In music, an octave () is the interval between one musical pitch and another with half or double its frequency. 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." It may be derived from the harmonic series as the interval between the first and second harmonics.

The octave has occasionally been referred to as a diapason.

The octave above an indicated note is sometimes abbreviated 8va, and the octave below 8vb. To emphasize that it is one of the perfect intervals, the octave is sometimes designated P8; the other perfect intervals, the unison, perfect fourth, and perfect fifth, are designated PU (or P1), P4, and P5.

Theory

For example, if one note has a frequency of 400 Hz, the note an octave above it is at 800 Hz, and the note an octave below is at 200 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, 50 Hz and 400 Hz are one and two octaves away from 100 Hz because they are ½ (or 2 ⁻¹) and 4 (or 2²) times the frequency, respectively.

" melody doubled in four octaves: consonant and equivalent. ]]

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 in 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". The conceptualization of pitch as having two dimensions, pitch height (absolute frequency) and pitch class (relative position within the octave), inherently include octave circularity. 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.

" melody doubled at fifths: fairly consonant but not equivalent. ]]

Monkeys experience octave equivalency, and its biological basis apparently is an octave mapping of neurons in the auditory thalamus of the mammalian brain and the perception of octave equivalency in self-organizing neural networks can form through exposure to pitched notes, without any tutoring, this being derived from the acoustical structure of those notes. Studies have also shown the perception of octave equivalence in rats (Blackwell & Schlosberg, 1943), human infants (Demany & Armand, 1984), and musicians (Allen, 1967) but not starlings (Cynx, 1993), 4-9 year old children (Sergeant, 1983), or nonmusicians (Allen, 1967).

" melody doubled at seconds: neither consonant nor equivalent. ]]

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 to G♯ (13 semitones higher) is an augmented octave (A8), and to G♭ (11 semitones higher) is a diminished octave (d8). The use of such intervals is rare, as there is frequently a more preferable enharmonic notation available, but these categories of octaves must be acknowledged in any full understanding of the role and meaning of octaves more generally in music.

Other uses of term

In terms of playing an instrument, "octave" may also mean a special effect involving playing two notes an octave apart at the same time. Some instruments innately provide octaves by having double strings, reeds, etc.—as in the twelve-string guitar or octave harmonica.

Most classical music systems divide the octave into 12 semitones (see musical tuning). These semitones are usually equally spaced in frequency, in a method called equal temperament.

==Notation==

The notation 8va is sometimes seen in sheet music, meaning "play this an octave higher than written." (all' ottava: "at the octave") 8va stands for ottava, the Italian word for octave (note the 8 and the word 'oct'). Sometimes 8va also tell the musician to play a passage an octave lower, though the similar notation 8vb (ottava bassa) is more common. Similarly, 15ma (quindicesima) means "play two octaves higher than written" and 15mb (quindicesima bassa) means "play two octaves lower than written." Col 8 or c. 8va stands for coll'ottava and means "play the notes in the passage together with the notes in the notated octaves". Any of these directions can be cancelled with the word loco, but often a dashed line or bracket indicates the extent of the music affected.

For music-theoretical purposes (not on sheet music), octave can be abbreviated as P8 (which is an abbreviation for Perfect Eighth, the interval between 12 semitones or an octave).

See also

References

External links

Category:Superparticular intervals