Amadd9 is A, C, E and B — 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.
Minor tonic — a triad with one colour on it.
Also written Am(add9), Amin(add9) or A-add9.
A folk-rock phrase in a minor mode can come home through C and G to Amadd9. The ♭VII’s third is the ninth of the i, so it holds over and colours the landing.
Listen for: A half step down to the ♭VII’s third, which then holds as the ninth. On the plain minor chord it falls a whole step to the root.
Heard in“John Barleycorn”
In which keys. Every note of Amadd9 belongs to C major, E minor, G major and A minor.
Every note of Amadd9 is in A natural minor, A dorian, A harmonic minor and A melodic minor.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where Amadd9 sits in it. Every scale.
Change one note of Amadd9 and you have (drop the ninth), (drop the minor third), (the minor third becomes the fourth), (the ninth becomes the sixth), (add the sixth) or (the ninth becomes the flat seventh).
Amadd9 is a minor chord — root, minor third, fifth. Minor 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.