Recording Drums Part 5 - Phase Cancellation

Welcome back. Today we're going to look at one of the most important factors in bringing a drum kit recording together. In any recording where multiple microphones are used to capture a single sound source, the phase relationship between each microphone is critical. In particular we need to pay close attention to the relationship between the close mics and room mics.
 

What Is Phase Cancellation?

Without getting too technical, phase cancellation occurs when the signal from 2 microphones picking up the same sound source are out-of-sync with each other. In other words, while one wave is pushing, the other is pulling; if they're 180 degrees out-of-sync, they will cancel each other out at that particular frequency. The result is a very weak sounding signal when combined.

Phase problems regularly happen when recording drums, because typically you're using more than one microphone to pick up each part of the drum kit. For example, if you have a close mic on the snare and a pair of overhead mics, then the sound will reach the overheads later than it reaches your close mic. If the waveforms cancel each other out to any degree, then the recording will lack definition and punch – particularly in the bottom-end.
 

Avoiding & Minimizing Phase Problems

The issue of phase cancellation can be minimized during the recording process by using proper mic technique and the 3-to-1 rule as a guide.
 

The 3-to-1 rule dictates that a second microphone should be at least three times further away from the first mic than the first mic is from its source. For example, if you place two mics on a single instrument and the distance from the source is around 1 foot, then the second mic should be 3 feet away from the first mic. This principle is not a hard-and-fast rule, but it does help as a guide and starting point for eliminating phase problems.

Try as we might, and even when following the 3-to-1 rule, some amount of phase cancellation is inevitable. Therefore, it's important to pay close attention to the relationships between each channel and mitigate accordingly. 

We hope you continue to find this series useful in your pursuit of a great drum sound. Join us for part 6, the final part in our series looking at finalizing the mix. Until then, if you missed the earlier parts of the series, you can start here at part 1, covering setting up and mic technique for drums.