If you are an aspiring audio engineer (either as a hobby or by trade), it’s good to know some of the lingo. One of the things we’ll talk about is phase cancellation.
You’ll learn about what it is and how it pertains to sound. As an audio engineer, it’s nice to understand a bit of the science behind how it all works.
What does the sound do when phase cancellation is involved? What does it actually sound like when you’re listening to a recording?
Believe it or not, phase cancellation is a bad thing. Plus, it’s often one of the more overlooked elements in audio engineering.
Once you have finished reading this, you’ll have a good understanding of what phase cancellation is and how to keep it out of all your audio work.
Let’s dive right in and talk about what it is:
What is Phase Cancellation?
Phase cancellation is defined as two or more sound waves out of phase. The sound waves are supposed to be within the phase of each other.
Phase cancellation occurs when one sound wave hits a peak while the other hits a trough. The sound will be weak when this happens since the frequencies have canceled each other out.
An example of phase cancellation is when you use multiple microphones while playing one musical instrument. Phase cancellation can occur if the mics are not in the proper position.
This is because one of the mics will be farther away from the instrument than one of the other mics.
How to Prevent Phase Cancellation?
One solution is to reposition the mics so they are not far away from the instrument itself. Make sure they are not spaced far apart, but not too close at it may distort the sound.
Ensure that the microphones are a few feet away from the walls and floors. This will prevent any phrase reflected sound from bleeding into the recording.
What Goes on With the Sound Waves During Phase Cancellation?
Sound waves operate in cycles based on their frequency; this is known as ‘hertz’ (Hz).
For example, if the sound is measured at 500 Hz, the sound waves are operating at 500 cycles per second. When two sound waves of the same frequency are in phase, there is an increase in amplitude.
If the sound waves are out of phases, that’s because they are traveling at rates of speed that are opposite from each other. At this point, this is where phase cancellation happens.
Phase cancellation will likely occur during tracking or mixing. That’s why it is crucial to locate the source of the issue and correct it.
For example, going back to the multiple microphones, they need to be as close together as possible to ensure that the sound waves are in phase.
It helps if you abide by the 3:1 rule. To best explain this, for every unit, a microphone is from an instrument (or a source of sound); the next microphone should be three times the distance away from the other.
In other words, that microphone should be at least three feet from the other.
Let’s say you have a choir concert coming up and want to practice using microphones. If you use multiple microphones, the first one should be three feet away from them. Assuming you are using three, the adjacent microphones must be nine feet apart from the initial first microphone.
It’s essential to make sure the capsules are aligned to ensure that the sound stays the same rather than be canceled out. If the microphones are less than nine feet apart from each other, you are breaking the 3:1 rule.
Quick Tips For Fixing Phase Problems
If you are an audio engineer, you want to fix phase problems as quickly as possible. Here are some of the tips we want to share with you on how you can spot them and fix them fast:
Listen For Any Comb Filtering.
Comb filtering is where sound adds a delayed signal to itself. This occurs for a short period.
This usually occurs due to reflections or multiple microphones picking up the same signal while they are positioned in different spots. If the signals are within 10 dB of each other, comb filtering will likely occur.
Comb filtering earns its name because the sound frequencies look like the teeth of a comb when picked up. Sound reflections will be due to sound bouncing off hard surfaces, including floors, windows, and walls.
To avoid comb filtering, you want to identify the reflection source and remove it in any way possible. You can redirect the reflections as well.
You can place the microphone close to the reflection source to prevent delay from both the direct and reflective sounds. As always, you can fall back on the 3:1 rule to help avoid any comb filtering from occurring if you are using multiple microphones.
Listen to Your Recording in Mono.
After listening to the recording in stereo, switch your mixing console to mono. Almost all mixing consoles should have a switch that allows you to shift from stereo to mono (and vice versa).
Be sure to switch back and forth between the two modes and listen for anything that may have dropped out during the switch.
Conclusion
Now that you understand what phase cancellation is, you can be on the lookout for it the next time you are recording sounds. Remember that the sound waves must work in phase rather than out of phase.
Make the necessary adjustments when needed if things don’t sound right. Not every recording has to be perfect on the first take.
As an audio engineer, you’ll want to keep your ears open for any sound irregularities whenever you listen to music recordings. You’ll know exactly what to do to make suitable adjustments when you do.