|Separation and phasing|
Placement of microphones in different positions relative to the drumset and to eaxh other brings a couple of implications that shoukd be considered
The next choice is what you want each microphone to pickup. If you want to keep the high hat out of the snare mic (as much as possible, anyway), a cardioid or hyper-cardioid is a better choice than an omni. But for overheads and room mics an omni may be just the ticket. There really aren't any rules, so grab as many mics as you can and experiment.
Life would be easy if you could just get every drum sounding good on their own, and then they just sound great together. Life is rarely that easy, thanks to phase relationships.
As an example, let's look at the following scenario:
The snare is miked with an SM57. Sounds great. The rack tom is miked with an MD421. Sounds great. But when both channels are up, it sounds weird. That's because the snare mic is also picking up a little bit of the tom, and vice versa. This is called mic bleed. If the tom bleeding into the snare mic is out of phase with the tom in the tom mic, the tom can sound thin when struck. Without delving into physics, it's important to stress that moving either mic in this situation by as little as a 1/4 of an inch can fix the phase problem. So listen to all the mics together and make little changes until everything sounds good together.
Tip: A good thing to remember is that the volume of a source is halved when you double the distance. So a mic 2" from a drum will pick up that sound twice as loud as a mic 4" away. So even though two tom mics might only be a foot apart, if they are 1-2" away from the tom they're trying to pick up, you still will have a reasonable amount of isolation. If you're careful and what bleed remains is in phase, this is not a problem.
At this point, you're probably thinking, "I'll just gate it." While gating is a subjective subject, I do recommend that you not track with gates. Wait until mixdown for that. That way you can experiment and get it right, rather than live with a hasty decision while tracking.