The purpose of weighting here is to emphasise the parts of the audible spectrum that our ears perceive most readily, and attenuate the parts that contribute less to our perception of loudness, in order to get a measured figure that correlates well with subjective effect.
The ITU-R 468 noise weighting was devised specifically for this purpose, and is widely used in broadcasting, especially in the UK and Europe.
A-weighting is also used, especially in the United States,[1][dubious – discuss] though this is only really valid for the measurement of tones, not noise, and is widely incorporated into sound level meters.
In telecommunications, noise weightings are used by agencies concerned with public telephone service, and various standard curves are based on the characteristics of specific commercial telephone instruments, representing successive stages of technological development.
The same weighting nomenclature and units are used in military versions of commercial noise measuring sets.