I've had experienced players tell me that add9 2nd... it doesn't matter... that it's the same scale degree

but to me octave difference matters

and it's just occured to me that with say a Dsus2[br]The 2 REPLACES the 3 and I guess that's just because it would sound muddy, and on guitar probably impossible to play both?

[br]but with a Dadd9 the full triad is there with the ADDITION of the 2nd an octave higher (9)

so yeah... is that the technical difference

9 is an octave higher in addition to the 3

whereas sus2 replaces the 3

why's it called sustained?