The Hammond Clone contained in the GarageBand App for iPad is quite cool. The only drawback is that Apple does not provide a MIDI implementation chart.
Because I wanted to know which codes have to be sent to control the Leslie simulator and the chorus vibrato I hooked my iPad2 up to Logic and virtually tried every single Control to find out which ones worked and which ones didn’t.
To make it short, the iPad GarageBand does not respond to most of them, but I found a few useful ones:
Volume: CTRL 7, 0 – 127
Pan: CTRL 10, 0 – 127
Expression: CTRL 11, 0 – 127
Leslie slow: CTRL 64, 0
Leslie fast: CTRL 64, 127
Chorus Vibrato off: CTRL 65, 0
Chorus Vibrato on: CTRL 65, 127
Important Note: The controls on the screen do not change when the control messages are sent to the iPad. So there is no visual control of the settings!
Also have a look at the revised sound comparison chart which now contains the iPad organ