Phase Cancellation: The Drum Sound Destroyer

July 30, 2012, by Bobby Owsinski

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This article is excerpted from Bobby Owsinki’s “The Drum Recording Handbook.”

One of the most important and overlooked aspects of drum mic’ing is making sure that the mics are all in-phase.

This is really important because with only one out-of-phase mic, the whole kit will never sound right, and if not corrected before all the drums are mixed together, it can never be fixed.

So just what is phase anyway? Without getting into a heavy explanation, it just means that all the microphones are pushing and pulling together.

If one mic is pushing while another is pulling, they cancel each other out. Check out the diagram of Figure 1.

In this figure, both mics are pushing and pulling together. Their signal peaks happen at the same time as does their valleys.

As a result, their signals reinforce one another. In Figure 2, when mic 1’s signal peaks, mic 2’s signal valleys. They cancel each other out and result in a very weak sounding signal when mixed together.

Acoustic Phase Cancellation
There are two types of phasing problems that can happen—electronic and acoustic.

An acoustic phasing problem occurs when two mics are too close together and pick up the same signal at the same time, only one is picking it up a little later than the first because it’s a little farther away.

Figure 1: Two microphones in-phase.

With acoustic phase problems, the sounds won’t cancel each other out completely, only at certain frequencies. This usually makes the mix of the two together sound either hollow or just lacking depth and bottom end.

The way to eliminate the problem is by moving mic 2 a little further away from mic 1, or if the mics are directional, make sure that each one is pointing directly at the source that they’re trying to capture.

Keeping the mics parallel to each other, or at a 90-degree angle for mics underneath drums will also really make a difference.

Electronic Phase Cancellation
Why would there be an electronic phase problem? Almost all of the time it’s because a mic cable is mis-wired; it was either repaired incorrectly or originally wired incorrectly from the factory (which is rare).

There are two ways to check the electronic phase.

Checking Phase The Easy Way
Here’s a very easy way to check mic phase, although not as precisely as method #2 shown later.

After you get a mix balance of the kit together, flip the phase selector on each mic channel one at a time either on your console or on the DAW.

Whichever position has the most low end, leave it there. Do this on every mic in the kit (select the overhead and room mics in a pair, but check the left mic against the right as well).

Checking Phase The Slightly More Difficult Way
This method takes a bit more work, but you’ll know for sure if you have a mic cable that’s wired backward. Also, you really have to have another person with you to make this work. It’s a two-man operation.

First you have to pick a mic and make it your “reference.” Any mic on the kit will do, but it’s easier to pick an overhead or a mic that can easily come off the stand.

Figure 2 Two microphones out-of-phase.

Now take your reference mic and put it next to another mic on the kit, say the kick drum mic, as in Figure 3. Make sure that each mic is at the exact same volume level in the speakers, not fader level.

Now have someone talk into the mic while you switch the phase selector on either the console or DAW. Again, choose the selection that sounds the fullest.

Do this to each microphone. Any channel that has its phase selector different from all the others has a mis-wired cable. Make sure you mark it so you don’t have the same problem again!

Times When You Might Want The Phase Reversed
There are times when you should definitely consider flipping the phase before you start mixing.

Figure 3 Checking the electronic phase.

As we said before, there may be some acoustic phase issues as well because even though a mic may be further away than another, it may still be picking up the same source.

In the following cases, the phase should be flipped to overcome an acoustic phase problem.

An Under-Snare Mic: The under-snare mic should just about always be flipped out of-phase.

Any Under-Drum Mic: Anytime a mic is placed underneath a drum, it’s phase should almost always be flipped
out of phase.

Room Mics: Depending upon where they’re placed, how much room reflection they’re receiving, and how high they’re used in the mix, sometimes the room mics sound a lot better if the phase is reversed.

Overhead Mics in Extremely Rare Cases: Once again, it depends upon how high they’re placed above the kit, what kind of reflections they’re receiving and if they’re the main sound of the kit, but on rare occasions it might sound better (meaning fuller) if the phase is flipped.


 
Editor Note: This article is the first in a series on drums, excerpted from Bobby Owsinki’s “The Drum Recording Handbook”. Other articles in the series are available here.

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