There are three factors that affect people's experience and perception of sound:
Sound levels are expressed in decibels (dB). A 10 dB increase corresponds to a perceived doubling of the noise level. A 1 dB increase is the smallest audible change that can be detected. The table indicates typical sound levels.
The hearing damage potential of a noise is also dependent on the duration of exposure to it. Damage risk is usually assessed on the basis of an eight-hour daily exposure cycle.
Frequency is expressed in Hertz (Hz). Many noise sources contain a wide range of frequencies. However, the human ear does not respond equally to sound pressure levels over different frequencies. To compensate for the ear's varying sensitivity sound is measured using dB(A), an internationally agreed weighting which mimics the responsiveness of the human ear. Sound level meters incorporate a filter for measuring in dB(A).