The Octatonic Scales
Octatonic scale
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The twelve tones of the chromatic scale partition into three non-overlapping diminished seventh chords. A combination of any two, omitting the third, forms an octatonic collection. As there are three diminished-seventh chords that can be omitted, it follows that there are only three distinct (non-transpositionally equivalent) diminished scales in the 12-tone system. Thus Olivier Messiaen considered it one of the modes of limited transposition. A given diminished scale has only two modes (one beginning its ascent with a whole step between its first two notes, while the other begins its ascent with a half step or semitone). T.
Each of the three distinct scales can form differently named scales with the same sequence of tones by starting at a different point in the scale. With alternative starting points listed in parentheses, the three are:
- E♭ diminished (F♯/G♭, A, C diminished): E♭, F, F♯, G♯, A, B, C, D, E♭
- D diminished (F, A♭, B diminished): D, E, F, G, A♭, B♭, B, C♯, D
- D♭ diminished (E, G, B♭ diminished): D♭, E♭, E, F♯, G, A, B♭, C, D♭
It may also be represented as 0134679t or labeled as set 8-28.
Among the collection's remarkable features is that it is the only collection that can be disassembled into four transpositionally-related pitch pairs in six different ways, each of which features a different interval class (Cohn). For example:
semitone: (C, C#), (D#, E) (F#, G), (A, Bb)
whole step: (C#,D#), (E, F#), (G, A), (Bb, C)
minor third:(C, Eb), (F#, A), (C#, E), (G, Bb)
major third:(C, E), (F#, Bb), (Eb, G), (A, C#)
perfect fourth: (C#, F#), (Bb,Eb), (G,C), (E,A)
tritone: (C, F#), (Eb,A), (C#,G), E, Bb)
