Dual-Mics: Dealing with Phase
Place your Mics on your desired cab. I usually put one off-axis at the Dustcap, and one "on-axis" at dead-center of the cone. This is fine with both Mics on one speaker, or separating them onto two speakers. Make sure the guitar and amp sound fine and that the amp is at a comfortable recording level.
Then, put the guitar down. Unplug it and stick the cable to something that will make noise, even if that is someone holding the end of the cable between 2 fingers. The noise must be stable and constant. Once you have your constant, slightly annoying hum, go to the control room.
Make sure you are setup to monitor the levels for each individual channel, plus you L/R Mix Buss. Turn your Ref. Monitors/Headphones down, as this will get pretty damn loud. Using your console/interface/mic preamp (your input gain/trim), bring Mic 1's noise up to -0db on your DAW/Console's channel meter. Once you've got the signal to zero, mute the channel. Then, repeat the step for Mic 2.
Now, very importantly, pull Mic 2's FADER (NOT the input gain) down to -infinity. Unmute Mic 1. Slowly push Mic 2's fader up towards zero.
If the volume on your final L/R Mix Buss goes up, you need to flip the phase of Mic 2. If you don't have phase switching, make an out of phase cable. To do this, take an XLR cable and reverse the connections for pins 2 and 3. Don't forget to label that particular cable, so you know what it's for and don't end up trying to track OH's with it or something. Flip the phase until the volume on your Mix Buss goes down, with both Mics at -0db. Now your Mics are out of phase. Good. Next...
You'll need everyone in the studio to either get out, or be completely still and quiet. No fucking around NOW. Go out to the amp with headphones on. You will hear a hissing/humming/amp noise... make sure the amp noise in the cans is loud enough not to hear the actual hum from the amp. VERY IMPORTANT: DO NOT Speak, Cough, Sneeze, Burp, Vomit, or even Fart. You'll be next to the mics, so the high volume in the cans could seriously rupture your eardrum.
Now, extremely carefully(and without disturbing Mic 1), move Mic 2 back and forth, left and right, slowly. You should hear the phase swishing in and out, just like a phaser or flanger pedal. The trick is to find the spot where the least amount noise is coming out of the headphones. Keep moving the mic until you find it.
You are looking for the spot where the two mics are the most in phase with each other. If one is phase flipped, then at the most "in-phase" placement, they will nearly cancel each other out. Once you find it, take the cans off, plug the guitar back in, and go back to your control room.
Turn both mic preamp/input gains all the way down. Mic 1: Set the channel fader at the -0db position on your console/DAW. Have the guitarist play while you turn up the mic pre/input gain until you hit zero, then mute Mic 1. Repeat the step for Mic 2, bring it to -0db.
Unflip the phase on Mic 2, and your Dual-Mics are in phase.
Unmute Mic 1 and start messing with the faders for both. Go up and down on them both in any number of combinations until the overall sound makes you happy. Once you get a sound you like, buss them together and send em to a track, or keep them separate for more Mix control later on.
**If I left anything out, just let me know, and I'll fix it.
-Tommy
