You need to hook up a midi box and soundcard to your computer. Hook up midi cables, make your computer the master and the MPC the slave, or vice versa whatever is easiest. Press record on a stereo audio channel in ableton, press play on whatever is the master. Set ableton on loop mode.
If you don't know what I mean then read the manuals.
The Associate.
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MPC 2000XL, Dave Smith Evolver, Juno 106, Mackie 1202 VLZ.