I know you’ve felt this before. Thin mixes.
It’s easy to identify, but not quite as easy to fix. Unless you know where to look.
If you’ve got a thin mix, chances are you’re missing some crucial frequencies. Those are usually going to be around 150 Hz to 400 Hz.
The first thing you’ll want to do is work with the arrangement. This is the best way to fix a thin (or muddy) mix.
So you’ll want to either add some new tracks (like rhythm guitars or a lower piano), or you’ll want to look at the EQ you’ve got on those tracks.
If that doesn’t solve your problem, then you might want to look at the level of your bass guitar. This is usually the culprit for thin mixes. If your bass is just too low in the mix, you’ll be missing out on a lot of those thick frequencies.
Final thing to try is to cut some of the high mid and high frequencies in your mix. The tracks that usually cause problems up there are the overheads, high guitar parts, and even some synth parts. Tame those back with EQ and your overall spectral balance should be better, giving you a more even mix that doesn’t sound “thin.”
Try these out and you should be able to beef up your thin tracks pretty quickly!