If you’ve been out and about on the internet then you’ve probably read that subtractive EQ is generally better than additive EQ. In other words, it’s better to attenuate than to boost.
And you have probably read all sorts of reasons for this: less phase shift, sounds smoother, more accurate, doesn’t require active gain, etc.
Well, I’m here to tell you that a great deal of that is false. Let’s start by dispelling a few myths.
Myth #1: Subtractive EQ incurs less phase shift, or less noticeable phase shift
This is untrue. The degree of phase shift is 100 percent controlled by the amount of cut or boost. In fact “phase shift” is almost synonymous with “equalization.” They are inherently part of the same process.
Now, are the artifacts of said phase shift less noticeable? In objective technical reasoning, no, they are not.
And here’s why: If you exclusively use boosting to create an EQ curve on a source and then recreate the exact same curve using only attenuation, and then level match those two outputs exactly, you will get identical signals.
A simple way to test this is by taking any sound source and a shelf filter. Mult the sound source. On one, use a hi-shelf to boost up some high end. On the other, use a low shelf, set to the same corner frequency with the same slope and attenuated by the same amount. Then boost the output volume of the low-shelfed signal up to match the hi-shelfed signal and flip the phase. They will completely null.
What’s important, is to use an EQ where the parameters match up equally. For example, this will work with the Waves Q EQ, but will not work with the Waves Ren EQ.
What this demonstrates is that the phase shift and artifacts produced by that shift are based on the curve and degree of equalization, not whether the equalization is positive or negative.
Myth #2: Subtractive EQ sounds smoother
Ultimately the truth to this is based more on application than reality. It tends to be easier to mix additively – boosting up things you want more of.
The problem with this is that it leads to a lot of compensational boosting. By that I mean boosting up lots of frequency ranges when really we just wanted to hear less of one frequency range.
Or we will boost up a frequency because we aren’t hearing enough of it, when in reality there’s something from another instrument that’s getting in the way.
These issues aren’t inherent to additive or subtractive EQ, rather, they stem from using additive EQ when subtractive EQ would be a better approach.