It’s important to understand, what is the reason for audio phase cancellation and how to avoiding it? One of the most important overlooked perspective of recording is to make sure that all the microphone in phase when more than one is to be used at the same time. The reason is because with only a single out of phase mike and multi mike instrument like a drum kit just never sound right if not corrected would never be able to be fixed.
So, what is phase? Without getting into a technical interpretation, it means that the outputs of all microphones used on the session are pushing and pulling together as one. If one Mike is pushing while another is pulling the cancel each other out at certain frequencies. Well mike number one signal peaks mike number two signal valleys. That frequency cancel each and the result is a very weak sounding signal when mixed together. Here both mikes are pushing and pulling together.
Peaks signal happen at the same time as does their valleys. As a result their signals reinforce one another. Two types of phase cancellation problems is available and it can happen electronic and acoustic. An acoustic facing problem occurs when too much or too close together and pick up the sound from the same instrument only one is picking it up a little later than the first because it’s a little farther away. In Acoustic, the phase won’t cancel each other out completely only at certain frequencies.
When the two were mixed together this usually makes them sound either hollow or just lack depth and bottom end. The way to eliminate the problems by moving Mike number two a little further away from Mike number one if the mikes are directional make sure that each one is pointing directly at the source of the trying to capture.
The 3-1 principle states that in order to avoid phase cancellation between microphones. A second mike should never be within three times the distance at the first Mike is from its source. For instance if a pair of microphones replaced over the sound board of a piano at a distance of one foot separation between the two mike should be at least three feet. If the distance from the source was to feed the distance between the mikes should be at least six feet. This principle is not a hard and fast rule but it certainly is a good guideline for eliminating phase problems. Remember if you record something with phase problem no amount of EQ or processing can ever make it right afterwards.