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There is an easier way of automatically mapping rex files to the EXS 24 instead of Ultrabeat.
Here is a fairly tedious method of converting a Recycle Rex file into Ultrabeat in Logic so that you can play the loop mapped to your keyboard like you can with Dr. Rex in Reason:
-Create an audio track
-Drag the rex loop into your audio track from the finder (it creates a folder with each sample slice in it matched to your tempo)
-Open your bin (‘b’)
-Click the down arrow next to the rex loop converted .aif file
-Select all of the parts (0, 1, 2, etc)
-Choose Save Regions As…and save to your audio folder
-Create a new instrument track and load Ultrabeat
-Click on a key in Ultrabeat and click on the sample button in the synthesizer section
-Above the sample button, click on the current sound file and choose Load sample
-Navigate to your audio folder and choose the first file you saved (file 0, etc). Repeat this for each sample you want mapped to the keyboard
You can now save this preset in the top menu with ‘Save Setting As…’.
The alternative is to slave Reason via rewire to logic, but this way you can have it all in one project, which is less processor intensive.