What is noise and how is it considered?

Noise is sound that is unwanted and, when measured for its effect on people, considers the response of the human ear. The human ear hears sound pressures over a wide range but also perceives how loud a sound is differently depending on the pitch or frequency of the sound.

The loudness of a noise is most often described in decibels, which are measured on a logarithmic scale, corresponding to the way our ears interpret sound pressures. When considering the noise exposure levels for people, the A-weighted frequency scale is most often used, which most closely approximates how the human ear responds to different sound frequencies. Different noise metrics such as the Day-Night Level (DNL) or Sound Exposure Level (SEL) can then be created to take into account different ways of looking at noise.