In studio engineering and recording, phase cancellation can seem almost magical. Many people choose to ignore phase cancellation in order to not learn about it, how it happens, and what to do to fix it. Do not be one of them.
It will be broken down in plain language. I will show you how to listen, what plugins to use if it isn’t obvious, and how to fix any wave cancellation problems. This results in a sharper stereo image that includes all frequencies you desire, but with no spikes in those you don’t.
It is easy to understand and fix these problems. This will give you an edge in any competition and will help your music sound better. These are two concepts that you should know before we begin:
Frequencies Sound waves are cyclic a certain amount of times per second. This is known as Hertz (Hz). A frequency can be defined as the number of cycles, for example 750Hz. This would mean that there are 750 cycles per second. Each frequency has a unique wavelength. Therefore, phase issues can occur at certain frequencies but not at others.
Phase: The sound wave cycles start at a particular time. If two identical cycles start at the same moment, they are called “in phase”. One cycle can be delayed so that the waveforms are inverted (at 180 degrees), it is “out of phase.” You’ll usually be between 0 and 180 degrees. For a visual aid, see below.
What is Phase Cancellation?
Deconstructive interference is when audio waves from different forms collide with one another. This is called phase cancellation. This results in a decrease of volume at the frequencies where the problem is. You can also experience the opposite effect, which causes an increase in amplitude.
This can occur at different intensities depending on how out of phase two recordings are and how similar their amplitudes or wave forms may be. This is difficult to comprehend when you combine physics with music industry jargon. I will keep it simple.
If two waves collide and the peak frequencies of one frequency coincide, the resulting amplified frequency for that frequency can be up to twice as loud. The troughs can also be affected by waves. A peak and a valley (the highest and lowest points of a wave) can meet and cancel each other.
What is Phase Cancelling?
Wave forms are complex, with many timbres and frequencies coming from different instruments. You’d expect this to be rare. It’s usually only two times that you have to listen carefully for it. The third is easy to solve.
Recordings of the same audio source are the most common culprit. For example, two microphones can be used to record stereo of an acoustic instrument. Poor microphone placement is the main culprit. This is achieved when you duplicate a track and then pan them to create stereo width. Room acoustics is the third.
POOR MIKING TECHNIQUE IN STEREO RECORDING
Bad miking techniques can cause frequency cancellation. Bad miking technique can cause the sound waves from an instrument to reach different microphones at different times. This increases the likelihood of a complete silencing or severe disruption in the audio quality.
This can still occur if you have the exact same microphones picking up the same sounds at the same distance. It could lead to two tracks that are perfectly synchronized. This can cause volume increases, while perfectly out-of phase recordings can be muted. You can also have everything in between.
Stereo recording requires that the tracks are perfectly aligned. Frequency increases are acceptable since they are meant to be identical tracks. You can hear cancellation occurring when the tracks are out of phase.
DOUBLING INSTRUMENTS AND HARD PAANNING
Wave cancellation can also be caused by taking a mono recording (one-channel) and multiplying it to create a fake stereo recording. This is used to mix tracks that are not sufficient to create an interesting mix.
One example is having the backing vocal track of one song doubled and then panned in opposing directions. This technique is often used by many people, but they don’t know that it’s the Haas Method. It’s based on the Haas Effect we’ve discussed here.
The wave forms of the doubled track are identical so you won’t hear panning without delay. Phase issues can develop if you panning too much.
Mixing engineers often fail to notice it when using headphones or near-field monitors. This is because the waveforms never intersect in the air before reaching the ears. The problem is obvious when the music is played back later in a car or on a home stereo.
COMB FILTERING STARTING FROM ROOM ACOUSTICS
Comb filtering is a harsh-sounding problem. Comb filtering is caused by sounds that reflect off the walls in your studio and arrive at the microphone in phase.
The wave form is characterized visually by steep notches that look similar to the teeth on a comb. This creates the large teeth that are its nameake, the big teeth.
How to Prevent Phase Cancellation At The Source
All three causes of audio phase problems are easy to fix. These issues can be avoided by making sure that your mix is clean from the beginning. We’ll then discuss how to fix them when it’s too late.
