Diminished octave

diminished octave
Inverse Augmented unison
Other names Diminished eighth
Abbreviation d8[1]
Semitones 11
Interval class 1
Just interval 48:25
Equal temperament 1100
24 equal temperament 1100
Just intonation 1129
Diminished octave on C  Play .
Diminished octave on C-sharp  Play .

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.[2]

The diminished octave is enharmonically equivalent to the major seventh.


  1. 1 2 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. Benward & Saker (2003), p.92.
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