In classical music from Western culture, a diminished octave ( Play (help·info)) is an interval produced by narrowing a perfect octave by a chromatic semitone. 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 C♯4 to C5, and from C4 to C♭5 are diminished octaves, spanning eleven semitones. Being diminished, it is considered a dissonant interval.
The diminished octave is enharmonically equivalent to the major seventh.
- ^ a b 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.
- ^ Benward & Saker (2003), p.92.