What is linear phase EQ? How to use it in your mix
Learn about linear phase EQ and how to correct unintended filtering and phase cancellation on drums, guitars, pianos, and stereo masters.
You've probably used an EQ to shape the sound of a track before, whether in a technical way or for a creative purpose. What you might not have realized is that you could be introducing a new problem in your mix called phase distortion. Let's unpack what that is, what it means for your mix, and how to avoid it by using linear phase EQ.
Understanding phase distortion
Whenever we add a plugin to a track, the computer has to do some quick math to complete the processing we are asking of the plugin. When we add a lot of plugins to a track, this can quickly throw tracks out of sync with each other if some sort of delay compensation isn't employed. Understanding this concept is the first step to understanding linear phase EQ.
When we add an EQ to a track, the bands of frequencies we are adjusting require more processing time than frequencies that aren't being processed. When time is delayed for some frequencies and not others, the phase of the track is changed. This is especially true when using a ton of gain on a band of frequencies or narrow Q values.
What is linear phase EQ?
Linear phase EQs are tools that help avoid the phase distortion that happens when using minimum phase EQ by delaying all frequencies equally so the delay no longer only happens on the particular band of frequencies you're adjusting.
Should I always use linear phase EQ?
The short answer is no. The phase distortion that occurs with a minimum phase EQ is pretty hard to hear. Most often, we hear it when a sound happens across multiple tracks such as on a snare drum when there are mics placed above and below the snare like in the audio example below. This is because there's a phase relationship that already exists between these two tracks so when phase starts to change on one of the tracks, the difference in that phase relationship becomes more apparent. But, it's not always bad. Sometimes the phase distortion sounds good! With Ozone 11 EQ, you can adjust the amount of linear phase EQ applied to the track, rather than having to choose between 100% minimum phase EQ or 100% linear phase EQ.
What is the difference between linear phase EQ and minimum phase EQ?
The main difference between linear phase EQ and minimum phase EQ is that linear phase EQ adds delay to all frequencies of a track, whereas a normal EQ only delays the bands of frequencies that are being processed. Linear phase EQ exists to correct the phase changes that happen with normal phase EQs. Here is an image of an EQ on a snare top track with a linear phase response compared to a minimum phase response. The second image shows the areas where phase shift is occurring and certain frequencies are being delayed. The more drastic the EQ, the more phase shift occurs.
Ozone 11 EQ with linear phase.
Ozone 11 EQ with minimum phase shows the areas where phase shift occurs.
How to use linear phase EQ
Basically, you use linear phase EQs just like you would use a regular EQ. There are controls for frequency, gain, and Q. The main difference is that with plugins like Ozone 11 EQ, you can blend between purely linear phase and purely minimum phase responses to find a happy medium for your music.
We often choose an EQ for the color it adds to a sound. Some of that color comes from the phase relationship between other tracks and with harmonics. When that relationship is changed with an EQ, the result could be anything from a new color of the sound to a less-desired filtering effect.
On tracks full of transients
One of the most common uses for linear phase EQ is on drum kits. With drum kits, you often have a room full of microphones recording the kit. The more microphones there are, the more important it is that they have a good phase relationship.
Adding EQs to each drum track, with each EQ set to process different frequencies, creates different amounts of phase distortion. With so many tracks, these phase changes can add up quickly and blur the transients, resulting in a dull drum sound.
For other tips on EQing drums, check out How to EQ drums.
On stereo sources
Linear phase EQ is ideal for stereo sources such as piano mics, guitar mics, room mics, even on stereo masters. Some mastering engineers swear by linear phase EQs because any phase issues that might not have been bothersome in the mixing stage become more apparent in the mastering stage. Using a linear phase EQ prevents changes in the phase that may exacerbate phase issues.
Start using linear phase EQ to your advantage
Mixing is always about how all of your tracks are working together. When it comes to EQ we often think about how tracks are competing with each other for sonic space and the tone of each instrument, but less often do we consider how adding processing affects the phase relationships between tracks. Listening for how your EQs are affecting frequencies other than the ones you're boosting or cutting is a great listening exercise. For more EQ tips and tricks, visit How to Mix Music and How to EQ Bass.
