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Causal signals and causal system

  1. Jan 21, 2013 #1
    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 ?
  2. jcsd
  3. Jan 21, 2013 #2
    Re: causal signal sand causal system

    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.
  4. Jan 21, 2013 #3
    Re: causal signal sand causal system

    Got it :) thank you for clarifying :)
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