This figure consists of two graphs.

Graph (a) shows x (as a function of t) against t. The graph line fluctuates randomly up and down, above and below the horizontal axis.

Graph (b) shows x[n] against n. It consists of a series of vertical lines along the horizontal axis at integer values of n – some extending above the axis and some below. Each line has a small filled circle at the end furthest from the axis. The distance between two vertical lines is labelled T.

◄ 3.2 Characteristics of discrete-time and continuous-time signals