Computes the fast Fourier transform (FFT) of the input sequence X. Wire data to the X input to determine the polymorphic instance to use or manually select the instance.


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Inputs/Outputs

  • c2dcdb.png X —

    X is the complex valued input sequence.

  • cbool.png shift? —

    shift? specifies whether the DC component is at the center of FFT {X}. The default is FALSE.

  • ci32.png m —

    m specifies the number of rows of the 2D FFT. This VI truncates or zero-pads X to an m-by-n array before performing the FFT.

  • ci32.png n —

    n specifies the number of columns of the 2D FFT. This VI truncates or zero-pads X to an m-by-n array before performing the FFT.

  • i2dcdb.png FFT {X} —

    FFT {X} is the 2D FFT of X.

    If the input signal is in volts (V), FFT {X} has units of volts. If the input signal is not in volts, FFT {X} has units of the input signal unit. This VI returns the phase in radians.

  • ii32.png error —

    error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

    • 2D FFT

    For 2D signals, the FFT VI computes the discrete Fourier transform (DFT) of the input matrix. This VI 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:

    for u = 0, 1, …, M–1, v=0, 1, …, N–1

    where x is the input matrix and Y is the transform result.

    The illustration below shows the effect of shift? on the 2D FFT result:

    2D input signals FFT without shift FFT with shift

    Related Information

    Output Units for FFT-Based Vis

    Examples

    Refer to the following example files included with LabVIEW.

    • labview\examples\Signal Processing\Transforms\FFT and Power Spectrum Units.vi