RX2 (REX2 Loop) is a proprietary audio file format developed by Swedish music software company Propellerhead for use with their ReCycle music loop editor.

The idea behind ReCycle was to enable music producers to easily create new and/or edit existing music loops, allowing them to alter the tempo of the loops, without changing their pitch and without negatively affecting the sound quality.

Originally released in 1994, ReCycle made a true revolution in computer music production, being the first application to bring the idea of loop slicing to the mainstream. The REX2 file format is nowadays a standard in audio sample looping and is supported by all major DAWs, such as Reaper, Logic, Cubase, Reason and Pro Tools.

REX2 files can either be mono or stereo, and utilize a proprietary non-lossy compression algorithm, which can reduce their file size by up to 60%.

The name REX stands for ReCycle Export, since REX was the native export format for Propellerhead ReCycle.