Frequency

=== Sound ===
{{main article|Audio frequency}}
[[File:Ultrasound range diagram.svg|thumb|upright=1.7|The [[sound wave]] spectrum, with rough guide of some applications]]

Sound propagates as mechanical vibration waves of pressure and displacement, in air or other substances.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/sound|title=Definition of 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 |title=Music Theory for Dummies|url=https://books.google.com/books?id=CxcviUw4KX8C|year=2007|publisher=For Dummies|page=97|isbn= 978-0-470-16794-6}}</ref>

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
| url=https://hypertextbook.com/facts/2003/TimCondon.shtml
| title=Frequency range of dog hearing
| first=Tim
| last=Condon
| year=2003
| website=The Physics Factbook
| editor-last=Elert
| editor-first=Glenn
| accessdate=2008-10-22
}}</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.