Computes the Choi-Williams Distribution (CWD) of signal. Wire data to the signal input to determine the polymorphic instance to use or manually select the instance.


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Inputs/Outputs

  • c1ddbl.png signal —

    signal specifies the input signal.

  • cnclst.png time-frequency sampling info —

    time-frequency sampling info specifies the density to use to sample the signal in the joint time-frequency domain and defines the size of the resulting 2D time-frequency array.

  • ci32.png time steps —

    time steps specifies the sampling period, in samples, along the time axis in the joint time-frequency domain. The default is -1, which specifies that this VI adjusts time steps automatically so that no more than 512 rows exist in spectrogram.

  • ci32.png frequency bins —

    frequency bins specifies the number of bins along the frequency axis to sample the signal in the joint time-frequency domain. frequency bins must be a power of 2 and greater than 0. The scale info output contains the actual sampling period in hertz along the frequency axis.

  • cdbl.png alpha —

    alpha specifies the relationship between resolution and cross-term interference. alpha must be greater than or equal to 0.

  • cerrcodeclst.png error in (no error) —

    error in describes error conditions that occur before this node runs. This input provides standard error in functionality.

  • cbool.png analytic signal? (T) —

    analytic signal? specifies whether to convert the real input signal to the corresponding analytic signal. The default is TRUE.

  • cdbl.png sampling rate —

    sampling rate specifies the sampling rate of signal in hertz. sampling rate must be greater than 0, or this VI sets sampling rate to 1 automatically. The default is 1.

  • i2ddbl.png spectrogram —

    spectrogram returns the quadratic time-frequency representation of the signal. Each row corresponds to the instantaneous power spectrum at a certain time.

  • ifxdt.png scale info —

    scale info returns the time scale and the frequency scale information of the time-frequency representation, including the time offset, the time interval between every two contiguous rows, the frequency offset, and the frequency interval between every two contiguous columns of spectrogram. Use the TFA Get Time and Freq Scale Info VI to return detailed information about the time scale and the frequency scale.

  • ierrcodeclst.png error out —

    error out contains error information. This output provides standard error out functionality.

    • TFA Choi-Williams Distribution Details

    CWD is a type of Cohen's class distribution and is the smooth version of the Wigner-Ville Distribution (WVD). CWD has better readability than WVD but worse time-frequency resolution, because CWD suppresses the cross-term interference between two signal components that have a large difference in central time or central frequency. However, CWD does not suppress the cross-term interference between two signal components that have the same central time or the same central frequency. Therefore, for large values of the signal length, this VI requires a long computation time and more memory. National instruments recommends that you limit signal to 15,000 samples.

    Examples

    Refer to the Marginal Condition VI in the labview\examples\Time Frequency Analysis\TFAFunctions directory for an example of using the TFA Choi-Williams Distribution VI.