Reaper's monitor effects chain lives outside of the project, sitting between the output of Reaper's mixer and your audio interface - similar to Cubase's control room. Slick EQ sits at the end of that chain.
The Quiet Mixing Strategy
The most significant issue beginning mixers face is creeping volume syndrome, where everything keeps getting louder.
A comfortable mixing level can be too loud when sustained over long days. When this happens, you lose the ability to judge the decisions you're making.
The simple answer for this is to turn your monitors down. But this presents two more difficulties:
Dan often finds he's been too heavy-handed with reverb and delay when working at low volumes as you can't hear these as clearly at lower levels.
The second is to do with our hearing and how it changes at different volume levels— the equal loudness contours. Our hearing is flattest in frequency responses at relatively loud levels, that'd you would need to raise your voice to talk over. When we turn it down, we hear relatively less of the bass and high treble frequencies - and more of the upper mid-range.
In practice, this means when you check loud, you may have to overcorrect for over boomy kick drums, splashy cymbals and vocals that lack presence.
The equal loudness mode (EL Curve) for the middle band corrects for the reduction of frequencies when listening at lower volumes. This allows you to make the correct mixing decisions by hearing all of the frequencies evenly and having a clear perspective of the mix.
Turning the gain down on the plugin can flatten out the frequency response when you're listening quietly.
Remember to bypass the EQ needs to before bouncing, or when listening loud.