Editing Weighting filter (section)

=== Environmental noise measurement ===
A-weighted [[decibel]]s are abbreviated '''dB(A)''' or '''dBA.''' When acoustic ([[calibrated]] microphone) measurements are being referred to, then the units used will be dB [[Sound pressure|SPL]] ([[sound pressure level]]) referenced to 20 micropascals = 0&nbsp;dB SPL.<ref name="FS1037"/><ref group="nb" name="NB_dBa"/>

The A-weighting curve has been widely adopted for environmental noise measurement, and is standard in many sound level meters (see [[ITU-R 468 noise weighting|ITU-R 468]] weighting for a further explanation).

A-weighting is also in common use for assessing potential [[Hearing impairment|hearing damage]] caused by loud noise, though this seems to be based on the widespread availability of sound level meters incorporating A-Weighting rather than on any good experimental evidence to suggest that such use is valid. The distance of the measuring microphone from a sound source is often "forgotten", when SPL measurements are quoted, making the data useless. In the case of environmental or [[aircraft noise]], distance need not be quoted as it is the level at the point of measurement that is needed, but when measuring [[refrigerator]]s and similar appliances the distance should be stated; where not stated it is usually one metre (1 m).  An extra complication here is the effect of a reverberant room, and so noise measurement on appliances should state "at 1 m in an open field" or "at 1 m in [[anechoic chamber]]". Measurements made outdoors will approximate well to anechoic conditions.{{Citation needed|date=June 2015}}

A-weighted SPL measurements of noise level are increasingly to be found on sales literature for domestic appliances such as refrigerators and freezers, and computer fans. Although the threshold of hearing is typically around 0&nbsp;dB SPL, this is in fact very quiet indeed, and appliances are more likely to have noise levels of 30 to 40&nbsp;dB SPL.