In the world of audio mixing gurus, you may hear someone praise linear phase EQ as being far superior to “regular” EQ. Let’s set the record straight and identify what is linear phase EQ, how it’s different than regular EQ, and if and why you should use it.
What is Linear Phase EQ
Linear phase EQ is a specific type of EQ or feature available with some EQs.
My favorite EQ and plugin in general, FabFilter’s Pro-Q 3 (see my FabFilter Pro-Q 3 review) has a linear phase EQ feature you can turn on.
At the bottom of the interface there’s the aptly named Zero Latency which I’ll mention in a moment, natural phase, and linear phase:
Essentially, linear phase EQ doesn’t add phase issues which are normally associated with typical EQs.
As a rule, EQ changes the phase of your audio by virtue of how it works.
When you quickly change frequencies, like in the case of especially steep and narrow cuts or boosts, latency is added which changes the phase, resulting in potential phase issues.
Linear phase EQ fixes these phase issues so your sound is unchanged.
How Does Linear Phase EQ Work
Linear phase EQ fixes or removes phase issues by introducing latency to the mix to maintain the proper phasing.
If you’ve ever tried to mix with any kind of latency, you know how frustrating and difficult this makes the process.
With that in mind, FabFilter’s Pro-Q 3 actually has a number of different “degrees” of linear phase you can use.
The most extreme setting of “Maximum” completely removes phase issues but at the expense of a severe delay.
For reference, in a relatively slow tempo song at 72 BPM, it took a full half a bar for the sound to kick in when Maximum linear phase was engaged.
Although not nearly as much of an issue, linear phase EQ is also typically more demanding on your CPU.
It can also add a kind of pre-ringing effect which will be more noticeable on some instruments and can actually take away from your mix’s transients.
Should You Use Linear Phase EQ
While the idea of linear phase sounds superior, at least the phase correction aspect, in practice it’s rarely necessary.
By the way, here is an EXCELLENT video explaining linear phase EQ via FabFilter’s Pro-Q 3 in a couple of very specific examples with Dan Worrall:
He does a nice job showing the potentially positive effects of linear phase when working with two microphones capturing the same audio, particularly when using high or low pass filters. Incidentally and as an aside, the video also demonstrates phase cancellation very well.
Getting back to the question of should you use linear phase EQ, admittedly some only use linear phase EQ in the audio mastering stage when it’s a single audio file and latency doesn’t matter.
That said, some engineers (and musicians) don’t like linear phase EQ because it removes what most consider to be a desirable coloration of the audio by way of some slight phase changes.
Many EQ plugins are based on analog hardware which imparts some color by way of how they work, so removing that component defeats the purpose for a lot of mixers.
Also note that not all EQ plugins will result in noticeable or unwanted phase issues.
A bad EQ will introduce phase issues with even small adjustments, whereas a GOOD EQ plugin will sound good or transparent regardless of the adjustments you’re making.
Part of why I love FabFilter’s Pro-Q 3 is how clean it operates on its default or standard setting.
It’s also rare and typically unnecessary that you should be using extreme EQ adjustments.
Smaller adjustments and wider adjustments by way of the Q setting sound much more natural than notching out specific sounds.
Typically if you find that you really need to roll up your sleeves and make a lot of sizable and specific adjustments to your audio, it’s not going to sound good regardless and you’re better off re-recording or replacing that audio if possible.
The TL/DR on linear phase EQ is that the “color” which is a result of small phase changes from most “normal” EQs is either too small to be noticeable, OR it’s actually desirable to the listener.
On the flip side, the latency issues associated with how linear phase EQs work to correct potential phase issues after cuts or boosts in frequencies isn’t worth the tradeoff or what you get from them.
