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I know like this might seem like a trivial question but I am a bit confused with it. Take for example the the system y=x(n-10). Initially I thought this system was noncausal because n-10 means that the graph of the signal would be shifting 10 units to the right, meaning that the signal would be delayed by 10 seconds and so the output of the system would rely on a future value. However, apparently this system IS causal because if you take your time n and subtract 10 you arrive at 10 seconds in the past and thus the signal only relies on past values. Obviously, these two conclusions contradict each other. How can I reconcile them and make sense of this?

Andrew Schroeder
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  • y(n)=x(n-10) is just a system with memory... (think of a delay). Instead, y(n) = x(n+10) would be non causal, because the output depends on the inputs in the future. – next-hack Sep 10 '17 at 20:23
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    Here is the problem: "the signal would be delayed by 10 seconds and so the output of the system would rely on a future value". A delay does NOT rely on the future but on the past. – Curd Sep 10 '17 at 20:39

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