so i think i know how to sidechain as i tried with just 2 tracks and i get the result i need

but i try to sidechain in a bigger project and for some reason the sound is distorted very weirdly when i try to sidechain......any idea whats causing it?

 

If it's doing something weird like that, then I'd guess it's probably something to do with your routing. Big project, or little project shouldn't matter, unless suddenly you hit the wall for where your interface can no longer handle processing without pops/stutter/distortion (in which case increasing latency in your ASIO driver may help temporarily.. but I'd guess that's not really your issue).

Help people understand a bit better though and preferably provide some screen shots showing how everything is all routed/set up, or explain those connections here. Also, which compressor are you using.

 

The user in front of the daw *SCNR*

Working with Reaper since v3.x (and released a bunch of songs => huge projects) and that never happened. So, it has nothing to do with Reaper, it's something else. As the post before mine said, probably cpu overload and/or too low (asio) latency.