CrossSpectrum (FPScript)
Computes the windowed Fourier cross-spectrum between two data sets.
Syntax
CrossSpectrum(SignalA, SignalB, [ SpectrumType = SPECTRUM_DBNORM ], [ Window = WIN_HANNING+WIN_NORMALIZEAMPLITUDE ], [ Adjustment ], [ FFTLength = 0 ] [ , Peaks ])
The syntax of the CrossSpectrum 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, data matrix, 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, data matrix, 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 spectral 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 SPECTRUM_DBNORM. |
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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+WIN_NORMALIZEAMPLITUDE. |
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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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FFTLength |
The length of the Fourier transform. Zero padding applies if the FFT length is greater than the data length. The valid range is from the data length to the maximum limit of FFT. The default value is -1, which sets the FFT length equal to the next highest power of two. The default value is 0, which sets the FFT length equal to the data length. Permitted data structures are scalar value. All integral data types are permitted. The value must be greater or equal to -1 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
CrossSpectrum('Signal A', 'Signal B', SPECTRUM_AMPLITUDE, WIN_COS3MINSIDELOBE + WIN_NORMALIZEPOWER, 3, 0)
Calculates the cross spectrum from signal A and signal B. Amplitude is selected as the spectrum type. The window used is Cos 3 Minimum Sidelobe -71dB W=3, normalized to the power. The FFT length is set to the data length. This is an example from the Cross Spectral Analysis Tutorial.