Originally Posted by: john15rhodes

Asus2 is spelt 1 2 5 whereas Aadd9 is spelt 1 3 5 9

Both 2 and 9 are same pitches, only difference is that 9 is an octave higher than 2.

For A chord 2 and 9 is B.

Asus2 has major(or minor) third replaced by second. Aadd9 is a triad chord with added 9th.

A major, 1 3 5, A C# E

Asus2, 1 2 5, A B E

Aadd9, 1 3 5 9, A C# E B

The difference between sus2 and add9 chords is whether the third is present or not.