What are phasing issues? That’s when the sound waves picked up by a microphone overlap with sound waves captured by another microphone, canceling some of the frequencies from one or more of these soundwaves. Or, put more simply, “it's when your sound noodles overlap and then it cancels out some of the sound noodle”.
When audio phasing issues occur, the consequences can lead to poor sound clarity and depth, or certain frequencies nullified, resulting in an unnatural and hollow sound.
Drum recording is especially prone to phasing issues. When recording drums we tend to use a lot of microphones, while cymbals resonate at high frequencies. It can get messy very quickly. One way of avoiding phasing issues is by applying the 3:1 rule.