Ab7sus4 is Ab, Db, Eb and Gb — with the third replaced by the fourth.
It sounds leaning rather than shoving. It keeps the flat seventh’s pull and loses the tritone, so it moves without making a hard cadence.
Dominant — it points a fifth down, but softly.
Also written Ab7sus or Ab dominant 7 sus 4.
Ab7sus4 is a dominant with a fourth where the third would be. In older styles the fourth falls a half step and the chord becomes Ab7; in modern jazz it often stays, and the sus chord resolves to Dbmaj7 as it is.
Listen for: The fourth falls a half step to the third, which holds over the barline as the major seventh of the I.
Put Ebm7 over the root of the V and you have Ab7sus4: a ii–V in a single chord. That’s why one sus chord can stand in for a bar of ii and a bar of V.
Listen for: The upper notes don’t change from the ii to the sus chord. Only the bass moves, to the root of the V.
A tune can be built from nothing but sus chords, with the fourth never resolving.
Heard in “Maiden Voyage”
In which keys. Every note of Ab7sus4 belongs to C# major, C# minor, Eb minor, E major, F# major, Ab minor, Bb minor and B major.
Every note of Ab7sus4 is in Ab minor pentatonic, Ab blues, Ab natural minor, Ab dorian and Ab mixolydian.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where Ab7sus4 sits in it. Every scale.
Change one note of Ab7sus4 and you have (drop the flat seventh), (the flat seventh becomes the second), (the fourth becomes the minor third), (the fourth becomes the major third) or (add the ninth).
Ab7sus4 is a suspended chord — root and fifth, with a second or fourth where the third would be — or nothing at all. Suspended and power chords on every root.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.