Systems that operate under real time conditions need to be causal - that is, they can only process present and past inputs. When no real time processing is needed the system can be non-causal.
a. Consider the case of averaging an input signal x[n] under real time conditions. Suppose you are given two different filters,
y[n] = 1/N S( x[n-k]; N-1:k=0 and y[n] = 1/N S(x[n-k]) ;N -1:k = N+1 Which one of these would you use and why?
b. If you are given a tape with the data, which of these two filters would you use? Why? Would you use either? Explain