Akai MPC 4000 Reference Manual page 46

Main mode
C Dura% field
Specifies the amount of relative change in duration for each track. Changing this value
will not affect the events recorded in the track.
The Edit Duration popup window will appear if you press the [WINDOW] key.
D Velo% field
Specifies the amount of relative change in velocity for each track. Changing this value
will not affect the events recorded in the track.
The Edit Velocity popup window will appear if you press the [WINDOW] key.
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