User`s guide

1 Data Processing
Use resample to decimate the signal before estimating the spectrum and plot
the frequency response, as follows:
g3 = spa(resample(y,1,4));
figure
ffplot(g1,g3)
The following figure shows that the estimated spectrum of the resampled
signal has the same amplitude as the original spectrum. Thus, there is no
indication of foldin g effects when you use
resample to eliminate aliasing.
No Folding Effec ts Wh en Using resample
See Also
For a detailed discussion about h andling disturbances, se e the chapter on
preprocessing data in System Identification: Theory for the User,Second
Edition, by Lennart Ljung, Prentice Hall PTR, 1999.
1-106