Editing Octave (section)

{{Short description|Interval between one musical pitch and another with double its frequency}}
{{Other uses}}
{{Image frame|content=<score lang="lilypond"> {
\override Score.TimeSignature#'stencil = ##f
\relative c' {
   \clef treble 
   \time 4/4
   \key c \major
   <c c'>1
} }
</score>|width=120|caption=A perfect octave between two Cs}}

{{Infobox Interval
| main_interval_name = Perfect octave
| inverse = [[unison]]
| complement = octave
| other_names = -
| abbreviation = P8
| semitones = 12
| interval_class = 0
| just_interval = 2:1<ref name="Duffin" />
| cents_equal_temperament = 1200<ref name="Duffin">{{cite book|last1=Duffin|first1=Ross W.|title=How equal temperament ruined harmony : (and why you should care)|date=2008|publisher=W. W. Norton|location=New York|isbn=978-0-393-33420-3|page=163|edition=First published as a Norton paperback.|url=https://books.google.com/books?id=i5LC7Csnw7UC&q=how+equal+temperament+ruined+harmony|access-date=28 June 2017|language=en|url-status=live|archive-url=https://web.archive.org/web/20171205150905/https://books.google.com/books?id=i5LC7Csnw7UC&printsec=frontcover&dq=how+equal+temperament+ruined+harmony&hl=en&sa=X&ved=0ahUKEwiHl-v79eDUAhVOID4KHVp8D4cQ6AEIJjAA|archive-date=5 December 2017}}</ref>
| cents_24T_equal_temperament = 
| cents_just_intonation = 1200<ref name="Duffin" />
}}
In [[music]], an '''octave''' ({{langx|la|octavus|link=no}}: eighth) or '''perfect octave''' (sometimes called the [[Pythagorean interval|'''diapason''']])<ref>{{cite book|url=https://books.google.com/books?id=1LIPFk6oFVkC&q=diatessaron+diapason+diapente+fourth+fifth&pg=PA550|title=A Dictionary of Christian Antiquities|author=William Smith|author2=Samuel Cheetham|location=London|publisher=John Murray|year=1875|isbn=9780790582290|archive-url=https://web.archive.org/web/20160430185327/https://books.google.com/books?id=1LIPFk6oFVkC&pg=PA550&dq=diatessaron+diapason+diapente+fourth+fifth|archive-date=2016-04-30|url-status=live|name-list-style=amp}}</ref> is an [[Interval (music)|interval]] between two notes, one having twice the [[frequency]] of vibration of the other. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems".<ref>Cooper, Paul (1973). ''Perspectives in Music Theory: An Historical-Analytical Approach'', p. 16. {{ISBN|0-396-06752-2}}.</ref> The interval between the first and second harmonics of the [[Harmonic series (music)|harmonic series]] is an octave. In Western [[Musical notation|music notation]], notes separated by an octave (or multiple octaves) have the same [[Musical note#Written notes|name]] and are of the same [[pitch class]].

To emphasize that it is one of the [[interval (music)#Perfect|perfect intervals]] (including [[unison]], [[perfect fourth]], and [[perfect fifth]]), the octave is designated P8. Other [[Interval quality|interval qualities]] are also possible, though rare. The octave above or below an indicated [[musical note|note]] is sometimes abbreviated ''8<sup>a</sup>'' or ''8<sup>va</sup>'' ({{langx|it|all'ottava}}), ''8<sup>va</sup> bassa'' ({{langx|it|all'ottava bassa}}, sometimes also ''8<sup>vb</sup>''), or simply ''8'' for the octave in the direction indicated by placing this mark above or below the staff.