User`s guide

Resampling Data
The data. Int erSample property of the iddata object is taken into account
during resampling (for example, first-order hold or zero-o rde r hold). For more
information, see “iddata Properties” on p age 1-50.
Resampling Data Without Aliasing Effects
Typically, yo u d ecimate a signal to remove the high-freque ncy c o n tributions
that result from noise from the total energy . Ideally, you want to remove the
energy contribution due to noise and preserve the energy density of the signal.
The command
resample performs the decimation w ith out aliasi n g effects.
This command includes a factor of T to normalize the spectrum and preserve
the energy d ensity after decimation. For more information about spectrum
normalization, see “Understanding Spectrum Norm alization” on page 3-11.
If you use manual decimation instead of
resample—by picking every fourth
sample from the signal, for example— the energy contributions from higher
frequencies are folded back into the lower frequencies. Because the total
signal energy is preserve d by this operation and this energy must now be
squeezed into a smaller frequency range, the amplitude of the spectrum at
each frequency increases. Thus, the energy density of the decimated signal
is not constant.
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