REX Files are files created in the ReCycle program. This is an application created by Propellerhead Software, used for slicing up music loops and enabling them to be played back in any tempo. In Reason, REX files are primarily used in the Dr. Rex loop player, but they can be used in the NN-19 as well. Possible extensions are ".rx2", ".rcy" and ".rex".
When loading a REX file, each slice in the file is assigned to one key, chromatically. All parameters are set to default settings.
When using REX files in the DR. Rex loop player, it is possible to make a track play the slices in order to recreate the original loop. To do the same in the NN-19 requires a few extra steps.
1. Use the patch browser to load the REX file into an NN-19 sampler.
2. Create a Dr. Rex loop player and load the same REX file in to this device.
3. Use the To Track feature on the Dr. Rex to create playback data (a group) on the track assigned to the Dr. Rex.
4. Move that group to the track that plays the NN-19 and play it back from there.