The Motion Picture Experts Group has developed standards for representing combined audio-visual communication. For audio, MPEG uses psychacoustic principles, that is, it takes into account how the brain perceives sound quality, and what frequency ranges ears are most sensitive to.

Humans can hear sound in the range of 20 Hz to 20 KHz, but are most sensitive to sounds from 2 KHz to 4 KHz, not coincidentally, the same range as the human voice. Because softer sounds in close frequency to louder sounds are not really heard, these softer sounds can also be eliminated.

The human eardrum "hears" as a result of a disturbance in air pressure.

It is important to distinguish between frequency, a physical measure, and its perception by the ear, pitch.

Similarly, we distinguish between amplitude, a physical measure, and its perception by the ear, loudness or volume.

For multimedia, there is no need to understand audio aspects that humans cannot perceive. Digital audio saves space by not storing what cannot be perceived or perceived well.

Scientists have discovered, however, that:

The perceived pitch of a tone can be changed by changing its amplitude.

The perceived volume of a tone can be changed by changing frequency.

Sounds can mask other sounds in the same way that bright headlights mask our vision. The effect depends on the differences in frequency of the two sounds.