Computes the fast Fourier transform (FFT) of a sequence.
A Boolean that specifies whether to reset the internal state of the node.
True | Resets the internal state of the node. |
False | Does not reset the internal state of the node. |
This input is available only if you wire a double-precision, floating-point number or a complex double-precision, floating-point number to x.
Default: False
Input signal.
This input accepts the following data types:
Length of the FFT you want to perform.
This input changes to m if you wire a 2D array of double-precision, floating-point numbers or a 2D array of complex double-precision, floating-point numbers to x.
Node Behavior When x is a 1D Array of Numbers
When you wire a 1D array of double-precision, floating-point numbers or a 1D array of complex double-precision, floating-point numbers to x, if FFT size is greater than the number of elements in x, this node adds zeros to the end of x to match the size of FFT size. If FFT size is less than the number of elements in x, this node uses only the first n elements in x to perform the FFT, where n is FFT size. If FFT size is less than or equal to 0, this node uses the length of x as the FFT size.
Node Behavior When x is a Single Data Point
When you wire a double-precision, floating-point number or a complex double-precision, floating-point number to x, if FFT size is greater than sample length, this node collects data according to sample length but adds zeros to the end of the data set to match the size of FFT size. If FFT size is less than sample length, this node ignores sample length and uses only the first n elements in the data set to perform the FFT, where n is FFT size. If FFT size is less than or equal to 0, this node uses sample length as the FFT size.
Default: -1
Number of rows of the 2D FFT. This node truncates or zero-pads x to an m × n array before performing the FFT.
This input is available only if you wire a 2D array of double-precision, floating-point numbers or a 2D array of complex double-precision, floating-point numbers to x.
Default: -1
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 or a complex double-precision, floating-point number to x.
Default: 100
Number of columns of the 2D FFT. This node truncates or zero-pads x to an m × n array before performing the FFT.
This input is available only if you wire a 2D array of double-precision, floating-point numbers or a 2D array of complex double-precision, floating-point numbers to x.
Default: -1
A Boolean that determines whether the DC component is at the center of the FFT of the input sequence.
True | The DC component is at the center of the FFT{x}. |
False | The DC component is not at the center of the FFT{x}. |
This input is available only if you wire one of the following data types to x:
How This Input Affects 1D FFT
The following table illustrates the pattern of the elements of FFT{x} with various length of the FFT, when shift? is False. Y is FFT{x} and n is the length of the FFT:
n is even (k = n/2) | n is odd (k = (n-1)/2) | ||
---|---|---|---|
Array Element | Corresponding Frequency | Array Element | Corresponding Frequency |
Y _{0} | DC component | Y _{0} | DC component |
Y _{1} | Δf | Y _{1} | Δf |
Y _{2} | 2Δf | Y _{2} | 2Δf |
Y _{3} | 3Δf | Y _{3} | 3Δf |
$\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ |
Y _{ k-2} | (k - 2)Δf | Y _{ k-2} | (k - 2)Δf |
Y _{ k-1} | (k - 1)Δf | Y _{ k-1} | (k - 1)Δf |
Y _{ k } | Nyquist Frequency | Y _{ k } | kΔf |
Y _{ k+1} | -(k - 1)Δf | Y _{ k+1} | -kΔf |
Y _{ k+2} | -(k - 2)Δf | Y _{ k+2} | -(k - 1)Δf |
$\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ |
Y _{ n-3} | -3Δf | Y _{ n-3} | -3Δf |
Y _{ n-2} | -2Δf | Y _{ n-2} | -2Δf |
Y _{ n-1} | -Δf | Y _{ n-1} | -Δf |
The following table illustrates the pattern of the elements of FFT{x} with various length of the FFT, when shift? is True. Y is FFT{x} and n is the length of the FFT:
n is even (k = n/2) | n is odd (k = (n-1)/2) | ||
---|---|---|---|
Array Element | Corresponding Frequency | Array Element | Corresponding Frequency |
Y _{0} | -(Nyquist Frequency) | Y _{0} | -kΔf |
Y _{1} | -(k - 1)Δf | Y _{1} | -(k - 1)Δf |
Y _{2} | -(k - 2)Δf | Y _{2} | -(k - 2)Δf |
Y _{3} | -(k - 3)Δf | Y _{3} | -(k - 3)Δf |
$\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ |
Y _{ k-2} | -2Δf | Y _{ k-2} | -2Δf |
Y _{ k-1} | -Δf | Y _{ k-1} | -Δf |
Y _{ k } | DC component | Y _{ k } | DC component |
Y _{ k+1} | Δf | Y _{ k+1} | Δf |
Y _{ k+2} | 2Δf | Y _{ k+2} | 2Δf |
$\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ | $\begin{array}{c}\cdot \\ \cdot \\ \cdot \end{array}$ |
Y _{ n-3} | (k - 3)Δf | Y _{ n-3} | (k - 2)Δf |
Y _{ n-2} | (k - 2)Δf | Y _{ n-2} | (k - 1)Δf |
Y _{ n-1} | (k - 1)Δf | Y _{ n-1} | kΔf |
How This Input Affects 2D FFT
Default: False
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
FFT of the input signal.
This output can be a 1D or 2D array of complex double-precision, floating-point numbers.
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.
For 1D signals, this node computes the discrete Fourier transform (DFT) of the input sequence with a fast Fourier transform algorithm. The 1D DFT is defined as:
where x is the input sequence, N is the number of elements of x, and Y is the transform result.
The frequency resolution, or the frequency spacing between the components of Y, is:
where f _{ s } is the sampling frequency.
For 2D signals, this node computes the discrete Fourier transform (DFT) of the input matrix. This node performs a 1D FFT on the rows of the input matrix and then performs a 1D FFT on the columns of the output of the preceding step. The DFT of an M-by-N matrix is defined as:
where x is the input matrix and Y is the transform result.
Where This Node Can Run:
Desktop OS: Windows
FPGA: Not supported
Web Server: Not supported in VIs that run in a web application