QUICK TIP: Phase button first, EQ second
You import the drum tracks into your DAW, then balance the kit, only to notice that the kick drum sounds too thin.
STOP IT RIGHT THERE
Before reaching for the EQ to bump up the lows, use the stock gain plugin (Logic Pro X), or the stock EQ or Compressor (Pro Tools), or maybe it's right there on the channel strip (Reaper)
and click that button that looks like a zero (0) wielding a katana. I mean this one below:
I won't go into the science of phase and polarity, but consider these two scenarios:
1. Your kick drum was recorded using 2 mics on it - inside and outside the drum; close and far, both outside; etc
2. Your kick drum was recorded using 1 mic on it, and it's in the overhead microphones as well.
Fixing the phase issues
The steps to fix the second scenario from above (or at least ameliorate it, see the link at the end of the article) are as follows:
- Solo the kick and overhead(s) channels
- If you have multiple overhead channels, pan them to the center
- Adjust the volume on the tracks so that they're close to being the same. THIS IS VITAL, otherwise you might not hear any difference
- Insert a trim/eq/whatever plugin, one that allows you to flip the phase
- Flip the phase in and out and listen to the difference.
You're listening for a thicker, deeper low end, or for more punch, more attack.
It's easier to hear differences in the low end, than the top end. With experience, you'll be able to hear phasey top end as well.
Flip the phase on every drum track against the overheads, for example, and HEAR what sounds best. If you can't hear a difference, maybe you need to try nudging the regions a bit.
Another situation when you'll want to...
... check the phase is after re-amping bass guitar.
You listen to just the DI track, and it sounds full. Then you listen to the re-amped track, and it sounds amazing. Then you listen to both, and they sound thin and flimsy.
Usually, the time it takes the signal to travel from your interface into the amp, to the microphone and back; this introduces phasing issues.
Flipping the phase on one of those two tracks will greatly increase the instrument's low end presence.
Checking the phase before doing any EQ moves solves many issues you might encounter.
Audiomere's Polarity Maximizer does this for you for all the mics on an instrument at once. At only $49, it's cheap and it saves you quite a bit of time at the beginning of any session. I highly recommend it.
Obviously, getting it right at the source is better than any plugin.
Further reading on phase and polarity
If you'd like to learn more about the science of phase and polarity, common situations when you need to flip the phase, and so on, check out this article on Sound on Sound.