Phase might seem like one of those black magic production or mixing topics, though once you get the hang of phase problems, you’ll understand how to use it or avoid it at any time. Come with us to explain to you this term, how to fix it, and how to avoid that.
Phase cancellation is when two signals that use the same frequency are “out of phase” with one another, which results in an overall level reduction of the combined signal that we call deconstructive interference. When two identical signals are entirely out of phase with one another, meaning they are 180-degrees out of phase, they will cancel each other out.
Come with us to explain to you this term, how to fix it, and how to avoid that.
What does in phase and out of phase means?
‘In phase” and “out of phase” are phrases that we often use to describe the phase relationships between two or more signals. We determine the phase relationship by looking at where the positive and negative peaks sit in relativity to one another.
More often than not, engineers use the term “out of phase” to describe signals that are approximately 180-degrees opposite from one another. The proper term, however, would be “inversed polarity,” where polarity refers to a signal being backward from the other.
Phase implies a delay in time. The more out of phase a signal is with another; the more significant the delay will be.
How Do You Hear Phase problems?
One of the primary ways that people hear phase is comb filtering. Comb filtering is when a sound adds to itself within a short interval of time. That time ranges from around 1ms to 25ms. The result found on a frequency response graph is signals that resemble a comb.
Comb filtering can sound different depending on the original signals that you are using. Comb filtering that occurs under 20 ms will sound scooped, weird, or ‘phasey,’ while comb filtering that happens over 20 ms will typically sound like a delay.
Another thing that you will likely hear is a loss of bass frequencies. Let’s say that you are summing together two kick drum microphones, and you notice that your kick sounds a bit weak when they are both together. The problem is likely not the sound of the kick drum itself, but the phase relationship between the two microphones.
As for phase cancellation, you might not hear the combined signal at all when you sum the two sources together.
How do you check phase issues in a mix?
One of the most popular mixing techniques to check for hard-to-hear phase issues in your mix is by listening to your mix in mono.
If you control your mixing console with a monitor controller, that controller probably has a mono switch. You can press the mono switch to hear you mix fold into the center. If you don’t have an interface or controller with a mono switch, you can use a mono plug-in on your master bus.
Brainworx bx_solo is one of our favorite plug-ins for this use.
One way to use the mono technique is to loop the main section of your track, such as the chorus part or any other part where many instruments are playing. Flip your mix back and forth between stereo and mono using your mono switch as your track plays. You’ll want to listen for any elements that drop out, lose volume, or shift in terms of tone when you hit the mono switch.
There are specialized plug-ins that we can use to diagnose phase issues as well. One of our favorites is the PAZ Analyzer plug-in from Waves. This plug-in utilizes a Position component that shows any phase issues present in your mix.
How do you fix phase issues in a mix?
- Phase Invert Switch
One of the best and easiest ways to deal with phase issues in your mix is flipping the phase invert switch. Most stock EQs come with phase switches, which look a little bit like this.
If you have two tracks in your DAW, which you believe might be out of phase or having phases issues, you can stick a plug-in with a phase switch on it and flip the polarity of the track by 180-degrees by engaging the polarity switch.
Let’s say that you have a phase issue on your drum multi-track. Here is a simple procedure you can go through:
- Solo the kick and the overheads while listening to your mix in mono. If your mix has multiple mics on the kick or snare, check the phase on those first before bussing them together.
- Insert an EQ or any other plug-in with a phase switch on the kick and flip the phase.
- If your kick sounds fuller and more natural, keep the phase switch where it is. On the other hand, if it sounds weird after you flipped it, then flip it back the other way.
- You can repeat this process with the overheads against the snare, the overheads against the toms, etc.
However, one extremely important thing to note is that there are tracks that have phase issues even when they are not 180-degrees out of phase. These types of situations require subtle adjustments rather than a simple polarity flip.
Once you have made any of these adjustments, we recommend committing or printing the track so that you don’t accidentally go back out of phase down the line.
- Manual Phase Adjustment
Another way to fix phase issues in a mix is by manually adjusting your tracks. All DAWs present you with the ability to slide tracks forward or backward on the timeline.
Let’s say that you have two snare drum mics that don’t quite sound right. You can zoom in to the waveforms on your DAW and see if there are any timing discrepancies between the two. Then you can adjust the tracks so that they sit right on top of one another.
As you can see, the acoustic guitar DI in the photo above is slightly in front of the mic track. To remedy this, we would take the mic track and pull it a bit to the left until it lines up nicely with the DI track.
We highly recommend saving a copy of your session before doing this. One of the biggest mistakes that beginner mix engineers make is completely butchering the timing when they begin manually moving around multiple microphones, especially when it comes to drums.
Having the ability to revert to a mixing ‘checkpoint’ is very helpful.
- Pitch Shifting
If you are still struggling with phase issues, you can try pitch shifting one of your signals by a few cents. A pitch shift plug-in, such as SoundShifter Pitch from Waves, can be used to do this. Detune one of your signals by as much as 10 cents. Listen carefully to make sure the detuning doesn’t harm the integrity of the song.
