EQ or Compress first?
As always, use your ears. But think of the three C's as a rule of thumb, "Cut, Compress, Character." What I mean by this is EQ out problem frequencies, then apply your compression. Then apply EQ to give that "character," or "tone" you are looking for in the sound. If choosing to EQ or compress before has been a daunting task, hopefully this will help! :)
When cutting you'll most likely be using a narrow band width (Q) to notch out the problem areas. If you're not sure where your problem area lies, you can do a sweep. Set a narrow band width and rather than cut, you boost. Start at 20Hz and "sweep" up to 20khz. Resonant peaks... When the problem area get worse or louder, then that's where you need to cut. Additionally, the problem area may not be a part of the sound itself per se, but you might be trying to fix some "Frequency Masking."
*Quick Note - Frequency masking is when 2 or more sounds occupy the same frequency area, and when mixed together they wont sound as good. They may sound fine on there own. An often referenced topic of frequency masking is kick drums and Bass, since they both occupy the low end of the frequency spectrum. They "muddy it up."
If fixing frequency masking, the other element you are mixing will help you determine the frequency area you want to cut with the EQ. Whether you EQ or compress first, you should understand frequency masking.
Compressing will make quiet problem frequencies sound louder, so we cut those first. Compression will make the quiet parts of a sound, louder, and the loud parts quieter. Obviously it's situation specific, for instance if you just want to clean up a sound you should EQ out problem areas before you compress.
After removing your problem areas with EQ, and Compressing, you can EQ to get the "Character" you want. What I mean by character could also be considered tonal-shaping or color. This is where you will most likely be boosting EQs or or making subtle wide band (Q) cuts.
So the answer to whether to EQ or Compress first is to EQ, Compress, and EQ again.
EQ or Compress first summary
- EQ out problem areas within the sound or due to frequency masking.
- Compress - to taste, generally I would say using lower ratios.
- Apply EQ for character/tone/color, often boosting here, or subtle wide band cuts.
Remember the "Three C's," when choosing whether to EQ or compress first.