To create a noise spectrum plot for parametric linear models in the GUI, select the Noise spectrum check box in the Model Views area. For general information about creating and working with plots, see Working with Plots.
To include or exclude a model on the plot, click the corresponding model icon in the System Identification Tool GUI. Active models display a thick line inside the Model Board icon.
The following figure shows a sample Noise Spectrum plot.
The following table summarizes the Noise Spectrum plot settings.
Noise Spectrum Plot Settings
Display the confidence interval.
Change the frequency values for computing the noise spectrum.
The default frequency vector is 128 linearly distributed values, greater than zero and less than or equal to the Nyquist frequency.
Select Options > Frequency range and specify a new frequency vector in units of radians per second.
Enter the frequency vector using any one of following methods:
|Change frequency units between hertz and radians per second.||Select Style > Frequency (Hz) or Style > Frequency (rad/s).|
|Change frequency scale between linear and logarithmic.||Select Style > Linear frequency scale or Style > Log frequency scale.|
|Change amplitude scale between linear and logarithmic.||Select Style > Linear amplitude scale or Style > Log amplitude scale.|
(Multiple-output system only)
|Select the output by name in the Channel menu.|