Pitch shifting has the potential to change the timbre of one signal just enough to fix the issue.
- M/S Processing – Side Low Cut
One technique that is extremely useful for dealing with phase issues in a mix is getting rid of low-end on the sides of your mix using M/S processing.
The idea here is that we don’t want to have low-end information (typically below 150-200Hz) clogging up the sides of our mix. When the mix is folded to mono, these low frequencies cause quite a few problems.
Let’s say we have a stereo synth that is fairly wide. We start by using Izotope Imager 2 to see if we have a problem. If the white dot on the interface reads between 0 and -1, we know we have a low-end spread problem.
We can then use FabFilter Pro-Q 3 to fix our stereo image. To do this, we add a low-cut filter and engage it so that it is only working on the sides, as we want to maintain our low-end information in the center. The slope should sit fairly steep around 96dB per octave so that we are completely removing all of the low-end information from the sides.
Once this is done, Ozone Imager 2 should read +1, meaning all of the phase cancellation issues are fixed.
Also, you can easily know if your audio has phase cancellation issues when you will open the stereo analyzer / or stereo imager.
- Reducing the “Width” Parameter
For this example, we used Izotope Imager 2. As you can see in the red section, it’s showing negative values. It’s a sign of phase canceling issues. You can also hear it as there is almost no low-end (bass.) You should always keep the values close to “+1” to keep the integrity of the stereo image, especially in the low-end area.
And here is the fixed version. We easily fixed that by reducing the stereo field. To do that, you can use any of the following plugins like Izotope Imager 2 or Waves S1 Stereo Imager and reduce the “Width” parameter.
Common Phase Problem Areas
If you take the time to record your signals properly, you shouldn’t have to deal with any phase problems. Of course, the world isn’t perfect by any means, and in many cases, we have to work with tracks that are problematic in terms of phase.
Here are a few common areas to check for phase problems:
- Multitrack Drums: The most common source of phase problems comes from multi-track drums. Engineers often record drum kits with multiple microphones at varying distances from each element of the kit. You must always check for phase problems when recording or mixing drums.
- Simultaneous DI: Bass, guitar, or any other instrument that you record using a DI and a microphone must go through a phase check. A sound that travels through a DI arrives before the microphone.
- Stereo Instrument Recordings: Acoustic guitars or other instruments that utilize multiple microphones during the capture process are very susceptible to phase issues. When summed to mono, the timing differences between the two microphones can create problems.
- Faulty Wires: While it is very rare, engineers sometimes experience electrical phase problems. Electrical phase problems occur when a connector within a cable or piece of gear is wired backward. In this case, you could end up with a sound that is 180-degrees out of phase.
How To Avoid Phase Cancellation In Your Mix
One of the best ways to avoid phase cancellation in a mix is by repositioning your microphones during the recording process.
Often, producers or engineers will use multiple microphones to record a single instrument. When you record a snare drum, you might mic the top and the bottom. If you do not properly place those microphones, you might get phase cancellation.
Phase cancellation happens when one microphone is a bit further away than another microphone recording the same signal, meaning the further microphone receives the audio signal at a later time.
If you aren’t able to reposition your microphones, you can use the reverse polarity or phase switch feature in your DAW or on one of your plug-ins, as we mentioned before.
People often use stereo synth sounds in their mixes, which are panned completely to the left or right. It is necessary to pay close attention to how these synths sound when they are in mono. More often than not, stereo synths utilize phase manipulation to achieve width.
If the sound isn’t the same in mono, this isn’t necessarily a bad thing, but it is worth understanding.
If you are making use of MIDI to trigger your stereo synth sounds, you might want to go in and adjust your soft-synth preset to make it more phase-coherent.
Take Caution With Stereo Wideners
Producers often use stereo wideners to achieve wide mixes. Stereo imaging sounds fantastic when in stereo, though you must check how it sounds in mono to see how the process is truly affecting your mix.
Most stereo widener plug-ins use phase manipulation to create wider images. These plug-ins don’t sum to mono very well.
We’re not saying that you shouldn’t use them in your mix. We’re just saying that you should be careful when using stereo imagers.
Beware of Doubling and Hard Panning
People will often take mono sources and use doubling techniques to fake stereo recordings. When tracks aren’t sufficient enough to sound exciting in a mix, doubling is a great way to add excitement. However, you must do this with caution.
One example is when you have a vocal take, and you record the same take on top of it and pan one hard left and one hard right. In stereo, they might sound nice and wide, though when summed to mono, phase issues may start to occur.
One way to fix this is by recording doubles differently. If you are doubling vocals, for example, you might want to change microphones, use a different part of your voice, or stand in a different place while recording.
If you’re double-tracking guitars, which engineers often do in rock-centric genres, it is best to double-track with different guitars and amps to avoid phase issues when you sum the tracks down to mono.
