Hi Bob,

In my case, when the music calls for a C7-9 chord, I interpret this as a C7th chord with the 9th note in the C Scale flatted.

When arranging the song I would use the C7th designation in the base "APC" track, and if I wanted to I would use the D flat note in the right hand chord if it fit the melody and if it acomplished the sound effect that I was trying to get.

To me the use of the C7-9 chord is no where close to the use of the Gdim chord as it normally appears in the progression of harmonic chords in the melody of a song.

Having said that, it is always possible to alter the usual chord progression of a song, in order to embellish the listening characteristics of the song to meet the performer or audience's desires.

Just about anything goes if it sounds good.

Just one man's opinion.

Larry Gosmeyer