It’s Just A Phase
Unfortunately, there are hidden dangers when layering kicks. The first is phase cancellation. This is when sections of the waveforms in your kick samples are out of phase with each other, effectively cancelling each other out and potentially making certain frequencies of your samples becoming quieter, giving a ‘thin’ sound when the two kicks are layered together. In fact, it’s quite possible to combine two fat kicks and arrive at something lacking low end!
A good place to start checking for phase cancellation is your DAW’s polarity inversion button, often (erroneously!) labelled as phase inversion. Here’s where to find it in Cubase (click images to enlarge):
If your DAW’s mixer doesn’t have this feature, then there are many plugins that allow you to do something similar. Try the Gain utility in Logic or Sonalksis’s excellent FreeG plugin.
Leaving your original kick unchanged, listen to what happens when reversing the polarity of the second kick sample.
Here’s how our layered kicks sound with ‘normal’ layering, leaving the polarity of both channels untouched:
And then how they sound with the polarity of the second kick drum inverted:
Deciding whether the kicks work best with the polarity of one sample inverted is a simple case of trial and error: invert the polarity and if it sounds better stick with it.
It doesn’t particularly matter whether you invert the polarity of the first or second kick; the effect is virtually identical. Similarly, bear in mind that inverting both has virtually the same effect as inverting neither!
Note that polarity isn’t quite the same as phase (although the terms are often used interchangeably). We’ll come back to the deeper significance of that point in the future, but for now it’s important because changing the relative timing of the two samples will also affect their phase relationship, regardless of how you set the polarity inversion buttons.
The best approach is to fine-tune the timing of the two samples first, making sure you’re happy with the way their transients line up with each other (i.e. that the combined result sounds like a single hit rather than two hits slightly out of time with each other), then check for phase cancellation using the polarity inversion button.