Diminished octave

In classical music from Western culture, a diminished octave (Play ) is an interval produced by narrowing a perfect octave by a chromatic semitone.[1] As such, the two notes are denoted by the same letter but have different accidentals. For instance, the interval from C4 to C5 is a perfect octave, twelve semitones wide, and both the intervals from C4 to C5 and from C4 to C5 are diminished octaves, spanning eleven semitones. Being diminished, it is considered a dissonant interval.[3]

diminished octave
InverseAugmented unison
Other namesDiminished eighth
Interval class1
Just interval48:25, 256:135[2], 4096:2187
Equal temperament1100[2]
24 equal temperament1100
Just intonation1129, 1108[2], 1086

The diminished octave is enharmonically equivalent to the major seventh.


  1. Benward & Saker (2003). Music: In Theory and Practice, Vol. I, p.54. ISBN 978-0-07-294262-0. Specific example of an d8 not given but general example of perfect intervals described.
  2. Duffin, Ross W. (2008). How equal temperament ruined harmony : (and why you should care) (First published as a Norton paperback. ed.). New York: W. W. Norton. p. 163. ISBN 978-0-393-33420-3. Retrieved 28 June 2017.
  3. Benward & Saker (2003), p.92.
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