{{short description|Sound whose frequency is audible to the average human}}
{{Sound measurements}}
An '''audio frequency''' or '''audible frequency''' ('''AF''') is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines 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 Hz (20 kHz).<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 wavelengths of {{convert|17|m|feet}} to {{convert|1.7|cm|inch}}. Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough. Sound waves that have frequencies below 20 Hz are called infrasonic and those above 20 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.<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 have lower frequency.
The frequencies an ear can hear are limited to a specific range of frequencies. The audible frequency range for humans is typically given as being between about 20 Hz and 20,000 Hz (20 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 Hz (60 kHz).<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 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 and 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|Oscillogram of a pure tone middle C (262 Hz). (Scale: 1 square is equal to 1 millisecond)]] thumb|C5, an octave above middle C. The frequency is twice that of middle C (523 Hz). 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 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 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 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 Hz *Loudspeaker *Musical acoustics *Piano key frequencies *Scientific pitch notation *Whistle register
==References== {{Reflist}}
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Category:Acoustics Category:Sound Category:Sound measurements Category:Physical quantities Category:Audio engineering