The human ear is the ultimate receiver of sound waves. When the alternating pressure of sound waves reaches the outer ear, the tympanic membrane can be adjusted to the frequency of the incident sound waves rate vibration. These vibrations are amplified by several ossicles, and transmitted to the nerve endings through the fluid in the inner ear, and finally to the cerebral cortex and produces the sensation of sound. Human recognition of voice is mainly based on the pitch, the size and tone of the voice. These three basic properties are called the three elements of sound. The pitch mainly depends on the frequency of the sound, the higher the frequency the higher the pitch, the higher the pitch.
At the same time, the tone is also related to the sound pressure level and composition. The size of the sound can be expressed by the loudness level. It is related to the frequency and sound pressure level. The timbre reflects a characteristic of the composite sound, which is mainly composed of the various frequency components and their intensities of the composite sound, which are determined by the frequency spectrum. The audible range of the human ear has a certain degree of frequency, loudness and the upper and lower limits,etc.