A musical ratio of 48:25. Same as Diminished Eighth.

In classical music from Western culture, a diminished octave 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 C4 to C5, and from C4 to C5 are diminished octaves, spanning eleven semitones. Being diminished, it is considered a dissonant interval.

The diminished octave is enharmonically equivalent to the major seventh. Wikipedia, Diminished Octave

See Also

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B Flat 3rd Octave
C 1st Octave
D 2nd Octave
Diminished
diminished seventh
E Sharp 3rd Octave
Figure 1.8 - Electromagnetic Scale in Octaves
Figure 11.01 - Octave composed of Equal Thirds and Triads
Figure 12.11 - Russells Locked Potential Full Ten Octave Gamut
Figure 12.12 - Russells Multiple Octave Waves as Fibonacci Spirals
Figure 12.12 - Russells Multiple Octave Waves as Fibonacci Spirals - See Also
Figure 17.03 - Analysis of the Octave Gravity Bar
Figure 7B.10 - Russells Periodic Chart of the first four octaves of proto-matter
Figure 9.16 - Russells 1-4 Octaves of Matter as Integrated Light - The Universal Constant
Figure 9.17 - Russells Ten Octaves of Matter as Integrated Light - The Universal Constant
Interval
Law of Octave
Octave
Major Seventh
Minor Seventh
Octave Relationships
RULE OF THE OCTAVE
Scale of the Forces in Octaves
Seventh
The Russell Nine Octave Chart of the Elements
11.15 - Indig Numbers - Inert Gases and Octave Position
12.17 - Note about Octave Relationships in Russells System
12.18 - Multiple Octave Progression