八度

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在音樂中，一個八度（有時略作8ve或8va）是一種音程，也就是2個不同音高的音符之音高差異或音高距離。這種名為八度的音高差異，對應於頻率的差異，並非一個固定的赫茲數，而是一個固定的頻率比率，該比率為2：1。舉例而言，鋼琴中央A音高對應之頻率為440赫茲，其高八度之A音對應之頻率為880赫茲；其低八度之A音對應之頻率則為220赫茲。

八度是和聲學中第二簡單的音程關係（最簡單的是完全一度）。由於人耳在聽到八度和聲時，有將兩個音當成同一個音的傾向；因此，音程差為八度的兩音在西方音樂記譜法中有相同的音名。這個「音程差為八度的兩音有相同音名」的關係稱作等價八度（octave equivalence）

, and is closely related to the concept of harmonics.  This is similar to enharmonic equivalency, and less so transpositional equivalency and, less still, inversional equivalency, the latter two of which are generally used only in musical set theory or atonal theory. Thus all C#s, or all 1s (if C=0), in any octave are part of the same pitch class. Octave equivalency is a part of most musics, but is far from universal in "primitive" and early music (e.g., Nettl, 1956; Sachs & Kunst, 1962).

As well as being used to describe the relationship between two notes, the word is also used when speaking of a range of notes that fall between a pair an octave apart. In the diatonic scale, this is 8 notes if one counts both ends, hence the name "octave", from Italian for 8. In the chromatic scale, this is 13 notes counting both ends, although traditionally, one speaks of 12 notes of the chromatic scale, not counting both ends. Other scales may have a different number of notes covering the range of an octave, but the word "octave" is still used.

In most Western music, the octave is divided into 12 semitones (see musical tuning). These semitones are usually equally spaced out in a method known as equal temperament.

The notation 8va is sometimes seen in sheet music, meaning "play this an octave higher than written." 8va stands for ottava, the Italian word for octave. Sometimes 8va will also be used to indicate a passage is to be played an octave lower, although the similar notation 8vb (ottava bassa) is more common. Similarly, 15ma (quindicesima) means "play two octaves higher than written." Coll'ottava means to play the passage in 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.

[编辑] See also

Solfege
diapason
cent (music)

Octave
# semitones	Interval class	# cents in equal temperament	Most common diatonic name	Comparable just interval	# cents in just interval	Just interval vs. equal-tempered interval
12	0	1200	perfect octave	2:1	1200	0
Template:Diatonic intervals

[编辑] Source

Burns, Edward M. (1999). "Intervals, Scales, and Tuning", The Psychology of Music second edition. Deutsch, Diana, ed. San Diego: Academic Press. ISBN 0122135644.
- Sachs, C. and Kunst, J. (1962). In The wellsprings of music, ed. Kunst, J. The Hague: Marinus Nijhoff.