For an input x(t), the output of an linear system is given by the superposition integral y(t) = Z 1 x( )h (t) d. 1. If the system is also time invariant, the result is a convolution integral. Z 1. y(t) = x( )h(t ) d. 1. For a sinusoidal input at frequency f ,the output is. a sinusoid at the same frequency, scaled in amplitude, and.