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In musical set theory, an interval class (often abbreviated: ic), also known as unordered pitch-class interval, interval distance, undirected interval, or "(even completely incorrectly) as 'interval mod 6'" (Rahn 1980, 29; Whittall 2008, 273–74), is the shortest distance in pitch class space between two unordered pitch classes. For example, the interval class between pitch classes 4 and 9 is 5 because 9 − 4 = 5 is less than 4 − 9 = −5 ≡ 7 (mod 12). See modular arithmetic for more on modulo 12. The largest interval class is 6 since any greater interval ''n'' may be reduced to 12 − ''n''. == Use of interval classes == The concept of interval class accounts for octave, enharmonic, and inversional equivalency. Consider, for instance, the following passage: (To hear a MIDI realization, click the following: In the example above, all four labeled pitch-pairs, or dyads, share a common "intervallic color." In atonal theory, this similarity is denoted by interval class—ic 5, in this case. Tonal theory, however, classifies the four intervals differently: interval 1 as perfect fifth; 2, perfect twelfth; 3, diminished sixth; and 4, perfect fourth. Incidentally, the example's pitch collection forms an octatonic set. Note: in the excerpt above, the fifth note should be notated as an F-sharp, not an F-flat. The MIDI recording plays the correct note, however. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Interval class」の詳細全文を読む スポンサード リンク
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