Wavelet Toolbox    

Continuous Analysis Using the Graphical Interface

We now use the Continuous Wavelet 1-D tool to analyze the same noisy sinusoidal signal we examined earlier using the command line interface in Continuous Analysis Using the Command Line.

Starting the Continuous Wavelet 1-D Tool.   

  1. From the MATLAB prompt, type:

    The Wavelet Toolbox Main Menu appears.

  1. Click the Continuous Wavelet 1-D menu item.

    The continuous wavelet analysis tool for one-dimensional signal data appears.

Loading a Signal.   

  1. Choose the FileLoad Signal menu option.
  2. When the Load Signal dialog box appears, select the demo MAT-file noissin.mat, which should reside in the MATLAB directory toolbox/wavelet/wavedemo. Click the OK button.

    The noisy sinusoidal signal is loaded into the Continuous Wavelet 1-D tool.

    The default value for the sampling period is equal to 1 (second).

Performing a Continuous Wavelet Transform.   

To start our analysis, let's perform an analysis using the db4 wavelet at scales 1 through 48, just as we did using command line functions in the previous section.

  1. In the upper right portion of the Continuous Wavelet 1-D tool, select the db4 wavelet and scales 1-48.

  2. Click the Analyze button.

    After a pause for computation, the tool displays the coefficients plot, the coefficients line plot corresponding to the scale a = 24, and the local maxima plot, which displays the chaining across scales (from a = 48 down to a = 1) of the coefficients local maxima.

Viewing Wavelet Coefficients Line.   

  1. Select another scale a = 40 by clicking in the coefficients plot with the right mouse button. See step 9 below to know, more precisely, how to select the desired scale.

    Click the New Coefficients Line button, the tool updates the plot.

Viewing Maxima Line.   

  1. Click the Refresh Maxima Line button, the local maxima plot displays the chaining across scales of the coefficients local maxima from a = 40 down to a = 1.
  2. Hold down the right mouse button over the coefficients plot, the position of the mouse is given by the Info frame (located at the bottom of the screen) in terms of location (X) and scale (Sca).

Switching from Scale to Pseudo-Frequency Information.   

  1. Using the radio button on the right part of the screen, select Frequencies instead of Scales. Again hold down the right mouse button over the coefficients plot, the position of the mouse is given in terms of location (X) and frequency (Frq) in Hertz.

    This facility allows you to interpret scale in terms of an associated pseudo-frequency, which depends on the wavelet and the sampling period.

  1. Deselect the last two plots using the check boxes in the Selected Axes frame.

Zooming in on Detail.   

  1. Drag a rubber band box (by holding down the left mouse button) over the portion of the signal you want to magnify.
  2. Click the X+ button (located at the bottom of the screen) to zoom horizontally only.
    The Continuous Wavelet 1-D tool enlarges the displayed signal and coefficients plot.

As with the command line analysis on the preceding pages, you can change the scales or the analyzing wavelet and repeat the analysis. To do this, just edit the necessary fields and press the Analyze button.

Viewing Normal or Absolute Coefficients.   

The Continuous Wavelet 1-D tool allows you to plot either the absolute values of the wavelet coefficients, or the coefficients themselves.

More generally, the coefficients coloration can be done in several different ways. For more details on the Coloration Mode, see Controlling the Coloration Mode.

  1. Choose either one of the absolute modes or normal modes from the Coloration Mode menu. In normal modes, the colors are scaled between the minimum and maximum of the coefficients. In absolute modes, the colors are scaled between zero and the maximum absolute value of the coefficients.

    The coefficients plot is redisplayed in the mode you select.


 Continuous Analysis Using the Command Line Importing and Exporting Information from the Graphical Interface