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FFT Power Spectrum and PSD (Power Spectral Density) (G Dataflow)

    Last Modified: January 9, 2017

    Computes the power spectral density of a time-domain signal.


    window parameter

    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:

    • Kaiser—Beta parameter
    • Gaussian—Standard deviation
    • Dolph-Chebyshev—The ratio, s, of the main lobe to the side lobe

    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


    window type

    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: Hanning


    restart averaging

    A Boolean specifying whether the node restarts the selected averaging process.

    True Restarts the averaging process.
    False Does not restart the averaging process.

    When you call this node for the first time, the averaging process restarts automatically. A typical case when you restart averaging is when a major input change occurs in the middle of the averaging process.

    Default: False



    The input signal.

    This input supports the following data types:

    • Waveform
    • Complex double-precision, floating-point waveform
    • 1D array of waveforms
    • 1D array of complex double-precision, floating-point waveforms

    dB on

    A Boolean specifying whether this node returns the results in decibels.

    True Returns the results in decibels.
    False Returns the results in the original units.

    Default: False


    averaging parameters

    Settings that define how this node computes the averaging.


    averaging mode

    The mode this node uses to compute the averaging.

    Name Description
    No averaging Does not use averaging.
    Vector averaging Uses vector averaging.
    RMS averaging Uses RMS averaging.
    Peak hold Uses peak hold averaging.

    Default: No averaging


    weighting mode

    Weighting mode for RMS and vector averaging.

    Name Description
    Linear Uses linear weighting.
    Exponential Uses exponential weighting.

    Default: Exponential


    number of averages

    Number of averages to use for RMS and vector averaging.

    If weighting mode is Exponential, the averaging process is continuous. If weighting mode is Linear, the averaging process stops after this node computes the specified number of averages.

    Default: 10


    error in

    Error conditions that occur before this node runs. The node responds to this input according to standard error behavior.

    Default: No error


    power spectral density

    Averaged power spectral density and the frequency scale.



    Start frequency, in Hz, of the spectrum.



    Frequency resolution, in Hz, of the spectrum.



    Magnitude of the averaged power spectral density.


    averaging done

    A Boolean that indicates whether the number of averages this node completed is greater than or equal to the specified number of averages.

    True The number of averages this node completed is greater than or equal to the specified number of averages.
    False The number of averages this node completed is less than the specified number of averages.

    averaging done is always True if averaging mode is No averaging.


    averages completed

    Number of averages this node completed.


    error out

    Error information. The node produces this output according to standard error behavior.

    Algorithm for Computing the Power Spectral Density

    This node completes the following steps to compute the power spectral density:

    1. Computes the FFT of the input signal.
    2. Forms the power spectral density of the input signal.
    3. Averages the current power spectral density with the power spectral densities computed in previous calls to the node since the last time the averaging process was restarted.
    4. Returns the averaged power spectral densities.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported

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