Signal representation and system response

Abstract

Perhaps the most familiar example of a signal is a musical sound. Plucking a string on a guitar causes that string to vibrate up and down as illustrated in Figure 1.1(a). Plotting the vertical position of one point on the string as a function, x(), of time, t, reveals the periodic motion of the string (Figure 1.1(b)). The motion of the string alters the pressure in the air around the string and the pressure of the air will oscillate in sympathy with the movement of the string. The pressure wave radiates from the guitar towards the microphone which converts the fluctuations in pressure to an electrical voltage oscillation (Figure 1.2(a)). All of these oscillations are examples of signals. All of them carry information. Listening to a recording of the electrical signal, most people would be able to identify the instrument being played, i.e. would be able to distinguish between a guitar and a piano. Some people might be able to identify the pitch and hence the note being played.