A friend of mine sent me the tracks for his album, and he has already done some mixing work, so there are some quiter parts and some louder parts. He wants the difference in loudness between those parts to be even more pronounced, so that the quiter parts get even quiter in comparison to the louder parts. Apart from manual automation, is there a quick fix for this?
I'm working with Reaper, so I was pondering if there might be some kind of script that could be like "decrease the levels of all parts that are below X db by 3 db" or something of that kind. Moreover, I was also generally thinking about easy loudness automation tools.

 

thats a gate/expander, there are many options you could pick from.
if you have the ozone suite i think there's one module inside. The Pro-G from ff is another option.
Idk Reaper but there's probably something in stock too.

 

An example with kilohearts Dynamics (free), which does both in one plugin:



Below the 45° line: Make stuff quieter than it is.
Above the 45° line: Make stuff louder than it is.

You can also smoosh the two threshold levels together if you want a transition point rather than a transition band.

(IMO you should just write automation though)

 

This script you're talking about is called Envelope Based Compressor

 

Expanders do exactly that but I'd suggest as others to just do a manual automation