Causal (Periodic) Signals
A signal
may be defined as causal when
for all ``negative-time'' samples (e.g., for
when
is even). Thus, the signal
is causal while
is not.
For causal signals, zero-padding is equivalent to simply
appending zeros to the original signal. For example,
![$\displaystyle \hbox{\sc ZeroPad}_{10}([1,2,3,0,0]) = [1,2,3,0,0,0,0,0,0,0].
$](http://www.dsprelated.com/josimages_new/mdft/img1241.png)
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