Korg iM1 Owner's Manual page 46

For details on the other effect parameters, refer to the
original M1 owner's manual PDF which is available on
the Web.
Refer to M1 owner's manual PDF, page 36 "3 - Effect
parameters"
Using MIDI CC messages to control the speed of the
Rotary Speaker
When the Rotary Speaker has been selected as an Insert
effect, the rotation speed can be switched using MIDI CC
(Control Change) messages.
Transmitting a CC#76 (Vibrato Rate) message from your
external MIDI device on the MIDI Channel (Refer to "MIDI
Ch" on page 24) with a value of 64-127 will switch the rotary
speed to Fast; transmitting a value of 00-63 will switch the
rotary speed to Slow.
Available Parameters by Mode
46