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Modifying Input Signals for Estimation

When the frequency response estimation produces unexpected results, you can try modifying the input signal properties in the ways described in Troubleshooting Frequency Response Estimation.

Modifying Sinestream Input Signal Using Linear Analysis Tool

Add Frequency Points to Sinestream Input Signal

This example shows how to add frequency points to an existing sinestream input signal using the Linear Analysis Tool.

  1. Create a sinestream input signal, in_sine1, as shown in Create Sinestream Signals Using Linear Analysis Tool.

  2. Double-click in_sine1 in the Linear Analysis Workspace area of the Linear Analysis Tool.

    The Edit sinestream dialog box opens.

  3. In the Frequency content viewer, click in the Frequency content toolbar.

    The Add frequencies dialog box opens.

  4. Enter the frequency range of the points to be added.

  5. Click OK to add the specified frequency points to in_sine1.

Delete Frequency Point from Sinestream Input Signal

This example shows how to delete frequency points from an existing sinestream input signal using the Linear Analysis Tool.

  1. Create a sinestream input signal, in_sine1, as shown in Create Sinestream Signals Using Linear Analysis Tool.

  2. Double-click in_sine1 in the Linear Analysis Workspace area of the Linear Analysis Tool.

    The Edit sinestream dialog box opens.

  3. In the Frequency content viewer, select the frequency point to delete.

    The selected point appears blue.

      Tip   To select multiple frequency points, click and drag across the frequency points of interest.

  4. Click in the Frequency content toolbar to delete the selected frequency point(s) from the Frequency content viewer.

  5. Click OK to save the modified input signal.

Modify Parameters for a Frequency Point in Sinestream Input Signal

This example shows how to modify signal parameters of an existing sinestream input signal using the Linear Analysis Tool.

  1. Create a sinestream input signal, in_sine1, as shown in Create Sinestream Signals Using Linear Analysis Tool.

  2. Double-click in_sine1 in the Linear Analysis Workspace area of the Linear Analysis Tool.

    The Edit sinestream dialog box opens.

  3. In the Frequency content viewer, select the frequency point(s) to delete.

    The selected point(s) appears blue.

  4. Enter the new values for the signal parameters.

    If the parameter value is <mixedvalue>, the parameter has different values for some of the frequency points selected.

  5. Click OK to save the modified input signal.

Modifying Sinestream Input Signal (MATLAB Code)

For example, suppose that you used a sinestream input signal, and the output at a specific frequency did not reach steady state. In this case, you can modify the characteristics of the sinestream input at the corresponding frequency.

input.NumPeriods(index)=NewNumPeriods;
input.SettlingPeriods(index)=NewSettlingPeriods;

where index is the frequency value index of the sine wave you want to modify. NewNumPeriods and NewSettlingPeriods are the new values of NumPeriods and SettlingPeriods, respectively.

To modify several signal properties at a time, you can use the set command. For example:

input = set(input,'NumPeriods',NewNumPeriods,...
                  'SettlingPeriods',NewSettlingPeriods)

After modifying the input signal, repeat the estimation.

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