Why is the mid-range EQ so important? This is where your ear is picking up most of the frequencies. Your ear picks up frequencies from 20 Hertz to 20K, if you didn't know that already. Really, most of the main information that's happening is between 5K down to about 200. That's where a lot the stuff is going on. That's where things get really tight and congested. A lot of instruments play around that area. That's why the mids are super important to get right.
I actually think that the low-mids are the most important place to get right. That's where it gives you the most energy, the most feel and the most width, and things like that. The top end of the mids is more from 2K upwards, and that can start getting quite hard. That's really piercing. Your ear really picks up a lot of frequencies around 1K, 1.7K, things like that.
When you start adding around 1K upwards, it's really going to start piercing your ear, and you're going to be able to put less on at 1K than you would at about 400 because your ear picks it up more. But really, what you want to do is try and leave the mids, and leave the high end of the mids and the tops and just get the low-mids really weighty and tight. I always suggest maybe adding a bit there and just seeing if that actually pushes it out.
What you've got to watch out for in the low-mids is things can start getting a bit boxy, because as I say, there's a lot going on. It's quite a lot of information. Try not to get it boxy sounding, just try half a dB here and there – a good little tip just to get things sounding nice and fat and big, and without sounding too harsh and in-your-face by worrying too much about the high mids.