Editing Absolute threshold of hearing (section)

{{Short description|Minimum sound level that an average human can hear}}

The '''absolute threshold of hearing''' ('''ATH'''), also known as the '''absolute hearing threshold''' or '''auditory threshold''', is the minimum [[Sound intensity level|sound level]] of a [[pure tone]] that an average human ear with normal [[hearing]] can hear with no other sound present. The absolute threshold relates to the [[sound]] that can just be heard by the organism.<ref name="Durrant & Lovrinic 1984">Durrant J D., Lovrinic J H. 1984. ''Bases of Hearing Sciences''. Second Edition. United States of America: Williams & Wilkins</ref><ref name="Gelfand 2004">Gelfand S A., 2004. ''Hearing an Introduction to Psychological and Physiological Acoustics''. Fourth edition. United States of America: Marcel Dekker</ref> The absolute threshold is not a discrete point and is therefore classed as the point at which a sound elicits a response a specified percentage of the time.<ref name="Durrant & Lovrinic 1984"/>

The threshold of hearing is generally reported in reference to the [[Root mean square|RMS]] [[sound pressure]] of 20 [[micropascal]]s, i.e. 0&nbsp;dB SPL, corresponding to a [[sound intensity]] of 0.98&nbsp;pW/m<sup>2</sup> at 1 atmosphere and 25&nbsp;°C.<ref>RMS sound pressure <math>p</math> can be converted to plane wave sound intensity using <math>I=\frac{p^2}{\rho v}</math>, where ''ρ'' is the density of air and <math>v</math> is the [[speed of sound]]</ref> It is approximately the quietest sound a young human with undamaged hearing can detect at 1&nbsp;[[kHz]].<ref name="Gelfand, 1990">Gelfand, S A., 1990. ''Hearing: An introduction to psychological and physiological acoustics''. 2nd edition. New York and Basel: Marcel Dekker, Inc.</ref> The threshold of hearing is [[frequency]]-dependent and it has been shown that the ear's sensitivity is best at frequencies between 2&nbsp;kHz and 5&nbsp;kHz,<ref name="Johnson2015">{{cite book|last1=Johnson|first1=Keith|title=Acoustic and Auditory Phonetics|date=2015|publisher=Wiley-Blackwell|edition=third}}</ref> where the threshold reaches as low as −9&nbsp;dB SPL.<ref>{{Cite web|url=http://www.ucl.ac.uk/~smgxprj/public/askscience_v1_8.pdf|title=What's the quietest sound a human can hear?|last=Jones|first=Pete R|date=November 20, 2014|publisher=University College London|access-date=2016-03-16|quote=On the other hand, you can also see in Figure 1 that our hearing is slightly more sensitive to frequencies just above 1 kHz, where thresholds can be as low as −9 dBSPL!|archive-date=2016-03-24|archive-url=https://web.archive.org/web/20160324102019/http://www.ucl.ac.uk/~smgxprj/public/askscience_v1_8.pdf|url-status=dead}}</ref><ref>{{Cite web|url=http://www.feilding.net/sfuad/musi3012-01/html/lectures/007_hearing_II.htm|title=Lecture 007 Hearing II|last=Feilding|first=Charles|website=College of Santa Fe Auditory Theory|access-date=2016-03-17|quote=The peak sensitivities shown in this figure are equivalent to a sound pressure amplitude in the sound wave of 10 μPa or: about -6 dB(SPL). Note that this is for monaural listening to a sound presented at the front of the listener. For sounds presented on the listening side of the head there is a rise in peak sensitivity of about 6 dB [−12 dB SPL] due to the increase in pressure caused by reflection from the head.|archive-url=https://web.archive.org/web/20160507181640/http://www.feilding.net/sfuad/musi3012-01/html/lectures/007_hearing_II.htm|archive-date=2016-05-07|url-status=dead}}</ref><ref>{{Cite web|url=https://xiph.org/~xiphmont/demo/neil-young.html|title=24/192 Music Downloads ...and why they make no sense|last=Montgomery|first=Christopher|website=xiph.org|access-date=2016-03-17|quote=The very quietest perceptible sound is about -8dbSPL|archive-url=https://web.archive.org/web/20160314113111/https://xiph.org/~xiphmont/demo/neil-young.html|archive-date=2016-03-14|url-status=dead}}</ref>
[[File:Average click-evoked waveforms and Average hearing thresholds for younger and older adults.jpg|thumb|350x350px|Average hearing thresholds in [[decibel]]s&nbsp;(SPL) (the unit of 'dB(HL)' shown on the vertical axis is incorrect) are plotted from 125 to 8000 [[Hz]] for younger (18-30 year olds, red circles) and older adults (60-67 year olds, black diamonds). The hearing of older adults is shown to be significantly less sensitive than that of younger adults at frequencies of 4000 and 8000&nbsp;Hz, corresponding approximately to the [[Piano key frequencies|piano keys]] and tones of b′′′′ (B7) and b′′′′′ (B8), respectively. B8 is near the high end of the piano frequency range.]]