Phase between multimiced instruments tends to be completely overlooked by home studio producers and engineers. Yet the negative effects of bad phase relationships can ruin the potential of your mixes. Instead of avoiding the problems lurking in your mix, check out this easy 5-minute technique and make light work of fixing phase issues in Logic Pro.
Fix Phase Issues in 5 Minutes
Phase issues can be such a pain.
Get a little too eager and decide to track some drums with 15 different microphones? You, my friend, are going to be double-checking phase on those 15 mics for a while.
How come? Because you're faced with a dilemma. Each microphone is "hearing" your instrument from a different angle and place. But not only that, the time it takes to reach each microphone is different. For example, your overheads and kick mic both pick up the sound of the kick. But it takes more time in milliseconds for the kick sound to hit the overhead mics. Whereas the kick mic captures the sound almost immediately.
Which results in some unfortunate circumstances. Your top snare mic is out of phase with your bottom snare mic. The time discrepancy between your room mic and close mics can make the drums sound empty and phasey. All robbing your mix of weight and substance.
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What is Phase?
Plainly put, phase is the movement of sound. If we were to visualize audio, the waveform would move in a cyclical fashion. Up and down, and up and down. Imagine a wave lapping on the beach. The wave smacks the sand, and then recedes back. Then imagine your ear drum, and how it vibrates in response to sound.
For example, here's a waveform of a snare and how it travels:
Where phase problems often occur is when two microphones are capturing the same sound. In our snare example, the top mic's waveform will be completely opposite of the bottom mic.
As you can see, the two microphones are "hearing" the snare, but from opposite sides. The result is each mic's perspective of the sound is "flipped."
As the top snare mic's waveform goes up, the bottom snare mic's waveform goes down. When you hear these two mics together, the snare will sound hollow and far away. In other words, they're out-of-phase.
Our usual method for fixing phase is with polarity reversal. Which Apple's Logic Pro team was kind enough to give us in the Gain plugin:
When you insert the Gain plugin on your top snare mic and press the Polarity button, Logic Pro "flips" the snare waveform.
So you then go through one mic at a time. Your job is to listen to each drum against the overheads, flipping polarity to see which way sounds better. You might even listen to each drum against the other drum tracks to double-check.
Sometimes "in-phase" can be tough to figure out. If your recorded tracks were in an untuned space like a bedroom or basement, they'll likely have more phase issues.
Time's Impact on Phase
Let's throw some more problems onto the pile. Not only can you have flipped waveforms, but you can have waveforms that are out of time with each other. Take for example this snare and overheads:
Predictably, the snare mic "hears" the snare drum much sooner than the overheads. The difference in time can cause the snare to be out-of-phase with the overheads. What we end up with is a smeared image of the snare. Which can have phase issues as well.
It's worth pointing out though – differences in time between mics doesn't automatically suggest a problem. As always, your ears are the final judge.
The Left-Right Method to Fixing Phase
While tuning your ears to phase is important, you'd much rather get down to EQing and compressing, right? Well, it turns out there's a very easy and fast way to fix phase issues in Logic Pro.
What you'll need:
- A correlation meter
- A gain plugin
Correlation meters are wonderful for figuring out phase issues of stereo mixes and tracks. They're also great with multimic instruments. We'll use our multimic drum scenario as our example:
- Solo and hard-pan your overheads to the left
- Solo and hard-pan your kick drum to the right
- Cycle a kick drum hit and hit play
Go ahead and open your Correlation meter. Which side is the meter reading? If it's the right, or +1 side, your kick is in-phase with your overheads. If the correlation meter is bouncing around on the left side, your kick is out-of-phase with the overheads. If the meter is on the left side, go ahead and flip the polarity on the kick drum. Now your kick is in-phase.
Now hard-pan your kick to the left with your overheads. Solo and hard-pan your snare drum to the right. Now go ahead and repeat the process.
Need to fix some issues with time? You can repeat the process with Logic Pro's Sample Delay on the track that hits first. Voxengo's Sound Delay plugin is free and allows finer control over time.
A free Correlation Meter from MAAT in case folks don't have Logic Pro: