Aadd9 is A, C#, E and B — with the ninth added, and no seventh.
It sounds bright and ringing. No seventh at all: that is what “add” means, and it is why this sounds open where a maj9 sounds lush.
Tonic — a triad with one colour on it.
Also written A(add9), Aadd2 or A add nine.
Going from E to Aadd9, the ninth of the IV is the fifth of the I. Keep that note on top of both chords and it ties them together, which is much of why the pair sounds so good.
Listen for: The top note never moves: the fifth of the I, then the ninth of the IV. On the plain IV it drops a whole step.
Heard in“Overture” from Tommy
In which keys. Every note of Aadd9 belongs to C# minor, D major, E major, F# minor, A major and B minor.
Every note of Aadd9 is in A major pentatonic, A major, A mixolydian, A lydian and A lydian dominant.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where Aadd9 sits in it. Every scale.
Change one note of Aadd9 and you have (drop the ninth), (drop the major third), (the major third becomes the fourth), (the ninth becomes the major seventh), (add the major seventh) or (the major third becomes the minor third).
Aadd9 is a major chord — root, major third, fifth. Major 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.