View source for Audio frequency

{{short description|Sound whose frequency is audible to the average human.}}

{{Sound measurements}}

An '''audio frequency''' or '''audible frequency''' ('''AF''') is a [[periodic function|periodic]] [[vibration]] whose [[frequency]] is [[human hearing range|audible to the average human]]. The [[International System of Units|SI unit]] of frequency is the [[hertz]] (Hz). It is the property of [[sound]] that most determines [[Pitch (music)|pitch]].<ref>{{Cite book|last1= Pilhofer |first1=Michael |title=Music Theory for Dummies|url=https://books.google.com/books?id=CxcviUw4KX8C|year=2007|publisher=For Dummies|page=97|isbn=9780470167946 }}</ref>

The generally accepted standard [[hearing range]] for humans is 20 to 20,000&nbsp;Hz.<ref>{{cite web|title=Hyperphysics|url=http://hyperphysics.phy-astr.gsu.edu/hbase/sound/earsens.html|access-date=19 September 2014}}</ref><ref>{{cite journal|last1=Heffner|first1=Henry|last2=Heffner|first2=Rickye|title=Hearing Ranges of Laboratory Animals|journal= Journal of the American Association for Laboratory Animal Science|date=January 2007|volume=46|issue=1|pages=20–2|pmid=17203911|url=http://www.ingentaconnect.com/content/aalas/jaalas/2007/00000046/00000001/art00003|access-date=19 September 2014}}</ref><ref>{{cite book|last=Rosen|first=Stuart|title=Signals and Systems for Speech and Hearing|date=2011|publisher=BRILL|page=163|edition=2nd|quote=For auditory signals and human listeners, the accepted range is 20Hz to 20kHz, the limits of human hearing}}</ref> In air at atmospheric pressure, these represent sound waves with [[wavelength]]s of {{convert|17|m|feet}} to {{convert|1.7|cm|inch}}. Frequencies below 20&nbsp;Hz are generally felt rather than heard, assuming the [[amplitude]] of the vibration is great enough. Sound frequencies above 20&nbsp;kHz are called [[ultrasonic]].

Sound propagates as mechanical vibration waves of pressure and displacement, in air or other substances.<ref>{{cite web |title=Definition of SOUND |url=http://www.merriam-webster.com/dictionary/sound |access-date=3 October 2016}}</ref> In general, frequency components of a sound determine its "color", its [[timbre]]. When speaking about the frequency (in singular) of a sound, it means the property that most determines its [[Pitch (music)|pitch]].<ref>{{Cite book |last1=Pilhofer |first1=Michael |url=https://books.google.com/books?id=CxcviUw4KX8C |title=Music Theory for Dummies |publisher=For Dummies |year=2007 |isbn=978-0-470-16794-6 |page=97}}</ref> Higher pitches have higher frequency, and lower pitches are lower frequency. 

The frequencies an ear can hear are limited to a [[Threshold of hearing|specific range of frequencies]].  The [[audible frequency]] range for humans is typically given as being between about 20&nbsp;Hz and 20,000&nbsp;Hz (20&nbsp;kHz), though the high frequency limit usually reduces with age. Other [[species]] have different hearing ranges. For example, some dog breeds can perceive vibrations up to 60,000&nbsp;Hz.<ref name="Physics Factbook">{{cite web |last=Condon |first=Tim |year=2003 |editor-last=Elert |editor-first=Glenn |title=Frequency range of dog hearing |url=https://hypertextbook.com/facts/2003/TimCondon.shtml |accessdate=2008-10-22 |website=The Physics Factbook}}</ref> 

In many media, such as air, the [[speed of sound]] is approximately independent of frequency, so the wavelength of the sound waves (distance between repetitions) is approximately inversely proportional to frequency.

