Editing Weighting filter (section)

=== Loudness measurements ===
In the measurement of loudness, for example, an [[A-weighting]] filter is commonly used to emphasize frequencies around 3–6&nbsp;kHz where the human ear is most sensitive, while [[Attenuation|attenuating]] very high and very low frequencies to which the ear is insensitive. The aim is to ensure that measured loudness corresponds well with subjectively perceived loudness.
A-weighting is only really valid for relatively quiet sounds and for pure tones as it is based on the 40-phon [[Fletcher–Munson curves|Fletcher–Munson]] [[equal-loudness contour]].<ref name=":3"/> The [[B-weighting curve|B]] and [[C-weighting curve|C curve]]s were intended for louder sounds (though they are less used) while the [[D-weighting curve|D curve]] is used in assessing loud aircraft noise ([[IEC 537]]).  B curves filter out more medium loudness levels when compared to an A curves.<ref name=":3"/> This curve is rarely ever used in the assessment or monitoring of noise levels anymore.<ref name=":0"/> C curves differ from both A and B in the fact that they filter less of the lower and higher frequencies.<ref name=":3" /> The filter is a much flatter shape and is used in sound measurement in especially loud and noisy environments.<ref name=":3"/> A weighted curves follow a 40 phon curve while C weighted follows a 100 phon curve.<ref name=":0"/> The three curves differ not in their measurement of exposure levels, but in the frequencies measured. A weighted curves allow more frequencies equal to or less than 500&nbsp;Hz through, which is most representative of the human ear.<ref name=":0"/>