Augmented octave

In Western tonal music theory, an augmented octave is the sum of a perfect octave and an augmented unison or chromatic semitone. It is the interval between two notes, with the same note letter on staff positions an octave apart, whose alterations cause them, in ordinary equal temperament, to be thirteen semitones apart. In other words, it is a perfect octave which has been widened by a half-step, such as B♭ and B♮ or C and C♯; it is a compound augmented unison. It is the enharmonic equivalent of a minor ninth.^[1]

Augmented octave

Inverse	see "Augmented unison"
Name
Other names	Augmented eighth
Abbreviation	A8
Size
Semitones	13
Interval class	1
Just interval	25:12
Cents
12-Tone equal temperament	1300
Just intonation	1271

Augmented octave on C. Play^ⓘ

See also

• False relation
• List of musical intervals
• List of pitch intervals
• Ninth § Minor ninth