A7b9 guitar chord
The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped.
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About A7b9 — drop 3 voicings
A7b9 is A, C#, E, G and Bb — A9 with the ninth lowered a semitone.
It sounds dark and urgent. The flat ninth comes from the harmonic minor, so this is the V of a minor key rather than a major one.
A7b9 notes and formula
| A | C# | E | G | Bb |
|---|---|---|---|---|
| 1 | 3 | 5 | ♭7 | ♭9 |
Altered dominant — it points at a minor chord.
Also written A7(b9), A7-9 or A7♭9. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play A7b9
The same operation one voice further down: the third voice from the top falls an octave and becomes the bass.
That leaves a bigger hole under the top three notes, so a string gets skipped: the muted string in the middle is the shape, not a mistake.
A7b9 has 9 of them, on strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 13th — every inversion the chord has: A in the bass, C# in the bass, G in the bass and Bb in the bass. The one to learn first is the Bb shape at the nut.
5 of them sit on strings 5-3-2-1, so you can run the inversions up one set without changing strings — which is the whole reason to learn them as a family rather than as separate grips.
Start with x02323 — no barre and 1 open string. 1 of the 6 shapes here sits in open position. 2 of the 6 need a barre. Together they cover the neck from the 2nd fret to the 12th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x02323 | open position | A, root position | G | 1 open string |
| 5453xx | 3rd fret | A, root position | Bb | all fretted |
| xx5656 | 5th fret | G, 3rd inversion | Bb | all fretted |
| 575656 | 5th fret | A, root position | Bb | barred |
| xx7686 | 6th fret | A, root position | Bb | all fretted |
| x-12-11-12-11-12 | 11th fret | A, root position | E | barred |
The same notes rebuilt from scratch give 4 shell, 12 drop 2, 15 rootless and 4 open string voicings, each on its own page.
Tensions. A shell of A7b9, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (D#), the b13 (F) and the 13 (F#).
How to use A7b9
A7b9 is a dominant with its tension raised, so it still points at D — harder than a plain seventh does, because the altered tones sit a semitone from where they are going.
Voice by voice, A7b9 → Dm. 3 voices move by a semitone, and one note is common to both chords.
| In A7b9 | Moves | In Dm |
|---|---|---|
| A, the root | stays where it is | A, the fifth |
| C#, the major third | rises a semitone | D, the root |
| E, the fifth | rises a semitone | F, the minor third |
| G, the flat seventh | falls a whole tone | F, the minor third |
| Bb, the flat ninth | falls a semitone | A, the fifth |
What to play over A7b9
Every note of A7b9 is in A half-whole diminished.
Chords near A7b9
Change one note of A7b9 and you have A7 (drop the flat ninth), Aalt (the fifth becomes a sharp fifth), A9 (the flat ninth becomes a ninth), A7#9 (the flat ninth becomes a minor third) or A/G (drop the flat ninth).
A7b9 is an altered chord — a dominant seventh with its fifth or ninth moved. Altered dominant chords on every root.
On A7b9’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.