An open string left ringing against a fretted grip. Because it costs no finger, it sounds a note the closed shape has none left for -- a tension on top, or a pedal root underneath. Either a familiar grip with open strings added, or a shape so sparse the open strings carry the chord. These belong to their key rather than to a shape, so D, A, G and E have many and Eb a handful.
AbmMaj7b5 is Ab, Cb, D and G — Abm7b5 with the seventh raised a semitone.
It sounds brittle and impossible to mistake. Scarce enough that most players meet it as a passing sonority rather than as a chord they chose.

| Ab | Cb | D | G |
|---|---|---|---|
| 1 | ♭3 | ♭5 | 7 |
Rare tonic — a half-diminished chord with its seventh raised instead.
Also written AbmM7b5 or Abm(maj7)b5. The same chord either way; which spelling you meet depends on who wrote the chart.
An open string left ringing against a fretted grip. It costs no finger, so it can sound a note the closed shape has none left for: a tension on top, or a pedal root underneath.
These belong to their key rather than to a shape: they cannot be moved up the neck. D, A, G and E have many; E♭ has a handful.
AbmMaj7b5 has 6 of them, on strings 6-5-4-3-2-1, strings 6-4-3-2-1 and strings 5-4-3-2-1, from the 2nd fret up to the 5th — every inversion the chord has: Ab in the bass, Cb in the bass, Ebb in the bass and G in the bass. The one to learn first is the Cb shape at the 2nd fret, which is the easiest grip here.
Start with xx6787 — no barre. None of the shapes for AbmMaj7b5 uses an open string, so every one of them is movable; the lowest sits at the 3rd fret. 2 of the 5 need a barre. Together they cover the neck from the 3rd fret to the 12th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| 45x433 | 3rd fret | Ab, root position | G | all fretted |
| 4554x4 | 4th fret | Ab, root position | Ab | barred |
| xx6787 | 6th fret | Ab, root position | Cb | all fretted |
| x-11-x-12-12-10 | 10th fret | Ab, root position | D | all fretted |
| x-11-12-12-12-x | 11th fret | Ab, root position | Cb | barred |
The same notes rebuilt from scratch give 3 shell, 14 drop 2 and 10 drop 3 voicings, each on its own page.
Tensions. A shell of AbmMaj7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (Db) and the b13 (Fb).
Every note of AbmMaj7b5 is in Ab diminished.
Change one note of AbmMaj7b5 and you have Abdim (drop the major seventh), Abdim7 (the major seventh becomes a sixth), Abmaj7b5 (the minor third becomes a major third), Abm7b5 (the major seventh becomes a flat seventh) or AbmMaj7 (the flat fifth becomes a fifth).
AbmMaj7b5 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On AbmMaj7b5’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.