ABSTRACT
Strictly speaking, not all vibrations of this kind are sound; to be audible, the frequency must lie somewhere between about 20 and 20 000 Hz. The simplest of all vibrations are those in which the variations of pressure along the wave are sinusoidal as a function of time, in other words proportional to sin(2pft), where t is the lapsed time. In such a case we may describe the wave completely by means of its frequency and its amplitude, A, the value of the additional pressure at the peak of compression. We can also talk about the period of the wave, the time taken for one whole cycle (= 1/f).
