Dominant 13th b9
13b9
0 - 4 - 7 - 10 - 13 - 21Dom13 with minor 9th
About Dominant 13th b9
A dominant thirteenth flat nine chord pairs a lowered ninth with a natural thirteenth — in C that is C, E, G, B♭, D♭ and A, written C13♭9. The combination looks contradictory on paper and is not: both notes belong to the half–whole diminished scale, and this chord is that scale's signature sonority.
Notes and formula
The formula is 1 – 3 – 5 – ♭7 – ♭9 – 13, or 0 – 4 – 7 – 10 – 13 – 21 in semitones. One altered note, one natural one, both above the seventh.
The pairing is what marks the chord out. The altered scale, which supplies most altered dominants, has no natural thirteenth — so a chord with both a flat nine and a natural thirteenth cannot come from it.
The scale it belongs to
The half–whole diminished scale alternates semitones and whole tones: C, D♭, E♭, E, F♯, G, A, B♭. It contains a major third, a flattened seventh, a lowered ninth and a natural thirteenth — precisely this chord.
It also supplies a raised ninth and a raised eleventh, which is why players over a 13♭9 often add notes that look like they belong to a different chord entirely. They belong to the same scale.
How to play it
On guitar the movable form is x–3–2–3–2–5, sounding C–E–B♭–D♭–A. Both colour notes are on top, which is where they have to be.
On piano the reliable voicing is C low, then E–B♭–D♭–A. Putting the flattened ninth below the seventh makes the chord sound like a mistake rather than a colour.
Where you hear it
In bebop and hard bop as a standard dominant, not a special effect. In big-band writing as the chord before a resolution to a major tonic, where the natural thirteenth softens the flat nine's severity.
It also appears in Brazilian and Latin jazz, where diminished-scale harmony over dominants is idiomatic.
Against 7♭9 and 13♯9
C7♭9 is the same alteration without the thirteenth: sharper, more classical. C13♯9 raises the ninth instead and sounds bluesy where this sounds urbane.
The natural thirteenth is what makes this chord sit comfortably in a full arrangement. A flat nine alone can dominate a texture; with a thirteenth above it, it does not.
Scales that contain it
The half–whole diminished scale, exactly. The altered scale does not fit — it has no natural thirteenth, and substituting it changes the chord.
This is one of the clearest cases in jazz where the chord symbol names the scale unambiguously, and reading it that way saves a great deal of thinking on the stand.
Frequently asked questions
What notes are in a C13♭9 chord?
C, E, G, B♭, D♭ and A. On guitar, x–3–2–3–2–5.
How can a chord have a flat nine and a natural thirteenth?
Because both belong to the half–whole diminished scale. The combination is impossible in the altered scale, which is what makes it a reliable signal of which scale to use.
Which scale should I play over it?
The half–whole diminished scale. The altered scale contains no natural thirteenth and will contradict the chord.