Here's a walkthrough on how to set up Purr-LUFS in Reaper. To make the setup easier, I’ve also created a script that automatically prepares a track for Purr-LUFS.
What the Script Does:
Sets the track to 4 channels (required for proper routing, since Purr-LUFS needs it).
Handles plugins with more than 2 inputs/outputs since Purr-LUFS only supports stereo plugins and currently can’t compensate for loudness on side-chained plugins.
Automatically bypasses extra inputs/outputs on any plugin that uses more than two channels.
Should be run after all plugins have been loaded to ensure that any multi-channel plugins are handled correctly. Running it beforehand won’t break anything, but it’s only necessary after loading your plugins.
Future Plans:
I'm considering modifying the script to automatically load Purr-LUFS and Purr-Router, but I haven’t decided how to handle different versions. It’s probably best if the user sets that manually.
The script is included in this post—let me know if you find it useful or have any suggestions!