Maurice - I remain in staunch refusal to have choosen any definition. Although you may use an organ as an instrument, the sounds coming from an organ and the acoustics of the room so placed in vary to such a degree that "magician/arranger" usually more accurately applies.

Just in case you are unfamiliar with the Steve Miller song "The Joker"...
http://www.gangster-of-love.com/songjok.html#5

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artsy-fartsy
rude attitude
lean, mean fighting machine
gender bender
lovey-dovey

Humour goes down easier with bitters.