Mastering equalization is made out to be this big, mysterious thing. Something that’s being done in a laboratory-like room by the mastering engineer, dressed in pure white, like a fukken doctor. It’s really not that bad, and it certainly shouldn’t cause you headaches. It does require a certain mindset though, which is a bit different from the one you are used to in mixing. Let’s see what mastering EQ is for, and what it isn’t.
Not a second mixing process
So let’s get this straight right away: you are not supposed to use equalizers for major correction purposes during mastering. If you find the music needs major adjustments, deep, narrow cuts or serious character boosts, go back to the multitrack or send it back to the mixing engineer. One of the main purposes of mastering EQ is to realize the perfect flow between the album tracks, when they’re put in the chosen order. The other major role is to maintain the desired frequency response when the final loudness is created; whether it’s brickwall limiting or converter clipping that’s made the music louder.
You probably know by now how compression can screw with frequencies, even when they can be set to react only to certain ranges of the audio.
Splitting hairs, going for the perfect feel
Anything else you attempt to do with these mastering style equalizers should fall on the subtle side of things. You’ll notice that most of these purpose-built EQs have different, shallower controls compared to their mixing oriented siblings. It’s not rare to only have a couple dB adjustment range, +/-. You’ll usually find low- and high-pass filters, shelves and sometimes wide band bell filters. With these, you can really only tinker with the overall feel or mood of the track, instead of going surgical. And these shallow, subtle filters sound way more transparent, in a musical way. If you need warmth, you can really dial it in with a low shelf, and for the sparkle, just bring in the high shelf until there’s enough of that expensive sounding treble you need.
When EQ is not enough
There aren’t many cases when you need to use anything but subtle EQ moves in the mastering process. But if you really want to go dynamic, or add something that’s not even there, it’s time to go for exciters and saturation/distortion. As distortion adds harmonics to the sound, high frequency content will be created on top of what’s there. It comes handy when turning up the treble with EQ would result in too much hiss. Even in the digital era, it can still happen. Another use of these harmonics is to enhance the low end and make it audible on systems that are not even able to reproduce the lowest frequencies. Mastering has a lot to do with taste, feel and details. But if your mix sucks to begin with, go back and make it sound right, or let us mix it to you.