Akai MPC 4000 Reference Manual page 246

The track assigned to that pad will be muted. Press the pad once again to defeat muting.
Hint: You can use the PAD BANK [A]–[F] keys to switch the tracks that are shown in the display.
You can also switch muting on/off for multiple tracks simultaneously.
5. If you want to solo a specific track, hold down the [F6] key (SOLO) and press
the pad that corresponds to that track.
All other tracks will be muted. To defeat the solo setting, press the [F6] key (SOLO) once
again.
Hint: If you hold down the [SHIFT] key when you press the [F6] key (SOLO) to defeat solo, only the
selected track will be unmuted, and the remaining tracks will stay muted.
6. If you want to record mute on/off operations in the sequence, go to the Track
Mute page, hold down the [REC] key and press the [PLAY] key, and then
perform the desired pad operations.
Your pad operations will be recorded in the sequence as track mute events.
You can overdub by using the [OVER DUB] key instead of the [REC] key.
(For the editing procedure, refer to the following section.)
Hint: Track Mute events are recorded in memory that is independent from conventional track memory.
Tracks in which events are already recorded will not be affected.
Other events cannot be recorded while you are recording mute operations.
The track mute events you record can be edited later.
Track Mute page
237