Time Varying Filter (Thresholding) Express VI

LabVIEW 2014 Advanced Signal Processing Toolkit Help

Edition Date: June 2014

Part Number: 372656C-01

»View Product Info
Download Help (Windows Only)

Owning Palette: Time Frequency Transform VIs

Requires: Advanced Signal Processing Toolkit

Uses the thresholding method to perform time-varying filtering in the joint time-frequency domain.

Example

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
Data SourceSpecifies whether this Express VI reads data from a block diagram input terminal or from a file. From terminal specifies that this Express VI reads data from a block diagram input terminal. From file specifies that this Express VI reads data from a file. This Express VI can read data from waveform, WAV, or TXT files.
File Path ConfigurationContains the following options:
  • File path—Specifies and displays the path to the file from which this Express VI reads data. This option is available only when you select From file in the Data Source section.
  • Prompt to choose a file each time this VI runs—Specifies whether this Express VI displays a dialog box that prompts you to select a file each time this Express VI runs. This option is available only when you select the From file option in the Data Source section.
Gabor Transform SettingsContains the following options:
  • Analysis and synthesis window—Displays the analysis window and the synthesis window. This VI uses the analysis window and the synthesis window for the Gabor transform and the Gabor expansion, respectively. To accurately characterize the local properties of a signal in the joint time-frequency domain, the analysis window and the synthesis window must match as closely as possible.
  • N (frequency bins)—Specifies the number of carrier frequencies of the Gabor elementary functions. The frequency sampling interval of the signal in the time-frequency plane is fs/N (frequency bins), where fs is the sampling rate of the signal. This VI sets N (frequency bins) to a power of 2 and greater than or equal to dM (time steps). The ratio between N (frequency bins) and dM (time steps) is called the oversampling rate. For stable reconstruction, the oversampling rate must be greater than or equal to 1.
  • dM (time steps)—Specifies the time shift, in samples, between elementary functions. The time sampling interval of the signal in the time-frequency domain is dM (time steps)/fs, where fs is the sampling rate of the signal. This VI sets dM (time steps) to a power of 2.
  • Gaussian window length—Specifies the window length of the Gabor elementary functions. This VI sets Gaussian window length to a power of 2 automatically. Gaussian window length must be greater than or equal to N (frequency bins).
Filter SettingsContains the following options:
  • Threshold—Specifies the amplitude of the threshold for the Gabor coefficients. This VI sets all the coefficients whose amplitudes are less than the amplitude of the threshold, (Cmax – Cminthreshold, to 0, where Cmax is the maximum amplitude of the Gabor coefficients, and Cmin is the minimum amplitude of the Gabor coefficients.
    • Threshold value—Specifies the amplitude of the threshold for the Gabor coefficients.
  • NI Vision installed—Indicates if NI Vision is installed. The de-noise operation for the mask is available only when NI Vision is installed.
  • Noise level—Removes the small particles in the joint time-frequency representation plot. The functionality to remove small particles requires NI Vision. This VI removes from the joint time-frequency domain all the particles whose areas are smaller than row×column×noise level, where row and column are the row size and the column size of the Gabor coefficients. Refer to the TFA Discrete Gabor Transform VI for information about how the sizes of Gabor coefficients relate to dM (time steps) and N (frequency bins).
    • Noise level value—Removes the small particles in the joint time-frequency representation plot. The functionality to remove small particles requires NI Vision.
Data Type and Display ModeContains the following options:
  • Data type—Specifies the data type of the input signal. Data type is available only when you select From terminal in Data Source. When you select From file in Data Source, this Express VI determines the type of input signal based on the contents of the file.
  • Display mode—Specifies the display mode of complex signals. Display mode is available only when you select complex in Data type.
Gabor Coefficients and WaveformDisplays the magnitude of the Gabor coefficients in the upper graph and the time-domain signal in the lower graph. Contains the following options:
  • dB—Specifies whether this VI displays the magnitude of Gabor coefficients in decibels or in a linear scale.
  • Gabor Coefficients—Displays the magnitude of the Gabor coefficients on an intensity graph.
  • Signals—Displays the input signal and the filtered signal.

Block Diagram Inputs

ParameterDescription
error in (no error)Describes error conditions that occur before this node runs.
SignalSpecifies the block diagram terminal of the signal you want to load. This input is available only if you select the From terminal option in the Data Source section.
File pathSpecifies the file path of the data you want to load. This input is available only when you select the From file option in the Data Source section.

Block Diagram Outputs

ParameterDescription
error outContains error information. This output provides standard error out functionality.
Filtered SignalReturns the filtered signal.

This Express VI operates similarly to the following VIs and functions:

TFA Discrete Gabor Transform
TFA Dual Window
TFA Discrete Gabor Expansion

Example

Refer to the Offline Noise Reduction with Time Varying Filter VI in the labview\examples\Time Frequency Analysis\TFAApplications directory for an example of using the Time Varying Filter (Thresholding) Express VI.

WAS THIS ARTICLE HELPFUL?

Not Helpful