In signal processing, a shift invariant system is the discrete equivalent of a time-invariant system, defined such that if y ( n ) {\displaystyle y(n)} is the response of the system to x ( n ) {\displaystyle x(n)} , then y ( n − k ) {\displaystyle y(n-k)} is the response of the system to x ( n − k ) {\displaystyle x(n-k)} . That is, in a shift-invariant system, the contemporaneous response of the output variable to a given value of the input variable does not depend on when the input occurs; time shifts are irrelevant in this regard.