If I play the chord: GBDA, then this is considered a Gadd9. But
if I play the 3rd above the 5th (GDB), it is not called a 10th.
Why don't we refer to all notes by 1-7, and is there a system to
picking higher numbers (11) vs lower ones (4)? The distinction
is between interval distances (2nd -> ∞) and chord tones (root,
3rd, 5th, 7th, 9th, 11th, 13th). When you play Gadd9, you are
adding the chord tone that is a 9th above the root. If we just
played a G9 chord, the dominant 7th would actually be implied
(G-B-D-F-A). Playing the interval of a 10th above the root (like
G-D-B) doesn't change the chord. All that does is displace the
chord tone (in this case, the 3rd) up one octave, so it's still
called a G major triad. So, a note would be described as a
fourth if we were talking about interval distances, and an 11th
if it was a chord tone (typically preceded by the root, 3rd,
5th, 7th, and 9th). The exceptions are sus chords and 6 chords.
A sus chord would typically have a 2nd or 4th above the root
suspended in the