Start Your Mix In Mono
One radical yet brilliant way to mix is completely in mono. When you perform all of your processing, including volume balancing, EQing, compressing, and more, up the middle, you have a much better chance of getting it to sound beautiful, wide, and in-phase once you begin messing with your pan pots.
Mixing in mono forces you to make better EQ decisions as well, which can help you avoid phases issues when your final mix is summed to mono on some devices once it is out in the world.
Why Is Low-End & Sub Region Crucial For Phasing?
Low-end frequencies and sub frequencies are crucial to pay attention to during the mixing process as they are most susceptible to phase issues. For this reason, we recommend keeping your low frequencies in mono.
One problem that beginner producers often struggle with is the desire to use wide synth basses. We don’t blame them. Wide synth basses sound incredible! H0wever, when summed to mono, they are not very phase-coherent.
If you do want to use wide synth bass or any other similar instrument with wide low-end frequencies, follow these steps:
- Duplicate your synth bass track.
- Put a parametric EQ plug-in on both of your tracks.
- Use a low-pass filter on one of your synth bass duplicate tracks and pull it all the way down to 200Hz.
- On the other track, pull a high-pass filter up to 200Hz.
- The track with the low-pass filter should be kept completely in mono to avoid phase issues, while the track that has the high-pass filter can spread across the stereo field, making the bass less-resistant to phase problems.
Tuning Your Kick
Phase cancellation often occurs in electronic music when producers tune their kick drums to the same fundamental as the key that their song is in.
Let’s say that your song is in A minor, and you decide to tune your kick drum to A. Your kick drum will potentially run into issues with you sub-bass, which could result in a warbly, phasey sound.
If you are noticing problems, try to tune your kick drum up or down in thirds or fifths and stick with whatever sounds best.
How do I stop microphone phasing?
If you are using two microphones on a signal and you notice they are out of phase, you might want to try a more phase-coherent microphone set up, such as:
- XY Stereo
- AB Stereo
- Mid-Side Stereo
XY Stereo is one of the simplest and most phase-coherent microphone techniques around. Simply position two cardioid microphones at right angles while keeping the front capsules aligned. Typically, engineers will use small-diaphragm condensers for this type of microphone set up.
This mic set up is wonderful for close-mic applications, especially if you don’t need your stereo image to sit wide.
If you want to mic something from a medium distance without worrying about phase, you might want to consider the AB Stereo technique. The AB technique uses a set of cardioid or omnidirectional microphones that are aligned parallel to one another.
This particular microphone technique is wonderful for tracking groups of vocalists or the room around a drum set.
The mid-side stereo technique is pretty much known for its phase-coherent qualities. All you need to set up the mid-side stereo technique is a cardioid microphone, which will act as the middle or “mid” microphone and a figure-eight microphone that will act as the side microphone.
Arrange your figure-eight microphone so that it is facing the left and right. Next, place your cardioid microphone on top of the figure-eight microphone and direct the face of it towards the sound source.
Once you have recorded both of your signals in your DAW, you duplicate your side microphone and flip the phase. Pan the non-flipped channel to the left and the inverted or flipped channel to the right.
This microphone technique will give you a wide stereo image without any phase issues.
Utilizing the 3:1 Rule
If you are planning on miking a distant sound source with more than one microphone, we recommend using the 3:1 rule, as it can help get rid of interference and phase cancellation.
The 3:1 rule says
For every unit of distance that a microphone is from a sound source, the microphone that is closest to it should be placed at least three times that distance.
If you have a microphone one foot away from your sound source, for example, you should place the next microphone three feet away from the first microphone while keeping your capsules on the same plane.
Sometimes single microphones can experience phase problems as well.
Sound takes roughly a millisecond to travel one foot, meaning we must be cautious about the differences in time between the direct signal hitting a microphone and room reflections of that signal hitting the microphone.
One great example of this comes from when we close-mic electric guitar cabinets with a single microphone. The majority of the sound is picked up from the signal leaving the speaker and hitting the microphone capsule. However, that same microphone capsule will also pick up reflections from the floor underneath it, especially if your flooring utilizes reflective material, such as vinyl, concrete, or wood.
One of the best ways to remedy these time differences is to soak up the reflections with room treatments. You can use rugs, foam, or acoustic panels to tame reflections in the room, which will help minimize microphone phasing. You can also refrain from recording too close to reflective surfaces.
As a rule of thumb, it is usually best to record at least a few feet away from any reflective surfaces in a room, if possible.
Using Phase To Your Advantage
Not all phase problems need to be addressed. In fact, sometimes, the phase can be used to enhance a mix.
Let’s take the example of two microphones placed on a guitar cabinet. Those two microphones could be used to add a unique texture or color to the tone of the instrument. You can manipulate the blend between the two microphones to create a sound that catches the ear.
Many engineers use phase cancellation to create depth. If you multi-mic a drum kit with many microphones that have complex phase relationships, this could end up smearing the transients, leaving you with a nice kit blend that sits back in the mix a bit better.
When it comes to phase, there isn’t one golden rule to follow. Make sure that you are always A/B’ing the decisions that you make