Anderton
bitflipper
General rule #2: effects that alter amplitude precede effects that react to amplitude. Example: HPF (reduces lows) precedes compression (responds primarily to lows).
The main exception to that general rule is that compression after EQ will "undo" some of the effects of EQ. For example if EQ reduces low frequencies, compression will bring them back up a bit. So if the emphasis is on a change caused by EQ, then you'd want to follow the compressor.
But putting EQ before compression also has another use. With a dance mix where you want the kick to really pump, if you EQ after the compressor and boost the kick frequencies you'll likely overload anything that follows. If you push going into the compressor, the kick will sound louder but not take such a toll on the headroom.
Does compression always undo the effects of EQ if applied after? I would imagine that the fact that compression alters amplitude over time whereas EQ alters amplitude in a more static manner would have a big effect on which frequencies get affected and how. For instance, let's say we have a compressor that is post-EQ (the EQ is removing some low end) acting as an envelope shaper. A kick tends to 'pitch down' over time. Knowing that, if you have the compressor set to compress the latter 'half' of the sound, leaving the transient alone, aren't you effectively lowering some of that low frequency content while the higher frequency click remains relatively untouched? This is assuming we haven't touched the make-up gain. And of course, this is only one example and I would love to know what you think.