Launch your digital audio workstation and create a MIDI instrument or sampler. If you are using Reason as your workstation of choice, create an NN-XT sampler device by clicking on the "Create" menu at the top of the screen and selecting this device. If you are using Logic, create an EXS24 sampler by adding a new software instrument track and selecting the EXS24 from the menu that appears on the right.
Load the audio you wish to control with a MIDI device into the sampler by assigning the audio track to an individual button or key on your MIDI controller. Within the NN-XT, this can be accomplished by selecting any pre-assigned .WAV file present on the keyboard map and clicking the file folder icon in the "Load Sample" box in the top left corner of the device. Click the "Edit" button within the EXS24 to bring up a complete listing of assigned .WAV files and their location on your MIDI controller. Click the small down arrow next to the .WAV file you wish to replace and select "Load Audio Sample" from the menu that appears.
After you have selected the file you wish to use, the audio you have imported will be assigned to the key or button on your MIDI controller that you have selected. MIDI assignment can be made by selecting the individual key or button you would like to use within the menus of the NN-XT or EXS24.
Test your MIDI controller by pressing the key assigned to the audio file you have previously selected. If you followed the previously listed steps correctly, your desired audio should play immediately after you press the key. You can assign customized audio samples to each key on your MIDI controller. After you have made all of your desired assignments, the audio you have imported will be able to be controlled using MIDI data input.