When listening to speech or music we are aware that the sound is composed of many different frequencies which are constantly changing and also varying in intensity. This constantly modulating sound is encoded into electrical discharges by the cochlea. The coded information then passes as a series of electrical discharges along the auditory pathways and is processed and refined in the auditory centres. Finally all the data decoded, possibly in the auditory cortex to produce the sensation we perceive as musical notes or someone speaking.