Does it matter if I EQ before or after the compressor?

EQ before the compressor

The compressor's detector measures the level of the signal it is given. If that signal carries low-frequency rumble, or one resonant note that jumps out, the compressor turns everything down each time that energy appears. The result is pumping caused by something that should not be in the signal at all. Remove it first, and the compressor responds to the performance.

Cuts go first for that reason: high-pass filters, notches on resonances, a dip in a boxy range.

EQ after the compressor

A boost placed before a compressor is partly undone by it. The boosted range becomes louder, the compressor reacts to it and turns it back down, and it reacts more to that range than to the rest. Placed after, the boost stays exactly as set. Shelves that add air or weight, and any broad shaping, go here.

The usual chain

Corrective cuts, then compression, then tonal shaping. Each stage gets a cleaner signal than the last.

When to break the rule

Boosting before a compressor on purpose makes it clamp down on that range, which can be useful on an uneven bass or a harsh vocal. The order is a choice about what the compressor should respond to. It matters most when the compressor is working hard: at 1 or 2 dB of gain reduction the two orders sound nearly the same.

In Zammoth

Devices are freely ordered. Drag a device's header sideways in the dock and an insertion line shows where it will land. A chain has one EQ, drawn as one box with all its bands, so by hand you place that box before or after the Compressor. The engineer can go further and place the compressor between two of the EQ's bands. The EQ then runs in two places and its box is marked SPLIT ×2. See the manual on the device dock.