How many semitones is a diminished ninth?

A Diminished Ninth spans 12 semitones: C – Dbb. Count the semitones of any interval with the interval calculator.

Is a diminished ninth the same as an octave?

In equal temperament the two sound identical. The spelling marks the upper note as a lowered ninth degree rather than the root repeated.

What is a compound interval?

Any interval wider than an octave. A Diminished Ninth is an octave plus a diminished second, and it keeps the character of that simple interval in a more open, less congested form.

How do I play Diminished Ninth?

On guitar the handiest shape is Next string, B 1 · E 8, read as string and fret; the instrument panel draws it from any starting note with the other shapes. On the piano count 12 semitones up from any key, black keys included. Play the notes together for the harmonic form, one after the other for the melodic form.

What is the inversion of Diminished Ninth?

The inversion of Diminished Ninth is the Augmented Seventh: put the lower note an octave higher and the distance that remains is the inversion. The two always add up to an octave, 12 semitones and 12 semitones, and swap their qualities between major and minor, or keep perfect as perfect.

Diminished Ninth Interval: How It Sounds, with Song Examples

Play it on your instrument

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From

On the piano, from every note

From	Notes	Play it on your instrument
C	C – Dbb
C#	C# – Db
D	D – Ebb
Eb	Eb – Fbb
E	E – Fb
F	F – Gbb
F#	F# – Gb
G	G – Abb
Ab	Ab – Bbbb
A	A – Bbb
Bb	Bb – Cbb
B	B – Cb

Tap a key or a fret to hear it.

Number and quality

An interval has two names. The number counts the letter names from the lower note to the upper one, and the quality counts the semitones inside that number. Diminished Ninth spans 9 letter names, which makes it a ninth, and 12 semitones, which makes it diminished.

DLetter
ELetter
FLetter
GLetter
ALetter
BLetter
CLetter
12 semitones

Read on: number and quality · inversion · compound intervals · consonance and dissonance

Every ninth

A ninth can take these qualities, one semitone apart; choose one to see the upper note move and hear the pair.

Where it lives

Diminished Ninth is in every chord whose formula includes 9d from the root, in every scale that includes it from the tonic, and between these pairs of notes in a major key.

Related intervals

The intervals one step from Diminished Ninth: its inversion, the same sound spelled differently, its simple or compound form, and its nearest neighbours in size.

Augmented Seventh7A · 12 semitones · C – B#
Inversion: together they make an octave
Major Seventh7M · 11 semitones · C – B
One size away
Minor Ninth9m · 13 semitones · C – Db
One size away

Open it in a tool

Understanding Diminished Ninth

Names and symbols

Diminished Ninth is written d9, 9d: the letter is the quality, the number the size. Chord formulas on this site write the number first, as tonal does.

The octave is the one interval every tradition names the same way. An augmented seventh and a diminished ninth sound exactly like it and are written only when the spelling of a chord or a line demands them.

How it sounds

A Diminished Ninth spans 12 semitones: C – Dbb. It is an octave plus a diminished second, and compound intervals keep the quality of the simple interval inside them while losing much of its edge — the extra octave gives the two notes room to stop interfering with each other.

It measures the same as an octave, since the diminished second it is built from spans no distance in equal temperament.

How it is used

It is almost purely notational, appearing where a chromatically lowered ninth has to keep its letter name.

Learn this properly

Chapter 5: Intervals

Common questions

How many semitones is a diminished ninth?: A Diminished Ninth spans 12 semitones: C – Dbb. Count the semitones of any interval with the interval calculator.
Is a diminished ninth the same as an octave?: In equal temperament the two sound identical. The spelling marks the upper note as a lowered ninth degree rather than the root repeated.
What is a compound interval?: Any interval wider than an octave. A Diminished Ninth is an octave plus a diminished second, and it keeps the character of that simple interval in a more open, less congested form.
How do I play Diminished Ninth?: On guitar the handiest shape is Next string, B 1 · E 8, read as string and fret; the instrument panel draws it from any starting note with the other shapes. On the piano count 12 semitones up from any key, black keys included. Play the notes together for the harmonic form, one after the other for the melodic form.
What is the inversion of Diminished Ninth?: The inversion of Diminished Ninth is the Augmented Seventh: put the lower note an octave higher and the distance that remains is the inversion. The two always add up to an octave, 12 semitones and 12 semitones, and swap their qualities between major and minor, or keep perfect as perfect.