This chapter discusses the relationships between some of the engineering descriptions of sound and the psychological or subjective descriptions. The human ear is marvelous mechanism for detecting sound. Connected to the cochlea are the semicircular canals which are the balance mechanism and unrelated to hearing. The ear can be divided into three main parts: the outer, middle, and inner ear. The hair cells sense the shearing motion and if the stimulus is great enough the neuron to which each hair cell is attached sends an impulse along the nerve fiber to the brain cortex. A further experiment has been performed on the loudness of pure tones. The masking effect is different when the masking noise is a pure tone from when it is a band of noise. Central masking is masking which occurs in one ear when noise is presented to the other. Background noise usually causes people to speak louder and those with conduction deafness can then often hear.