Abmadd9 is Ab, Cb, Eb and Bb — Abm with the ninth added, and no seventh.
It sounds sharp-edged. The ninth grinding a whole step under the minor third is the edge an m9 softens.

| Ab | Cb | Eb | Bb |
|---|---|---|---|
| 1 | ♭3 | 5 | 9 |
Minor tonic — a triad with one colour on it.
Also written Abm(add9), Abmin(add9) or Ab-add9. The same chord either way; which spelling you meet depends on who wrote the chart.
Abmadd9 in 1st inversion puts Cb in the bass instead of Ab, the 3rd of the chord. The notes are the same; what changes is what the bass line does, which is most of why you would reach for it — it lets the lowest voice move by step where the root would have jumped.
2 of Abmadd9’s 7 common shapes do this: xx9896, x-14-13-13-11-x.
Start with 42x34x — no barre and down at the nut. None of the shapes for Abmadd9 uses an open string, so every one of them is movable; the lowest sits at the 2nd fret. 2 of the 7 need a barre. Together they cover the neck from the 2nd fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| 42x34x | 2nd fret | Ab, root position | Eb | all fretted |
| 466446 | 4th fret | Ab, root position | Bb | barred |
| xx6446 | 4th fret | Ab, root position | Bb | all fretted |
| xx9896 | 6th fret | Cb, 1st inversion | Bb | all fretted |
| x-11-9-8-11-x | 8th fret | Ab, root position | Bb | all fretted |
| x-11-9-x-11-11 | 9th fret | Ab, root position | Eb | barred |
| x-14-13-13-11-x | 11th fret | Cb, 1st inversion | Bb | all fretted |
The same notes rebuilt from scratch give 13 drop 2 and 8 drop 3 voicings, each on its own page.
How you get to it. The turn that lands on Abmadd9 is Bbm7♭5 to Eb7♭9: the ii and the V of Ab minor, which is where a minor tonic is usually arrived at rather than simply begun on.
In which keys. Every note of Abmadd9 belongs to Eb minor (the iv, the subdominant), F# major (the ii, the supertonic), Ab minor (the i, the tonic) and B major (the vi, the submediant).
Every note of Abmadd9 is in Ab dorian, Ab natural minor, Ab harmonic minor and Ab melodic minor.
Change one note of Abmadd9 and you have Abm (drop the ninth), Absus2 (drop the minor third), Abm6 (the ninth becomes a sixth), Abm69 (add the sixth), Abm7 (the ninth becomes a flat seventh) or Abm9 (add the flat seventh).
Abmadd9 is a minor chord — root, minor third, fifth. Minor chords on every root.
On Abmadd9’s sound and use this page follows Robert Rawlins & Nor Eddine Bahha, Jazzology (Hal Leonard, 2005). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.