The Noise spectrum plot is opened by checking the corresponding check box in the ident window.
The plots show the disturbance spectra of the selected models.
For input-output models the disturbance spectrum is defined as the spectrum of w in the description
y(t) = G(q) u(t) + w(t)
For time series models
y(t) = H(q) e(t)
the shown spectrum is that of y itself.
The output number (channel) selector (y1, etc.) refers to the chosen output component of the spectrum. Cross spectra between different outputs are not accessible.
(file idspect.hlp)