Dominant 7th b5 #9
7b5#9
0 - 4 - 6 - 10 - 15Dom7 with diminished 5th and augmented 9th
About Dominant 7th b5 #9
A dominant seventh flat five sharp nine chord lowers the fifth and raises the ninth — in C that is C, E, G♭, B♭ and D♯, written C7♭5♯9. It is one of the four fully altered dominants, and the one that keeps the blues clash of the raised ninth while giving up the anchor of a perfect fifth.
Notes and formula
The formula is 1 – 3 – ♭5 – ♭7 – ♯9, or 0 – 4 – 6 – 10 – 15 in semitones. Both altered notes move away from the natural ones in opposite directions.
Because the fifth is lowered rather than raised, the chord inherits the symmetry of a flat-five dominant: the tritone between C and G♭ splits the octave evenly, and the root becomes a matter of context.
How to play it
On guitar the movable form is x–3–4–3–4–x, sounding C–G♭–B♭–D♯. Everything essential is there and the third is dropped, which is acceptable here only because the raised ninth is doing similar work.
On piano keep C low, then E–B♭ as the defining pair, with G♭ and D♯ above. The chord is dense and only clear when the alterations sit on top.
How it differs from its neighbours
C7♯5♯9 raises both altered degrees and sounds emphatic and bright. This chord lowers the fifth instead, and the result is darker and less anchored.
C7♭5♭9 lowers both, and sounds closer to a diminished chord. Among the four combinations this one is the most ambiguous: a blues alteration on top of a symmetrical foundation.
Where it appears
In modern jazz comping, where a player reading 7alt chooses these particular alterations for voice-leading reasons rather than for colour.
It also arises from tritone substitution: play a dominant a tritone away with its own alterations, and the resulting notes over the original bass often spell exactly this chord.
Reading it in a chart
Charts rarely specify all of this. A symbol this precise usually means an arranger has voiced a section and wants that voicing, not a general instruction to alter.
In a small group the same bar would be written C7alt, and this chord would be one of several correct answers.
Scales that contain it
The altered scale contains every note and is the standard choice. The half–whole diminished scale contains the raised ninth and the lowered fifth but adds a natural thirteenth the chord does not want.
Whole tone contains the lowered fifth and nothing else useful here, so it fits only fragments of the chord.
Frequently asked questions
What notes are in a C7♭5♯9 chord?
C, E, G♭, B♭ and D♯. On guitar, x–3–4–3–4–x.
How is it different from 7♯5♯9?
The direction of the fifth. Lowered, the chord becomes symmetrical and loses its anchor; raised, it stays rooted and sounds brighter.
When would a chart specify this rather than 7alt?
When the voicing matters — in arranged music for a section. In a small group the same bar is normally written 7alt and left to the player.