleRate.

Method Summary

protected void	allocateArrays()
void	forward(float[] buffer) Performs a forward transform on buffer.
void	forward(float[] buffReal, float[] buffImag) Performs a forward transform on the passed buffers.
void	inverse(float[] buffer) Performs an inverse transform of the frequency spectrum and places the result in buffer.
void	scaleBand(int i, float s) Scales the amplitude of the ith frequency band by s.
void	setBand(int i, float a) Sets the amplitude of the ith frequency band to a.

Methods inherited from class ddf.minim.analysis.FourierTransform

avgSize, calcAvg, doWindow, fillSpectrum, forward, forward, forward, freqToIndex, getAverageCenterFrequency, getAvg, getBand, getBandWidth, getFreq, indexToFreq, inverse, inverse, linAverages, logAverages, noAverages, scaleFreq, setComplex, setFreq, specSize, timeSize, window

Methods inherited from class java.lang.Object

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

Constructor Detail

FFT

public FFT(int timeSize,
           float sampleRate)

Constructs an FFT that will accept sample buffers that are timeSize long and have been recorded with a sample rate of sampleRate. timeSize must be a power of two. This will throw an exception if it is not.

Parameters:

timeSize - the length of the sample buffers you will be analyzing

sampleRate - the sample rate of the audio you will be analyzing

Method Detail

allocateArrays

protected void allocateArrays()

Specified by:

allocateArrays in class FourierTransform

scaleBand

public void scaleBand(int i,
                      float s)

Description copied from class: FourierTransform

Scales the amplitude of the ith frequency band by s. You can use this to shape the spectrum before using inverse().

Specified by:

scaleBand in class FourierTransform

Parameters:

i - the frequency band to modify

s - the scaling factor

setBand

public void setBand(int i,
                    float a)

Description copied from class: FourierTransform

Sets the amplitude of the ith frequency band to a. You can use this to shape the spectrum before using inverse().

Specified by:

setBand in class FourierTransform

Parameters:

i - the frequency band to modify

a - the new amplitude

forward

public void forward(float[] buffer)

Description copied from class: FourierTransform

Performs a forward transform on buffer.

Specified by:

forward in class FourierTransform

Parameters:

buffer - the buffer to analyze

forward

public void forward(float[] buffReal,
                    float[] buffImag)

Performs a forward transform on the passed buffers.

Parameters:

buffReal - the real part of the time domain signal to transform

buffImag - the imaginary part of the time domain signal to transform

inverse

public void inverse(float[] buffer)

Description copied from class: FourierTransform

Performs an inverse transform of the frequency spectrum and places the result in buffer.

Specified by:

inverse in class FourierTransform

Parameters:

buffer - the buffer to place the result of the inverse transform in