A9 keeps the dominant notes of and includes the : A, C#, E, G and B. A plain 9 chord includes the flat 7th.
The major 3rd and flat 7th still identify the dominant. The 9th can carry the upper line into the next chord.
Also written Adom9 or A dominant 9.
A9 in 3rd inversion puts G in the bass instead of A, the 7th of the chord. The notes are the same; what changes is what the bass line does, which is most of why you would reach for it — it lets the lowest voice move by step where the root would have jumped.
One of A9’s 13 shapes does this:xx5657
A9 goes wherever a dominant seventh goes; the ninth is only an added colour. When the chord resolves, the ninth does what the seventh does and falls a step.
Listen for: The ninth falls a whole step to the fifth of the I. On the plain seventh chord that string plays the root, which just holds.
In which keys. Every note of A9 belongs to D major and B minor.
Contains A9 and adds eleventh and thirteenth.
Adds sharp eleventh and thirteenth, for a dominant sharp-eleventh color.
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.