X-Y TECHNIQUE AND THE 3:3 RULE WITH SPACE PAIRS
Let’s start with microphone placement during recording. You can use either one of the two miking methods when recording a single source. The X-Y technique employs two microphones that are as close as possible to each other, but aimed precisely 90 degrees apart.
The sound waves arrive at the same time, but because the microphones are pointed in different directions, you will get slightly different recordings. For example, bass frequencies on guitar and piano will be to the left, while high frequencies will be to the right. These differences allow your ears to experience stereo sound, without cancellation.
Sometimes, you might not use the XY technique because you need a larger stereo image or if you are recording a large group like a bluegrass band or choir. Spaced Pairs is a method that uses two or more microphones spaced apart.
The 3:3 rule states that each microphone should be three times farther apart than the one next to it. The physics behind these distances will not be discussed, but they are very useful in combatting phase problems.
DEFEAT COMB FILTERING – ACOUSTIC TREATMENT
If your microphones are picking up comb filtering (which is the opposite of phase cancelling), this means that they are accurately recording the reflections of the walls in phase. First, move your microphone a little further away from the wall. This will stop the sound, but it will not make your results better.
Acoustic treatment is a type paneling that is mounted on walls and absorbs sound waves, converting them into heat. This prevents them from bouncing back at you microphone.
Also, you’ll get clearer and more pristine recordings. This is the best investment you could make. It should be followed by a good preamplifier. Although it’s not exciting or fun for most people, it really makes a huge difference even with low-quality recording equipment.
Identifying Phase Problems
You’ve either recorded a performance using multiple microphones to create a stereo track, or you’ve doubled the pan of an instrument to create stereo width. You can’t hear the phase issues, so you don’t know if they are there. These issues may still exist, but they are less severe. Here are some ways to spot it.
You will be stuck with the problem if you bounce or combine two recordings. You can keep the tracks separated, but output them all to one auxiliary bus. You can then solo those tracks, and then switch from stereo to mono.
You can read our mixing mono article for more information. The quick summary is that most gain plugins include a mono button, or you can search for a directional mixer plugin to allow you to do this. You’ll be able to hear any phase issues by forcing the tracks to merge into one channel.
If you are unable to hear the track, switch from mono to stereo and use a phase correlation plugin. This plugin will detect and tell you if the tracks are “in phase” or not, since they are combined into one mono signal.
+1 means that you are in phase and -1 means that you are out of phase. 0 is the widest possible stereo image without any phase issues. Phase correlation plugins work only on stereo tracks. However, they will work fine on an auxiliary bus if you’re not still summing to Mono.
How to Fix Phase Audio in the Mix
While you don’t have to worry about getting slapped up against +1 every time, you should keep your head above 75%. Phase cancellation occurs when the meter moves to the left by more than 75%. Let’s get it fixed.
1) DELAY A PANED SIDE
First, choose the right or left paned track and then add a delay. You can use as little as 3 ms to 5ms, or up to 15ms. True stereo recordings will have a noticeable delay. However, it is acceptable for doubled tracks.
2) DETUNE WITH A PITC SHIFT
If that doesn’t fix it, but it still has problems, pick a side and tune it by a few dollars. This can be done with a pitch shifting plugin. As long as the sound isn’t too bad, you can increase the detuning up to 10 cents. This will alter the timbre to resolve the rest of your problem.
3) POLARITY FLIP WITH PHASE INVEERT
If you still have problems, you could try the nuclear option. This is where one track’s phase is inverted. Combining the two previous methods can resolve the problem completely. You can even back off a little. However, it may not always work and could lead to the opposite problem of filtering combs. It’s best to save it for the end.
Phase Cancellation Be Gone!
That’s it. We were able to understand the problem better through a long explanation. However, the solution is quite simple: Phase Invert , Delay, Detune . Any other explanation would be absurd!
It’s not so bad, you see. You can learn phase cancellation from many studio engineers, which is something you can do better than them. Your current clients will be more than happy to learn about phase cancellation and your music will sound better. Have fun, and have fun mixing!