When it comes to cutting a drums loop or a melody that has been sampled you have two options: do it manually with an audio editor or use a program like ReCycle!, which is capable of generating REX and REX2 files, that can play the samples in which a loop is divided on any sampler software.

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The program has an aspect similar to that of any other audio enhancement program, with the big difference that this tool can only be used to detect volume changes, apply a noise gate and optimize the dynamics of any sound sample that has a rhythmic base (electric guitars, drums, percussion, electric pianos,...).

Once the cutting points have been marked on the loop you'll have the option to export them in REX format (ideal for the virtual instruments included in Reason), export the “pieces” as independent files or generate MIDI files to maintain a sample's groove.