Linear Phase EQ ExplainedMarch 28, 2012
Have you ever use an EQ on your mix only to find out that it introduced some phasing issues to your track? So what do you do when this happens? Well you break out your trusty linear phase EQ that's what. This week we are going to cover the linear phase explained.
WHAT IS AN LINEAR PHASE EQ ANYWAY?
I am sure that you have heard the term linear phase equalizer being used and have wondered what it was and what it really does, but more importantly do you need one in your production toolbox? So let's start with what a linear-phase EQ is. When you are using a minimum phase EQ (this is the equalizer most used in a production setting) and you decide to make a cut or a boost with that EQ, you may have some alteration to the sound.This alteration is a phase delay of the frequencies that you are boosting and/or cutting. This becomes audible artifacts or better known as smearing. In most situations this phasing can not but heard, but in a situation where it can and you don't want that phasing then you may what to introduce a linear phase EQ to address the problem. A linear-phase EQ will make it so that this phasing that can be present in your music will be removed or better yet masked so that you can no longer hear it.
(The above screen capture shows the difference between a linear phase EQ and a minimum phase EQ (in this case FL Studio's Parametric 2 EQ)
HOW DOES IT DO THAT?
Well I won't give you the nerdy long and boring explanation of what a linear-phase EQ does. Instead I will give you the short and concise version. A linear-phase EQ eliminates phasing by time shifting the frequencies (all the frequencies) so that the phase is not heard. In simple terms it will delay your signal so that all the frequencies within the track are kept in phase.
IS THIS BAD?
Well all linear phase equalizers will introduce some major latency issues to your song. See this time shifting that a linear-phase EQ does causes a delay in the sound. Yes you will lose any phasing at the frequency points that you EQ (and surrounding affected frequencies), but you will also have an issue with transient smearing as a trade off. This is not always a good trade and in my option this smearing makes the track sound plastic like.
WHY NOT USE THIS ALL THE TIME?
In most cases it would be unnecessary because the audible artifacts that you get from a minimum phase EQ won't be detected in your track anyway. Secondly it is not an “all the time tool” but more of a specialty tool that can work along side your other production tools. As a matter of fact there are even some minimum phase EQ's that can be switched over from minimum to linear-phase on the fly.
Linear-phase equalizers are mostly used in a mastering setting as most mastering houses will have a Weiss EQ1-LP somewhere in the building. This does not mean that a linear-phase EQ can only be used in mastering situations only, but it does mean that in most cases a linear-phase EQ is going to be used sparingly instead of being used on every track of a song where an equalizers is needed.
I personally do not use a linear-phase EQ often, but in most cases I find that I use one to handle sub frequencies on tracks I am asked to mix. Sometimes I run into a muddy mix down there (very low frequencies) that my client could not hear on their system that needs to be cleaned up. In these situations I find a linear-phase EQ to be just what is needed for the job.
SO DO I NEED A LINEAR PHASE EQUALIZER?
Well I can not answer that question for you because I don't know all your needs. But I can tell you that if you don't already have and use one that you may not need one. If you do decide that you need a linear-phase EQ to fill your production toolbox then you can choose a dual purpose EQ that works as a minimum phase as well as a linear-phase EQ. Or you can choose from the many freebies that are out there. Filtrate LE and Cockos' ReaFIR are two of my favorite free linear-phase EQ plugins. Download one of them and try it out for yourself.
A linear phase EQ is one of the most mis-understood audio effects out there. I won't pretend to think that this article explained it all to you. Or that I am all-knowledgeable when it comes to all the inter workings of the linear phase EQ. There is a lot to learn about this little gem of the studio. I would recommend that you try out a demo or grab a freebie and just start experimenting with it.
Stay tuned for more weekly tips and tutorials every Wednesday.
Article written by Alex Butler
Alex is an audio engineer, studio producer and freelance writer based out of Seattle, WA.