==Frequencies and descriptions==
{| class="wikitable"
! Frequency (Hz)
! [[Octave]]
! Description
|-
| 16 to 32
| 1st
| The lower human threshold of hearing, and the lowest pedal notes of a pipe organ.
|-
| 32 to 512
| 2nd to 5th
| Rhythm frequencies, where the lower and upper bass notes lie.
|-
| 512 to 2,048
| 6th to 7th
| Defines human [[Intelligibility (communication)|speech intelligibility]], gives a horn-like or tinny quality to sound.
|-
| 2,048 to 8,192
| 8th to 9th
| Gives presence to speech, where [[Labial consonant|labial]] and [[Fricative consonant|fricative]] sounds lie.
|-
| 8,192 to 16,384
| 10th
| Brilliance, the sounds of bells and the ringing of cymbals and [[sibilance]] in speech.
|-
| 16,384 to 32,768
| 11th
| Beyond brilliance, nebulous sounds approaching and just passing the upper human threshold of hearing
|}
[[File:Middle C, or 262 hertz, on a virtual oscilloscope.png|thumb|[[Oscilloscope|Oscillogram]] of a [[pure tone]] [[C (musical note)|middle C]] (262 Hz). (Scale: 1 square is equal to 1 [[millisecond]])]]
[[File:C5 523 Hz oscillogram.png|thumb|C5, an octave above middle C. The frequency is twice that of middle C (523 Hz).]]
[[File:C3 131 Hz oscillogram.png|thumb|C3, an octave below middle C. The frequency is half that of middle C (131 Hz).]]
{| class="wikitable"
! MIDI note
! Frequency (Hz)
! Description
! Sound file
|-
| 0
| 8.17578125
| Lowest [[Organ (music)|organ]] note
| n/a ([[fundamental frequency]] inaudible)
|-
| 12
| 16.3515625
| Lowest note for tuba, large pipe organs, [[Bösendorfer]] Imperial grand piano
| n/a ([[fundamental frequency]] inaudible under average conditions)
|-
| 24
| 32.703125
| Lowest C on a standard 88-key [[piano]]
| [[File:Audio Frequency tone, C1, 32.70hz.ogg]]
|-
| 36
| 65.40625
| Lowest note for [[cello]]
| [[File:Audio frequency tone, C2, 65.41hz.ogg]]
|-
| 48
| 130.8125
| Lowest note for [[viola]], [[mandola]]
| [[File:Audio frequency tone, C3, 130.81hz.ogg]]
|-
| 60
| 261.625
| [[Middle C]]
| [[File:Audio Frequency tone, Middle C, C4, 261.63hz.ogg]]
|-
| 72
| 523.25
| C in middle of [[Clef#Treble clef|treble clef]]
| [[File:Audio Frequency tone, C5, 523.25hz.ogg]]
|-
| 84
| 1,046.5
| Approximately the highest note reproducible by the average female [[human voice]]
| [[File:Audio Frequency tone, C6, 1046.50hz.ogg]]
|-
| 96
| 2,093
| Highest note for a [[flute]]
| [[File:Audio Frequency tone, C7, 2093hz.ogg]]
|-
| 108
| 4,186
| Highest note on a standard 88-key piano
| [[File:Audio frequency tone, C8, 4186hz.ogg]]
|-
| 120
| 8,372
|
| [[File:Audio frequency tone, C9, 8372hz.ogg]]
|-
| 132
| 16,744
| Approximately the tone that a typical [[Cathode ray tube|CRT]] [[television]] emits while running.
| [[File:Audio frequency tone, C10, 16744hz.ogg]]
|}

==See also==
*[[Absolute threshold of hearing]]
*[[Hypersonic effect]], controversial claim for human perception above 20,000&nbsp;Hz
*[[Loudspeaker]]
*[[Musical acoustics]]
*[[Piano key frequencies]]
*[[Scientific pitch notation]]
*[[Whistle register]]

==References==
{{Reflist}}

{{Authority control}}

[[Category:Acoustics]]
[[Category:Sound]]
[[Category:Sound measurements]]
[[Category:Physical quantities]]
[[Category:Audio engineering]]