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.
Abmaj7b5 is Ab, C, D and G — Abmaj7 with the fifth lowered a semitone.
It sounds hollow and hard to place. Far more often met spelled the other way round, as a ♯11 over a chord that kept its fifth.

| Ab | C | D | G |
|---|---|---|---|
| 1 | 3 | ♭5 | 7 |
Coloured tonic — rare, and unstable for a major chord.
Also written AbM7b5, AbΔ7b5 or Abmaj7(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.
Abmaj7b5 has 2 of them, only on the bottom four strings, all of them at the 3rd fret — every inversion the chord has: Ab in the bass and G in the bass. The one to learn first is the Ab shape at the 3rd fret, which is the easiest grip here.
Start with xx6788 — no barre. None of the shapes for Abmaj7b5 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 13th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| 435533 | 3rd fret | Ab, root position | G | barred |
| 4555x4 | 4th fret | Ab, root position | Ab | barred |
| xx6788 | 6th fret | Ab, root position | C | all fretted |
| x-11-10-12-13-10 | 10th fret | Ab, root position | D | all fretted |
| x-11-12-12-13-x | 11th fret | Ab, root position | C | all fretted |
The same notes rebuilt from scratch give 5 shell, 14 drop 2 and 10 drop 3 voicings, each on its own page.
Tensions. A shell of Abmaj7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (Bb) and the 13 (F).
How you get to it. The turn that lands on Abmaj7b5 is Bbm7 to Eb7 — the ii and the V of Ab — and Eb7 shares its third and seventh with Bbm7, so the hand barely moves between them.
In which keys. Every note of Abmaj7b5 belongs to C minor (the ♭VI) and Eb major (the IV, the subdominant).
Every note of Abmaj7b5 is in Ab lydian.
Change one note of Abmaj7b5 and you have Abmaj7 (the flat fifth becomes a fifth), Abmaj7#5 (the flat fifth becomes a sharp fifth), AbmMaj7b5 (the major third becomes a minor third) or Ab7b5 (the major seventh becomes a flat seventh).
Abmaj7b5 is a major chord — root, major third, fifth. Major chords on every root.
On Abmaj7b5’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.