How to Prevent or Fix Phase Issues in the Studio

Say you’ve finished recording all of the instruments and vocals and you want to mix everything down. The individual tracks sound great, but once you start playing with the faders, it sounds like all parts of the recording are working against each other. The mix is all but up to snuff, and a phase issue is most likely to blame. In this blog, I’m going to explain what phase is, what it causes and how you can get rid of it, so you can prevent or fix any phase issues as they pop up while you’re working on your studio projects.

What’s Phase?
Polarity
Time Delay
Reflections
Phase Issues During Mixing
See Also

First Off

I’ll be referring to a number of audio samples throughout the blog. Here they are:

1a. Polarity Issue (snare drum):

1b. Polarity Issue Fixed (snare drum):

2a. Time Alignment Issue (double bass):

2b. Time Alignment Issue Fixed (double bass):

What’s Phase?

As you probably already know, sound is essentially nothing more than changes in air pressure. These fluctuations are usually indicated in wave-form as seen in the images below. Expressed in degrees, phase lets us know where we are within the wave-motion. If you’re recording a sound source using two or more microphones, you’re dealing with multiple waves that are played back at the same time. When the waves are in sync, they’re ‘in phase’, in which case the sound coming out of your speakers will be twice as loud. On the other hand, the waves are ‘out of phase’ when they cancel each other out, so to say. In reality, sending non-synchronised waves to your speaker makes it move its woofer forwards and backwards at the same time, resulting in a strange, thin sound or even complete silence. Phase issues can be caused by a number of factors, so let’s look at some of the most important ones.

Polarity

Snare drums are commonly recorded via two microphones: one up top and the other set up below. If you were to stick both microphones on the opposite sides of a vibrating surface, each would register the exact same sound waves, but they would oppose one another. (see image 1a). Listen to audio sample 1a and you’ll notice that there’s barely any low-end left. If polarity lies at the heart of your phase issues, the solution is simple: just flip the reverse-polarity switch of one of the two tracks to synchronise the waves (see image 1b). Check out audio sample 1b. Sounds much fuller, doesn’t it? If your audio interface, microphone preamp or mixer features individual phase-reverse switches per channel, you can already fix any phase issues while you’re still recording. If not, you can always do so later on using your DAW software.

Image 1a – Polarity Issue:

Fase-problemen: polariteit-probleem

Image 1b – Polarity Issue Fixed:

Fase-problemen: polariteit-oplossing

Time Alignment

Whether it’s a snare, a guitar or a bass, if both microphones aren’t set up at the same distance from whatever you’re recording, you’ll definitely end up with delay issues – even if you’re using a DI. In image 2a, you can see that delay causes the two tracks to be critically out of sync, and in audio sample 2a you can hear what this does to a double bass recorded via a microphone and a DI box. Once again, the solution involves the phase-reverse switch. By simply reversing the polarity of one of the recorded microphone signals, you can immediately bring both tracks back in harmony. If you do this, however, the same delay that caused the phase issue in the first place will still be there (see image 2b). As such, another way to solve the problem is to eliminate the delay: either via your DAW software by zooming all the way in until you can see tiny waves and then dragging the track forwards until it lines up with the other one, or by applying a sample delay to the first recording that enters the mix (see image 2c). Have a listen to audio sample 2b and you’ll notice that the double bass sounds a lot tighter and richer thanks to a few deliberate milliseconds of delay on the DI track. Don’t worry, just a couple of milliseconds of delay doesn’t make it sound like the band can’t keep time, and if you can’t be bothered to align the tracks manually, check out plug-ins like Pi and Auto Align.

Image 2a – Time Alignment Issue:

Fase-problemen: looptijd

Image 2b – Time Alignment Issue Fixed (Polarity):

Fase-problemen: looptijd-oplossing 1 (polariteit)

Image 2c – Time Alignment Issue Fixed (Delay):

Fase-problemen: looptijd-oplossing 2 (delay)

Reflections

Reflections are also known to upset the apple cart. Place a microphone close to a reflecting surface like a wall, and it’ll register both the sound coming directly from the sound source as well as any reflections bouncing off the wall. Since reflections take more time to reach the microphone, they’re delayed compared to any directly-captured sound. As you now know, time-alignment issues can remove chunks of frequencies from recordings, even if you’re only using a single microphone. There’s no getting it out once this so-called comb-filter effect enters your recording, which is why it’s so important to prevent it. Make it a habit to check, test and tweak your set-up, and only start recording once you can’t hear anything that shouldn’t be there. Just so you know, microphones equipped with a cardioid or supercardioid pickup pattern can prove really useful here since they can be positioned in such a way that any unwanted reflections are directed at the microphone’s ‘blind spot’.

Phase Issues During Mixing

You may encounter phase issues during the mix-down, where equalisers and multi-band compressors can easily cause significant phase-shifts in parts of the frequency spectrum. While you won’t immediately notice any shifts if you apply a little equalisation to a snare and listen back to it by itself, listen to the snare along with the overheads and you might just find that your fat snare sound has turned into the sound of snapping twigs. If that’s the case, see if you can solve the issue via a phase-reverse switch, by adding a sample delay, or by using a linear phase EQ. As the name suggests, this type of equaliser doesn’t generate phase shifts.

So, how do you deal with phase issues? Do you know of any ways to make phase work in your favour? Feel free to share your insights in the comments below!