It’s important to train your ears to listen to the different frequency groups. All frequency groups have different characteristics, so they need different treatments. Humans can hear from 20Hz to 20kHz.

• Sub: 20-70Hz: The sub is not musical, and it is only for the body in your track. Sub differs a lot between genres. The soundwaves of sub are large and slow, so there are no transients (fast-hitting sounds) here. There is only a low “whoosh” sound. Sub takes up a lot of space in the mix, so having too much will cause trouble for the rest of the elements. Only the lowest parts of the bass and/or kick is here. Not the rest of the sounds.
• Low mid: 70-200Hz: This sounds musical, and contains the body of a lot of elements. The main part of the kick is here, and the lower, fundamental part of most sounds. Too much of this will sound muddy, too little of this will sound thin. If you want to increase the kick for example, you would boost here, and not in the sub.
• Mid: 200Hz-2kHz: Majority of the music is playing here. The high part of the kick is important here, and the fundamental part of the snare plays here. Higher parts of sounds play here too, and a large part of vocals. Too much will sound boxy, too little will sound thin.
• High: 2kHz-10kHz: Crisp of a lot of sounds, and clarity in a vocal. Second part of the snare is here, and most percussion. Too much of this will sound harsh, too little will sound dull.
• Treble: 10kHz-20kHz: Very high end of the elements. Just like sub, this is not musical. You can’t hear specific sounds here, except for high percussion and maybe the highest part of a vocal. It is mostly for overall brightness and clarity in the song. Too much of this takes up unnecessary space, too little of this will sound filtered. If you want to add brightness to a synth for example, you probably need to boost the high frequencies, not necessarily the treble.

What you should learn from this is that frequency groups may sound different than you expected, and that parts of sounds may be in a different frequency group than you thought. Also, by listening to these frequencies, you can train your ears to hear certain frequencies in full mixes too, so eventually it will be easier to pinpoint frequencies that need changing.

Finally, the exact number of frequencies that make up low, mid, and high can differ across DAWs, producers, and engineers. For example, some people may say that 100Hz is already in the mid, not the low mid. There are no clear-cut rules for this, so you can take the frequency groups a bit more broadly. This is something to remember in general: The numbers say nothing about how something will sound. Always use your ears for that.

As an exercise, open up a song in your DAW, and put an EQ with a low cut and a high cut filter (a band pass filter) on the master channel. For each frequency group, place the band pass filter in a way that only that frequency group can pass through. Listen to your song through these different frequency groups. Also do it with different songs so you learn how each song has divided those frequency groups.