Class FFT

Inheritance
Object
FFT
Inherited Members
Namespace: TowseyLibrary
Assembly: TowseyLibrary.dll
Syntax
public sealed class FFT

Constructors

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FFT(Int32)

Declaration
public FFT(int windowSize)
Parameters
Type Name Description
Int32 windowSize
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FFT(Int32, FFT.WindowFunc)

Initializes a new instance of the FFT class. It is a wrapper for calling method that does the FFT. Window Power equals sum of squared window values.

Declaration
public FFT(int windowSize, FFT.WindowFunc w)
Parameters
Type Name Description
Int32 windowSize
FFT.WindowFunc w

Fields

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BlackmanHarris

Declaration
public static readonly FFT.WindowFunc BlackmanHarris
Field Value
Type Description
FFT.WindowFunc
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BlackmanNuttall

Declaration
public static readonly FFT.WindowFunc BlackmanNuttall
Field Value
Type Description
FFT.WindowFunc
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DefaultFftWindow

Declaration
public const string DefaultFftWindow = "HANNING"
Field Value
Type Description
String
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FlatTop

Declaration
public static readonly FFT.WindowFunc FlatTop
Field Value
Type Description
FFT.WindowFunc
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Hamming

The Hamming window reduces the immediate adjacent sidelobes (compared to the Hanning) but at the expense of increased distal side-lobes. https://en.wikipedia.org/wiki/Window_function.

Declaration
public static readonly FFT.WindowFunc Hamming
Field Value
Type Description
FFT.WindowFunc
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Hanning

See comment for Hanning that compares Hamming with Hanning. Our experience with analysis of environmental recordings, where we often up or down sample in order to calculate indices, is that the HANNING window is to be preferred and it was made the default in July 2020.

Declaration
public static readonly FFT.WindowFunc Hanning
Field Value
Type Description
FFT.WindowFunc
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KeyHammingWindow

Declaration
public const string KeyHammingWindow = "HAMMING"
Field Value
Type Description
String
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KeyHanningWindow

Declaration
public const string KeyHanningWindow = "HANNING"
Field Value
Type Description
String
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KeyNoWindow

Declaration
public const string KeyNoWindow = "NONE"
Field Value
Type Description
String
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Lanczos

Declaration
public static readonly FFT.WindowFunc Lanczos
Field Value
Type Description
FFT.WindowFunc
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Nuttall

Declaration
public static readonly FFT.WindowFunc Nuttall
Field Value
Type Description
FFT.WindowFunc

Properties

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CoeffCount

Declaration
public int CoeffCount { get; }
Property Value
Type Description
Int32
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WindowPower

Declaration
public double WindowPower { get; }
Property Value
Type Description
Double
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WindowSize

Declaration
public int WindowSize { get; }
Property Value
Type Description
Int32
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WindowWeights

Declaration
public double[] WindowWeights { get; }
Property Value
Type Description
Double[]

Methods

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Gauss(Double)

Declaration
public static FFT.WindowFunc Gauss(double sigma)
Parameters
Type Name Description
Double sigma
Returns
Type Description
FFT.WindowFunc
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GetWindowFunction(String)

Returns an FFT window function given the name of the window type.

Declaration
public static FFT.WindowFunc GetWindowFunction(string name)
Parameters
Type Name Description
String name

FFT window name.
Returns
Type Description
FFT.WindowFunc

FFT.WindowFunc.
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Invoke(Double[])

Invokes an FFT on the given data array. cdata contains the real and imaginary terms of the coefficients representing cos and sin components respectively. cdata is symmetrical about terms 512 & 513. Can ignore all coefficients 512 and above.

Declaration
public double[] Invoke(double[] data)
Parameters
Type Name Description
Double[] data

a single frame of signal values.
Returns
Type Description
Double[]
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Invoke(Double[], Int32)

Declaration
public double[] Invoke(double[] data, int offset)
Parameters
Type Name Description
Double[] data
Int32 offset
Returns
Type Description
Double[]
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InvokeDotNetFFT(Double[])

This .NET FFT library was downloaded from http://www.mathdotnet.com/Iridium.aspx The documentation and various examples of code are available at http://www.mathdotnet.com/doc/IridiumFFT.ashx WARNING: THIS METHOD HAS NOT BEEN RECENTLY TESTED.

Declaration
public double[] InvokeDotNetFFT(double[] data)
Parameters
Type Name Description
Double[] data
Returns
Type Description
Double[]

Extension Methods