Fig. 1 · Eb to Bbb

interval

E♭ diminished fifth

E♭lowerB♭♭upperd56 half steps

A perfect fifth narrowed by a half step. The interval inside every diminished triad.

On the keyboard

Fig. 2

What is true of it

E♭ up a diminished fifth is B♭♭: 6 half steps, and 5 letters counting both ends.

Turn it upside down — put the E♭ on top — and it becomes a augmented fourth. The two numbers always add to nine, and the two sizes to twelve.

It is a dissonance.

Six half steps can be written two ways: E♭ to A is a fourth, E♭ to B♭♭ is a fifth. They sound the same and behave differently.

Every interval on E♭

E♭ → F♭minor second · dissonance E♭ → Fmajor second · dissonance E♭ → G♭minor third · imperfect consonance E♭ → Gmajor third · imperfect consonance E♭ → A♭perfect fourth · perfect consonance E♭ → Aaugmented fourth · dissonance E♭ → B♭perfect fifth · perfect consonance E♭ → C♭minor sixth · imperfect consonance E♭ → Cmajor sixth · imperfect consonance E♭ → D♭minor seventh · dissonance E♭ → Dmajor seventh · dissonance

C d5 C♯ d5 D♭ d5 D d5 E d5 F d5 F♯ d5 G♭ d5 all 204