marf.Preprocessing.FFTFilter
Class FFTFilter

java.lang.Object
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  +--marf.Preprocessing.Preprocessing
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        +--marf.Preprocessing.FFTFilter.FFTFilter

All Implemented Interfaces:

StorageManager

Direct Known Subclasses:

BandpassFilter, HighFrequencyBoost, HighPassFilter, LowPassFilter

public abstract class FFTFilter

extends Preprocessing

FFTFilter class

Implements filtering using FFT algorithm

Derivatives must set frequency response based on the type of filter they are.

Author:

Stephen Sinclair

Field Summary

protected double[]

freqResponse Frequency repsonse to be multiplied by the incoming value

Fields inherited from class marf.Preprocessing.Preprocessing

oSample

Constructor Summary

FFTFilter(Sample poSample)
FFTFilter Constructor

Method Summary

boolean	filter(double[] sample, double[] filtered) Perform a filter by the following algorithm: sample -> window -> FFT -> buffer buffer * frequency response buffer -> IFFT -> window -> sample Window used is square root of Hamming window, because the sum at half-window overlap is a constant, which avoids amplitude distortion from noise.
boolean	preprocess() FFTFilter implementation of preprocess()
void	setFrequencyResponse(double[] response) Sets frequency response.

Methods inherited from class marf.Preprocessing.Preprocessing

cropAudio, dump, getSample, normalize, removeNoise, removeSilence, restore

Methods inherited from class java.lang.Object

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

Field Detail

freqResponse

protected double[] freqResponse

Frequency repsonse to be multiplied by the incoming value

Constructor Detail

FFTFilter

public FFTFilter(Sample poSample)

FFTFilter Constructor

Parameters:

poSample - incoming sample

Method Detail

preprocess

public boolean preprocess()
                   throws PreprocessingException

FFTFilter implementation of preprocess()

It does call removeNoise() and removeSilence() if they were explicitly requested by an app before applying filtering.

Overrides:

preprocess in class Preprocessing

Returns:

true if there was something filtered out

Throws:

PreprocessingException -

setFrequencyResponse

public final void setFrequencyResponse(double[] response)

Sets frequency response. Derivatives must call this method in their constructors.

Parameters:

response - desired frequency response

Throws:

PreprocessingException -

filter

public final boolean filter(double[] sample,
                            double[] filtered)
                     throws PreprocessingException

Perform a filter by the following algorithm: sample -> window -> FFT -> buffer buffer * frequency response buffer -> IFFT -> window -> sample Window used is square root of Hamming window, because the sum at half-window overlap is a constant, which avoids amplitude distortion from noise. Also, start sampling at -responseSize/2, in order to avoid amplitude distortion of the first half of the first window. "filtered" must be at least as long as "sample"

Parameters:

sample - incoming sample analog data

filtered - will contain data after the filter was applied

Returns:

true if some filtering actually happened

Throws:

PreprocessingException -