In tertian music theory, the chords are basically pancaked every other note. These sound nice and harmonious due to the ratio of the frequencies.

     In the G Major chord pancake we have G xa B xc D for G-B-D, chord scale numbers 1, 3 and 5. Extending these sonorities continues in the same pattern, next is the 7 chord:

1-3-5-7  |  G-B-D-F

     Only the highest number is displayed starting on 7, going through 13. These are the extended chords.

     Finally, we get to the beautiful 9 chord, G9:

1-3-5-7-9  |  G-B-D-F-A

     "add2" is signaling to voice the chord as GABDF. This moves the A down one octave nestled in between G and B. Essentially, the 123 cluster is the desired effect.

     "sus2" is signaling that the chord begins with an A that will resolve to G or B. 2 can go to either 1 or 3 in this case since they are equally distant apart at a whole step. G to A and A to B.

     Resolving to 1 sounds more complete and resolving to 3 is more suspensful.

Take the G9 Chord Music Test

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What are the notes of G9 chord?

Take the C9 Chord Music Test

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What are the notes of C9 chord?