Perfect octave
Other names-
Interval class0
Just interval2:1[1]
Equal temperament1200[1]
24 equal temperament1200
Just intonation1200[1]
Layout of a musical keyboard (three octaves shown)
Perfect octave About this sound Play 
Multi-octave F major chord with octaves marked by brackets. About this sound Play full chord , About this sound lowest octave , About this sound middle octave , or About this sound highest octave .

In music, an octave (Latin: octavus: eighth) or perfect octave is the interval between one musical pitch and another with half or double its frequency. It is defined by ANSI[2] as the unit of frequency level when the base of the logarithm is two. 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".[3]

The most important musical scales are typically written using eight notes, and the interval between the first and last notes is an octave. For example, the C major scale is typically written C D E F G A B C, the initial and final Cs being an octave apart. Two notes separated by an octave have the same letter name and are of the same pitch class.

The interval between the first and second harmonics of the harmonic series is an octave.

The octave has occasionally been referred to as a diapason.[4]

To emphasize that it is one of the perfect intervals (including unison, perfect fourth, and perfect fifth), the octave is designated P8. The octave above or below an indicated note is sometimes abbreviated 8a or 8va (Italian: all'ottava), 8va bassa (Italian: all'ottava bassa, sometimes also 8vb), or simply 8 for the octave in the direction indicated by placing this mark above or below the staff.


An example of an octave, from G4 to G5

For example, if one note has a frequency of 440 Hz, the note one octave above is at 880 Hz, and the note one octave below is at 220 Hz. The ratio of frequencies of two notes an octave apart is therefore 2:1. Further octaves of a note occur at 2n times the frequency of that note (where n is an integer), such as 2, 4, 8, 16, etc. and the reciprocal of that series. For example, 55 Hz and 440 Hz are one and two octaves away from 110 Hz because they are ​12 (or 2−1) and 4 (or 22) times the frequency, respectively.

For Calculating the Octave Range between two given frequencies one has to simply enter :

Octave Range = log ( base 2 ) Higher Frequency / Lower Frequency

"Twinkle Twinkle Little Star" melody doubled in four octaves: consonant and equivalent. About this sound Play 

After the unison, the octave is the simplest interval in music. The human ear tends to hear both notes as being essentially "the same", due to closely related harmonics. Notes separated by an octave "ring" together, adding a pleasing sound to music. For this reason, notes an octave apart are given the same note name in the Western system of music notation—the name of a note an octave above A is also A. This is called octave equivalency, the assumption that pitches one or more octaves apart are musically equivalent in many ways, leading to the convention "that scales are uniquely defined by specifying the intervals within an octave".[5] The conceptualization of pitch as having two dimensions, pitch height (absolute frequency) and pitch class (relative position within the octave), inherently include octave circularity.[5] Thus all Cs, or all 1s (if C = 0), in any octave are part of the same pitch class.

Octave equivalency is a part of most "advanced musical cultures", but is far from universal in "primitive" and early music.[6][7] The languages in which the oldest extant written documents on tuning are written, Sumerian and Akkadian, have no known word for "octave". However, it is believed that a set of cuneiform tablets that collectively describe the tuning of a nine-stringed instrument, believed to be a Babylonian lyre, describe tunings for seven of the strings, with indications to tune the remaining two strings an octave from two of the seven tuned strings.[8] Leon Crickmore recently proposed that "The octave may not have been thought of as a unit in its own right, but rather by analogy like the first day of a new seven-day week".[9]

"Twinkle Twinkle Little Star" melody doubled at fifths: fairly consonant but not equivalent. About this sound Play 

Monkeys experience octave equivalency, and its biological basis apparently is an octave mapping of neurons in the auditory thalamus of the mammalian brain.[10] Studies have also shown the perception of octave equivalence in rats (Blackwell & Schlosberg 1943), human infants (Demany & Armand 1984),[11] and musicians (Allen 1967) but not starlings (Cynx 1993), 4–9 year old children (Sergeant 1983), or nonmusicians (Allen 1967).[5]

"Twinkle Twinkle Little Star" melody doubled at seconds: neither consonant nor equivalent. About this sound Play 

While octaves commonly refer to the perfect octave (P8), the interval of an octave in music theory encompasses chromatic alterations within the pitch class, meaning that G to G (13 semitones higher) is an Augmented octave (A8), and G to G (11 semitones higher) is a diminished octave (d8). The use of such intervals is rare, as there is frequently a preferable enharmonically-equivalent notation available (minor ninth and major seventh respectively), but these categories of octaves must be acknowledged in any full understanding of the role and meaning of octaves more generally in music.

Other Languages
العربية: جواب (موسيقى)
беларуская: Актава
беларуская (тарашкевіца)‎: Актава
български: Октава
čeština: Oktáva (hudba)
dansk: Oktav
Deutsch: Oktave
eesti: Oktav
Ελληνικά: Οκτάβα
español: Octava
Esperanto: Okto
فارسی: اکتاو
français: Octave (musique)
Frysk: Oktaaf
galego: Oitava
한국어: 옥타브
Հայերեն: Օկտավա
hrvatski: Oktava
Ido: Oktavo
Bahasa Indonesia: Oktaf
íslenska: Áttund
italiano: Ottava (musica)
עברית: אוקטבה
ქართული: ოქტავა
latviešu: Oktāva
lietuvių: Oktava
magyar: Oktáv
Nederlands: Octaaf (muziek)
日本語: オクターヴ
norsk: Oktav
norsk nynorsk: Oktav
oʻzbekcha/ўзбекча: Oktava
português: Oitava
română: Octavă
русский: Октава
Simple English: Octave
slovenčina: Hlasová oktáva
کوردی: ئۆکتەیڤ
српски / srpski: Октава (музика)
srpskohrvatski / српскохрватски: Oktava
suomi: Oktaavi
svenska: Oktav
Türkçe: Oktav
українська: Октава
Tiếng Việt: Quãng tám
中文: 八度