Coherence (FPScript)
Computes the coherence spectrum between two data sets.
Syntax
Coherence(SignalA, SignalB, [ SpectrumType = COHERENCE_MAGNITUDE2 ], [ Window = WIN_HANNING ], [ Adjustment ], [ SegmentLength = 0 ], [ OverlapOrGap = 50 ], [ FFTLength = 0 ] [ , Peaks ])
The syntax of the Coherence function consists of the following parts:
Part |
Description |
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SignalA |
The first data set to be analyzed. Permitted data structures are data series, signal und signal series. All real data types are permitted, except calendar time und time span. Void values are not permitted in this argument. For the X component additional restrictions do apply.The values must have a constant positive spacing. Void values are not permitted in this argument. If the argument is a list, then the function is executed for each element of the list and the result is also a list. |
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SignalB |
The second data set to be analyzed. Permitted data structures are data series, signal und signal series. All real data types are permitted, except calendar time und time span. Void values are not permitted in this argument. For the X component additional restrictions do apply.The values must have a constant positive spacing. Void values are not permitted in this argument. If the argument is a list, then the function is executed for each element of the list and the result is also a list. |
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SpectrumType |
The coherence or Signal to Noise Ratio format to be computed. The argument SpectrumType can have the following values:
Permitted data structures are scalar value. All integral data types are permitted. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. If this argument is omitted, it will be set to the default value COHERENCE_MAGNITUDE2. |
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Window |
The fixed or adjustable data window to be applied to the data. The argument Window can have the following values:
Permitted data structures are scalar value. All integral data types are permitted. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. If this argument is omitted, it will be set to the default value WIN_HANNING. |
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Adjustment |
The one-sided Fourier width as a multiple of the frequency interval. The valid range is window specific within 1.0 to 6.0. The default is 1.5 for a tapered cosine window and 3.0 for all other adjustable data windows. Permitted data structures are scalar value. All real data types are permitted. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. |
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SegmentLength |
The length of individual data segments. The valid range is between 2 and the data length / 2. The default value of 0 sets the segment length to the data length / 4. Permitted data structures are scalar value. All integral data types are permitted. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. If this argument is omitted, it will be set to the default value 0. |
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OverlapOrGap |
If this argument is specified as a positive number, then it specifies the percentage overlap of the individual data segments. If it is specified as a negative number, then its amount specifies the gap between the individual data segments in samples. Permitted data structures are scalar value. All real data types are permitted. The value must be less or equal to 95. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. If this argument is omitted, it will be set to the default value 50. |
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FFTLength |
The length of the Fourier transform. Zero padding applies if the FFT length is greater than the segment length. The valid range is from the segment length to the maximum limit of FFT. The default value is 0, which sets the FFT length equal to the segment length. Permitted data structures are scalar value. All integral data types are permitted. The value must be greater or equal to 0 and less or equal to 2147483648. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. If this argument is omitted, it will be set to the default value 0. |
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Peaks |
If specified, then only band-interpolated peaks of the spectrum are output. The peaks can be specified as a number or determined using a dB threshold. Specify a number as a positive number from 1 to 100 without a unit. You can specify a dB threshold as a quantity with the unit dB between 0.01 dB and 300 dB, or as a negative number between -0.01 and -300 without a unit. Permitted data structures are scalar value. All real data types are permitted. If the argument is a list, then the first element in the list is taken. If this is also a list, then the process is repeated. |
Remarks
The data structure of the result is a signal or signal series. If the argument SignalA is a data series or data matrix, then the X component of the result contains Nyquist-normalized frequencies. If both data sets have an X component, then these must be identical. The number of values in each data set and, in case of data matrices or signal series, also the number of columns must match. For example, you can combine a signal series with a signal. In this case the spectrum of the signal is combined with the spectra of each column in the signal series.
Available in
Option Spectral Analysis
Examples
Coherence('Signal A', 'Signal B', COHERENCE_MAGNITUDE2, WIN_COS3MINSIDELOBE + WIN_NORMALIZEPOWER, 3, 0, 50, 0)
Calculates the coherence spectrum of 'signal A' and 'signal B'. The window used is Cos 3 Minimum Sidelobe -71dB W=3, normalized to the power. The segment length amounts to data length/4, and the FFT length is set to the segment length. This is an example from the Cross Spectral Analysis Tutorial.