Optimally, the point of EQ in mixing is not to make each track sound better. This is something to do at the source, in the recording process. The point of EQ is to carve out a spot in the spectrum for each instrument, so their frequencies don’t overlap and produce a muddy or cluttered sound. This creates a feeling often called ‘air,’ ’space,’ or separation in the mix.

All instrument recordings have dominant frequencies - places in the spectrum that define that instrument’s sound. A bass guitar, for example, has its dominant frequencies below about 500hz. If you set a low pass filter at 500hz on a bass, you might not notice the difference in sound, because most of its defining characteristics are in that range. You’ll notice the same effect if you set a high pass filter at 1khz on some cymbals, because their dominant frequencies are not in the low end.

(Note that this is a basic approach to mixing with EQ. Pass Filters and Shelving EQ are great tools for learning, but they shouldn’t be used frivolously. For example, using an LPF at 500hz on a bass would kill the attack and leave you with a fairly lifeless sound.)

Unfortunately, things aren’t that easy. Songs obviously don’t consist of just bass and cymbals. The bass’s dominant frequencies overlap with toms and the kick drum, guitars overlap with vocals, and synths and keyboards can go all over the spectrum. Otherwise, we wouldn’t really need parametric EQ (or mixing engineers). Your job is to figure out what can be cut from a signal, and what can’t. (I’ll go into depth on this next time.) Don’t forget there are other tools as well - panning and reverb can help with separation just as much as EQ.