Phase
From WikiRecording
With regard to electronic signals, phase is defined as a position in time along the waveform cycle. One complete cycle of the waveform is equal to 360° of phase.
 One cycle of a waveform, equal to 360° of phase. |
 Two waveforms, approx. 90° out of phase (also called phase quadrature). |
 Two waveforms, 180° out of phase (also called phase opposition). |
Phase Cancellation
When recording a single sound source with multiple microphones, the sound waves will naturally arrive at the separate microphones at different times. If the sound waves are significantly out of phase, this can cause phase cancellation problems. Phase cancellation can make a signal sound thin and weak.
Solving Phase Cancellation Problems
Think about the 3 to 1 Rule. When using multiple microphones, make sure far microphones are at least 3 times the distance from the sound source than the close mic. This is a general rule that doesn't always apply, but if you look for where you haven't followed it, it can be an easy place to start to root out phase problems.
Move one of the microphones. If one of the microphones is out of phase, simply moving the microphone a little closer or further away from the source can solve the phase problem. also if you have two microphones pointing at the same source from equal distance and opposite sides they will pick up the wave 180 degrees out of phase. (say the bottom and top of a snare drum)
Use the phase switch. Many preamps and mixers include phase switches to flip the incoming waveform 180° but this is only somewhat effective if the signals are not completely out of phase.
Adjust the phase in the DAW. Some DAW software will allow you to adjust the phase of the waveform in the computer. However if you are resorting to this it usually means you didn't record it properly to begin with, this should be only used as a last resort.
