Operator`s manual

Appendix
Page 222
the external sequencer, then set both the Soft thru and Local mode
fields to OFF. These fields are in the screen accessed by pressing the
MIDI key and selecting option 2.
When I play a key on my keyboard synthesizer while connected to
the MPC60, two voices play in my keyboard for every one key
pressed. Why?
When you play a key on the synthesizer keyboard, it plays the note
internally and also sends a note over MIDI to the MPC60. Because the
MPC60’s Soft thru feature is normally set to ON, that note is immediately
sent back out to the keyboard, causing it to play the same note again. To
solve this problem, turn Soft thru off (press the MIDI key, then select
option 2) or disable Local Control on your keyboard synthesizer.