Phase Interference: Don't Phase Me, Bro
Remember the days of playing on giant trampolines, perfecting the back flip and flirting with the edge? Remember when it seemed like a good idea for jumper #2 to come aboard? Remember how every bound became unpredictable, with some leaps uncannily propelled, and others snuffed out like a candle, reduced to a measly foot-high awkward air spasm? Well, those embarrassing spasms don’t happen to stop at the tramp’s edge, as they are infamous for corrupting far beyond childhood birthday parties.
The point here is that speaker cones basically function like trampolines, and similar issues can arise as sounds are propelled off of a diaphragm. If the two kids jumping are perceived as projected waveforms, then their interaction of energy is essentially the unwanted phenomenon of phase interference.
While tracking, phase interference (or cancellation) typically occurs in the overhead, room, and top/bottom snare mikes. Simply moving the microphones until it sounds good is the first step to avoiding interference. And for the overheads, it’s best to position them equidistant from the snare. Additionally, some engineers prefer to use placement strategies like the 3:1 ratio. However, this method is somewhat flawed. Because phase relies strictly on frequency and its coinciding wavelength, when a single drum produces a hodgepodge of harmonics, some frequencies from the drum will be in phase and others will be out at any two given points in space. An additional method of phase herding is to simply flip the phase switch on a preamp.
During mixing, phase becomes an issue when adding effects in certain DAWs, most notably Pro Tools LE, as any plug-in could potentially add a slight delay to a signal and push it out of phase from other tracks. Thankfully, many DAWs, like Pro Tools HD, Cubase, and Ableton, offer the easy remedy of automatic delay compensation.
In the monitoring stage, speaker and head placement are paramount. Sitting at the sweet spot has the most aligned phase patterns. To screen for interference, be sure to monitor with speakers rather than headphones (also try setting them to mono) as the physical cancellation cannot occur within the confines of headphones and the brain does not detect phase discrepancies.
Listening is the best defense. Monitor everything. For stereo tracks, isolate left and right channels. Solo each individually and then audition them together. Their combined effort should be louder. Louder is better. It makes you want to jump up and down.