There are two ways to work in front of an EQ. One is moving things until it sounds better, which works sometimes and teaches nothing. The other is hearing the problem, knowing which zone it's in, and going straight there. The difference isn't talent: it's having a map of the spectrum internalised enough that «where is that?» has an answer before you touch anything.
Frequency Drop trains that map by association rather than memorisation: it hands you an instrument and you drop it into its band. There are 7 zones — SUB-BASS (20–60 Hz), BASS (60–250 Hz), LOW-MID (250–500 Hz), MID (500 Hz–2 kHz), HIGH-MID (2–6 kHz), HIGH (6–12 kHz), AIR (12–20 kHz) — and 15 instruments, from kick to shaker, and the point is that after a few rounds you stop thinking in numbers and start thinking in places.
Almost no instrument lives in a single place, and the game reflects that: every card has one perfect zone and several acceptable ones. A snare has its body low and its crack in MID (500 Hz–2 kHz); a piano has the widest range of any instrument here, which is why it accepts four different zones. Hitting the perfect zone scores more, but a reasonable answer doesn't sink you — because in a real mix it wouldn't either.
All three levels are free and play without an account, in the browser. Rounds run 90 to 110 seconds, meant for one before you sit down to mix.
Because instruments occupy ranges, not points. An electric bass has its fundamental in BASS but its definition in LOW-MID, and both answers describe something true. Scoring only one would teach a false map.
It's useful if you still have to sweep to find things when you open one. Knowing what a filter does and knowing where to look are different skills; this is the second, and it's the one that saves time every session.
EQ Surgeon: there it's no longer about which zone an instrument lives in, but about hearing the specific curve someone applied to it.
The full map, band by band with each zone playable, is in the frequency ranges guide. What to do with what you find is in the EQ guide, and the week-by-week plan for the whole ear is in train your ear. Once it's clear, the next exercise is hunting the exact frequency by ear in EQ Surgeon.