Connect a USB cable to the "USB Out" jack on the rear of your MPC 2500. Connect the other end to the USB port on your computer. Typically USB ports are located on the left side of laptops and on either the front or rear of desktop machines.
Connect a MIDI cable to the "MIDI Out" jack on the rear of the MPC 2500. Connect the other end the "MIDI In" jack on the audio interface.
Connect your audio interface to your computer with a USB or Firewire cable. The type of cable required varies according to the make and model of your interface. For example, the Focusrite Saffire Pro interface has a Firewire connection.
Double-click the "Reason 4" icon on your desktop screen, or open the program from the "Start" menu. If using a Mac, double-click the icon or open Reason 4 from the "Applications" folder.
Click "File" and select "New Track." Click "Set up," "Preferences" and select the "MIDI" tab. On the "MIDI" tab, select the MPC 2500 device and click "Default Thru Instrument" to assign to MPC 2500 as the default MIDI controller. Leave the "MIDI tab" open.
Assign samples to each pad on the MPC 2500. Press the "1" button and scroll through the sample menu on the screen. Once you see the sample you want, select "Enter." If you have no samples on your MPC 2500, select them from the Reason 4 library and drag them onto the MPC 2500 icon in the Reason 4 interface. Reason 4 automatically recognizes the MPC 2500 as an external USB drive as well as a MIDI controller.
Hit "Record" on the Reason 4 interface and begin triggering your samples from the MPC 2500. Press one of the 12 pads on the front control unit. If you are using a click track in Reason 4, the MIDI connection automatically synchronizes it with the MPC 2500, which enables you to quantize any out-of-time samples later.