Editing Loudness (section)

== Explanation ==
The perception of loudness is related to [[sound pressure level]] (SPL), frequency content and duration of a sound.<ref>{{cite journal |author-last=Poulsen |author-first=Torben |title=Loudness of tone pulses in a free field |journal=The Journal of the Acoustical Society of America |date=1981 |volume=69 |issue=6 |pages=1786–1790 |bibcode=1981ASAJ...69.1786P |doi=10.1121/1.385915 |pmid=7240592 |s2cid=7190836 |url=http://orbit.dtu.dk/ws/files/3586037/Torben.pdf}}</ref> The relationship between SPL and loudness of a single tone can be approximated by [[Stevens's power law]] in which SPL has an exponent of 0.67.{{efn|The relationship between loudness and energy ''intensity'' of sound can therefore be approximated by a power function with an exponent of 0.3.}} A more precise model known as the ''Inflected [[Exponential function]]'',<ref>{{cite book |author-last=Goldstein |author-first=E. Bruce |title=Encyclopedia of Perception Vol. 1 |date=2009 |publisher=Sage |isbn=9781412940818 |page=147 |url=https://books.google.com/books?id=6M3NSNm6MlkC&q=inflected+exponential+loudness&pg=PA147}}</ref> indicates that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels.<ref>{{cite journal |author-last1=Florentine |author-first1=Mary |author-link1=Mary Florentine |author-last2=Epstein |author-first2=Michael |author-link2=Michael J. Epstein |title=To honor Stevens and repeal his law |journal=Proceedings of the International Society for Psychophysics |date=2006 |volume=22 |url=https://scholar.google.com/citations?user=DYB56FMAAAAJ&hl=en&oi=ao#d=gs_md_cita-d&p=&u=%2Fcitations%3Fview_op%3Dview_citation%26hl%3Den%26user%3DDYB56FMAAAAJ%26citation_for_view%3DDYB56FMAAAAJ%3Ad1gkVwhDpl0C%26tzom%3D420}}</ref>

The sensitivity of the human ear changes as a function of frequency, as shown in the [[Equal-loudness contour|equal-loudness graph]]. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud, and different curves pertain to different sound pressure levels. It also shows that humans with normal hearing are most sensitive to sounds around 2–4&nbsp;kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency.<ref>{{cite journal |author-last=Olson |author-first=Harry |title=The Measurement of Loudness |journal=Audio Magazine |date=1972 |url=https://scholar.google.com/scholar?cluster=8587541427905974401&hl=en&as_sdt=0,5&sciodt=0,5#d=gs_qabs&p=&u=%23p%3DgVBJEG4TLXcJ}}</ref>

Historically, loudness was measured using an ear-balancing method with an [[audiometer]] in which the [[amplitude]] of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated.<ref>{{citation |doi=10.1093/oso/9780198887768.003.0004 |title=Measuring Noise: From Ear-Balance to Self-Registration}}</ref> Contemporary standards for measurement of loudness are based on the summation of energy in [[critical band]]s.<ref>As described in [[IEC]] 532, [[DIN]] 45631 and ASA/[[ANSI]] S3.4</ref>