This article was originally published in Guitar Interactive magazine issue 55
Scratch the surface of recording and you’ll run into some discussion about phase; make sure the microphones are in phase, flip the phase of one of the guitars, phase align the mic and the DI, and so many more. It’s actually all quite simple once we understand a couple of basics, and sort-out one very common misunderstanding. OK, here goes….
What is phase?
Imagine a simple sine wave. Imagine a second identical wave that goes up and down at the same time. Those waves are “in phase”. Add them together and we get a wave that’s the same shape but bigger – Fig 1.
Polarity is that very common misunderstanding . Imagine the two waves that we started with back in Fig 1 going up and down at the same time. This time, we’re not nudging anything, we’re just going to turn one of them upside down. The effect is pretty much identical to the “180 degree out of phase” we saw in Fig 2, and, again, if we add them together, they will add up to zero. There are no in-between polarities – it’s the same or it’s opposite.
Polarity is what people mean when they say “flip the phase”, it’s what the “phase” button on a console or DAW does, it’s what happens when we get the wires in a mic cable connected the wrong way round, it’s what happens when we mic a snare or a cab from both sides, and it’s also what happens when we wire our guitar pickups “out of phase”. Polarity is nothing to do with time, it’s simply making one of the waves upside down.
…. and this matters why?
So far, we’ve considered waves where every up/down cycle is identical. Add two identical waves that are 180 degrees out of phase and they behave pretty much exactly the same as if we reversed the polarity of one of them. But – we really don’t tend to record simple repeating wave patterns. Real recorded wave forms look more like Fig 4
….and in real life? In the next Making Tracks we’ll take a look at what we need to watch-out for and we can do to fix phase problems.