What is Phase change recording?

What is Phase change recording?
When recording a snare drum with a mic on the top and the bottom, a phenomenon known as phase cancellation can occur. Sound is a wave. A property of waves is that they can interfere with each other destructively and constructively. Imagine the sound waves caused when hitting a snare drum. The waves from the top of the drum will go into the top mic first, then the bottom mic. The waves from the bottom of the drum will go into the bottom mic first then the top mic. Because of the timing of the waves as they arrive at each mic, they will destructively interfere, and many of the frequencies integral to a good snare drum sound will be low in gain (volume). So a good audio engineer will use a phase reversal lead on the bottom mic. This is just like a normal lead, only the positive and negative pins have been reversed, and the phase cancellation will not occur.