Fig. 1.

Block diagram of a linear system. When the input is an ideal impulse, δ(t), the response is the transport function, h(t). The ideal impulse, δ(t) or delta function, has area of one unit at time zero and the input is zero at all other times—that is, it is a tall, slim spike. This is illustrated in the left upper panel of Figure 3. When the input is any function which is not an impulse, f(t), the output, g(t), is formed by the convolution of f(t) and h(t). The asterisk denotes the process of convolution.