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Causal signals and causal system

by reddvoid
Tags: causal, fourier, hilbert, laplace, signals
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Jan21-13, 07:49 AM
P: 99
Is there a difference between causal signal and causal system ?
I got this doubt because

consider a system h(t) whose out put depends on present and past inputs only for all t (- infinity to + infinity ) so this system is a causal system

now if we treat this as a signal and since it exists from -infinity to+ infinity so it will be a non-causal signal. . . .

which one is correct ?
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Jan21-13, 10:47 AM
P: 140
Causality in systems makes the most sense. Causality in signals doesn't make that much sense.

Causality in systems determines whether a system relies on future information of a signal x[n+1].

When talking about "causality" in signals, we mean whether they are zero to the left of t=0 or zero to the right of t=0.

A causal signal is zero for t<0
A non-causal zero has values present for t<0.
Anti-causal signals are zero for t>0.

However, the reason why this doesn't really make sense is that if you have a signal, the time t=0 can be chosen arbitrarily.
Jan21-13, 11:51 AM
P: 99
Got it :) thank you for clarifying :)

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