To create a noise spectrum plot for parametric linear models
in the app, 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 app. 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**

Action | Command | |
---|---|---|

Display the confidence interval. | To display the dashed lines on either side of the nominal model curve, select **Options**>**Show confidence intervals**. Select this option again to hide the confidence intervals.To change the confidence value, select **Options**>**Set % confidence level**, and choose a value from the list.To enter your own confidence level, select **Options**>**Set confidence level**>**Other**. Enter the value as a probability (between 0 and 1) or as the number of standard deviations of a Gaussian distribution.
| |

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 Enter the frequency vector using any one of following methods: MATLAB ^{®}expression, such as`[1:100]*pi/100` or`logspace(-3,-1,200)` . Cannot contain variables in the MATLAB workspace.Row vector of values, such as `[1:.1:100]`
| |

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. |

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