I wrote my own effect for processing stereo guitar tracks to automate pan moves based on stereo width of the incoming signals.
It's a little hard to explain in a one-liner, but basically it monitors the stereo width of the incoming stereo guitar sound (e.g. direct from a stereo effects unit or an Axe-Fx or similar) and adjusts the panning of the inputs from a configurable starting position to a configurable ending position for each channel when the width crosses a certain threshold. A simple attack/sustain/release envelope controls how the panning is interpolated between the starting and ending positions. The open and close thresholds as well as attack/release times are configurable as sliders.
I use it for my band's rehearsals. We rehearse via headphones with all inputs mixed in software. Both our guitars are direct in and make no noise in the room. Same with bass. The only things making noise in the room are the drum kit and the singer so it makes it easy to mix in software and pump through headphones.
The way I use this effect is to move a guitar part from either the left or right channel into a stereo sound half-way towards the center depending on the incoming stereo depth. The incoming stereo depth change is just a trigger for when a guitar lead is played with lots of stereo effects enabled, e.g. a ping-pong stereo delay, or stereo flangers or choruses. The guitar widens out so you hear the width when it is introduced and then collapses back into mono and pans back to where it started when the lead part is over.
https://github.com/JamesDunne/Reaper...o-pan-width.js
File is also attached to this post.
Thanks!