Wavelet Denoise Express VI

LabVIEW 2014 Advanced Signal Processing Toolkit Help

Edition Date: June 2014

Part Number: 372656C-01

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Owning Palette: Feature Extraction VIs

Requires: Advanced Signal Processing Toolkit

Performs noise reduction for 1D signals by using the discrete wavelet transform (DWT) or undecimated wavelet transform (UWT).

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.
Original and Denoised SignalDisplays the original signal and the signal after denoising.
Transform SettingsContains the following options:
  • Transform type—Specifies to use the discrete wavelet transform (DWT) or undecimated wavelet transform (UWT) to denoise the signal.
  • Wavelet—Specifies the wavelet type to use for the discrete wavelet analysis. The default is db02. The options include two types: orthogonal (Haar, Daubechies (dbxx), Coiflets (coifx), Symmlets (symx)) and biorthogonal (Biorthogonal (biorx_x), including FBI (bior4_4 (FBI))), where x indicates the order of the wavelet. The higher the order, the smoother the wavelet. The orthogonal wavelets are not redundant and are suitable for signal or image denoising and compression. The biorthogonal wavelets usually have the linear phase property and are suitable for signal or image feature extraction.
  • Levels—Specifies the number of levels in the discrete wavelet analysis. Levels must be a positive integer no greater than log2(Ls), where Ls is the length of the signal.
  • Analysis wavelet—Displays the analysis wavelet function.
Threshold SettingsContains the following options:
  • Soft threshold—Specifies to use the soft thresholding method. The default is to use the soft thresholding method. If you remove the checkmark from the Soft threshold checkbox, this VI uses the hard thresholding method.
  • Thresholding rule—Specifies the threshold selection rules. The default is Universal, which indicates that this VI sets the threshold to sqrt(2×log(Ls)), where Ls is the signal length. If you select SURE, this VI uses the principle of Stein's Unbiased Risk Estimate (SURE) to estimate the threshold. If you select Hybrid, this VI finds a compromise between the SURE method and the Universal method. When the signal-to-noise ratio of the noisy signal is very low, this VI uses the Universal method to estimate the threshold. If you select Minimax, this VI uses the minimax principle to estimate the threshold.
  • Rescaling method—Specifies the method to use to estimate the noise variance at each level. The default is single level, which indicates that the noise is white and that this VI estimates the noise standard deviation from the wavelet coefficients at the first level. This VI uses the noise variance to rescale the threshold. Therefore, you can update the thresholds with the noise variance. Selecting one indicates that the noise is white with unit variance. Selecting multiple levels indicates that the noise does not have to be white and that this VI estimates the noise standard deviation at each level independently.
  • Option for approx.—Specifies the operation for the approximation coefficients from the wavelet decomposition. The default is None, which indicates that this VI keeps the approximation coefficients unchanged. If you select threshold, this VI applies the same thresholding operation to the approximation coefficients. If you select detrend, this VI sets the approximation coefficients to 0.
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.

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
Denoised SignalReturns the estimated signal after denoising.
error outContains error information. This output provides standard error out functionality.

Example

Refer to the Noise Reduction VI in the labview\examples\Wavelet Analysis\WAApplications directory for an example of using the Wavelet Denoise Express VI.

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