ABSTRACT
Sound usually originates from the motion or vibration of an object. This motion is impressed upon the surrounding medium as a pattern of changes in pressure. The pressure changes are transmitted through the medium and may be heard as sound. The instruments used to measure the magnitudes of sounds, such as microphones, normally respond to changes in air pressure. However, the auditory system can deal with a huge range of sound pressures. This makes it inconvenient to deal with sound pressures directly. Instead a logarithmic measure expressing the ratio of two pressures is used - the decibel. The cochlea is divided along its length by the basilar membrane, which moves in response to sound. The response of the basilar membrane to sinusoidal stimulation takes the form of a travelling wave which moves along the membrane, with an amplitude that increases at first and then decreases rather abruptly.
