Computes the cross power spectrum of two signals.
A value that affects the output coefficients when window type is Kaiser, Gaussian, or Dolph-Chebyshev.
If window type is any other type of window, this node ignores this input.
This input represents the following information for each type of window:
This input is available only if you wire one of the following data types to signal x or signal y.
Default: NaN—Causes this node to set beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 for a Dolph-Chebyshev window
Time-domain window to apply to the signal.
Name | Value | Description |
---|---|---|
Rectangle | 0 | Applies a rectangle window. |
Hanning | 1 | Applies a Hanning window. |
Hamming | 2 | Applies a Hamming window. |
Blackman-Harris | 3 | Applies a Blackman-Harris window. |
Exact Blackman | 4 | Applies an Exact Blackman window. |
Blackman | 5 | Applies a Blackman window. |
Flat Top | 6 | Applies a Flat Top window. |
4 Term B-Harris | 7 | Applies a 4 Term B-Harris window. |
7 Term B-Harris | 8 | Applies a 7 Term B-Harris window. |
Low Sidelobe | 9 | Applies a Low Sidelobe window. |
Blackman Nutall | 11 | Applies a Blackman Nutall window. |
Triangle | 30 | Applies a Triangle window. |
Bartlett-Hanning | 31 | Applies a Bartlett-Hanning window. |
Bohman | 32 | Applies a Bohman window. |
Parzen | 33 | Applies a Parzen window. |
Welch | 34 | Applies a Welch window. |
Kaiser | 60 | Applies a Kaiser window. |
Dolph-Chebyshev | 61 | Applies a Dolph-Chebyshev window. |
Gaussian | 62 | Applies a Gaussian window. |
Force | 64 | Applies a Force window. |
Exponential | 65 | Applies an Exponential window. |
Default: Rectangle
Length of each set of data. The node performs computation for each set of data.
sample length must be greater than zero.
This input is available only if you wire a double-precision, floating-point number to signal x or signal y.
Default: 100
Error conditions that occur before this node runs.
The node responds to this input according to standard error behavior.
Standard Error Behavior
Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.
Default: No error
Sample period of the time-domain signal in seconds.
Set this input to 1/fs, where fs is the sampling frequency of the time-domain signal.
This input is available only if you wire one of the following data types to signal x or signal y.
Default: 1
Cross power spectrum of the input signals.
Start frequency, in Hz, of the spectrum.
Frequency resolution, in Hz, of the spectrum.
Cross power spectrum of the signals.
Error information.
The node produces this output according to standard error behavior.
Standard Error Behavior
Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.
The cross power, ${S}_{xy}\left(f\right)$, of the signals x(t) and y(t) is defined as
where
This node uses the FFT or DFT routine to compute the cross power spectrum, which is given by
where S _{ x y } represents the complex sequence cross spectrum and n is the number of samples that can accommodate input sequences signal x and signal y.
The largest cross power that this node can compute by the FFT is 2^{23} (8,388,608 or 8M).
Some textbooks define the cross power spectrum as ${S\prime}_{xy}\left(f\right)=X\left(f\right)Y*\left(f\right)$. If you prefer this definition of cross power to the one specified in this node, take the complex conjugate of the output sequence cross spectrum, because this node operates on the real and imaginary portions separately.
When the number of samples in the inputs signal x and signal y are equal and are a valid power of 2, such that $n=m={2}^{k}$ for k = 1, 2, 3,..., 23, this node makes direct calls to the FFT routine to compute the complex cross power sequence. This technique is efficient in both execution time and memory management because this node performs the operations in place.
When the number of samples in the inputs signal x and signal y are not equal, this node first resizes the smaller sequence by padding it with zeros to match the size of the larger sequence. If this size is a valid power of 2, such that $\mathrm{max}(n,m)={2}^{k}$ for k = 1, 2, 3,..., 23, this node computes the cross power spectrum using the FFT. Otherwise, this node uses the slower DFT to compute the cross power spectrum. Thus, the size of the complex output sequence is defined by $\text{size}=\mathrm{max}(n,m)$.
Where This Node Can Run:
Desktop OS: Windows
FPGA: Not supported
Web Server: Not supported in VIs that run in a web application