The Q in EQ
When I was first learning how music production worked, no one explained to me how Q worked, or even what it was. It remained this huge mystery to me for literally like a decade. So I thought it might be helpful to someone if I just quick wrote down a few little thoughts about it!
Q stands for “quality.” I can’t remember why, and it doesn’t matter. You can think of it as meaning “width.”
Q is measured on an inverse scale, where large numbers indicate a narrower width and smaller numbers indicate a wider width.
A Q of 0.6 is wide; 1.5 is medium; 4.0 is narrow; 10.0 is very narrow.
A good starting-out “rule” is to “boost wide, cut narrow.” This is a very helpful framework to start out with; it tends to be the most “invisible” or “natural-sounding” way to use EQ.
Doing a boost or a cut with a Q of 0.6 — that is, a wide boost or cut — is a good way to get a whole frequency region generally louder or quieter, in a very natural-sounding way.
A boost with a Q of 1.5 doesn’t sound like it’s that wide of a boost, but a cut of Q=1.5 sounds like it’s kind of a wide cut! Or, to phrase it differently, 1.5 is a pretty wide cut, but a fairly normal boost. Perception is a weird thing, and in this instance it’s always felt asymmetrical to me. A boost with a Q of 1.5 is nice for, say, the “bite” of a vocal (try 2300 Hz), or the air of a vocal (try 8000 Hz), or the meat of a guitar (try 700 Hz). 1.5 is a nice generic Q starting place for a boost.
“Boost wide, cut narrow” is a good starting place — but there can also be really good reasons for doing narrow boosts! I love doing a little poke with Q=3.0 somewhere between 1000-1800 Hz, to get a vocal to pop out of the mix in its own unique place. If I have two vocals I’ll pop one out at like 1200 and the other out at like 1600 and just let them each have their own little bit of definition. You don’t really hear it as an EQ change. Try +2 or +3 dB for this little trick. I’ll do the same thing on a kick drum somewhere between 80-120 Hz to get the thump or punch right where I want it; sometimes I’ll even tighten it up further to a Q of 4 or 5 if the punch feels like it’s not being specific enough.
Doing a cut with a Q of 10.0 or so is a great way to grab individual problem notes. You know how every bass guitar has that one note in the middle of the fretboard that’s louder than its neighbors? Try a Q=10 cut to get it evened out. (If you know what note it is, you can look up the exact frequency with a note-to-frequency calculator on the internet; much better than trying to guess!)
So far we’ve been talking about bell-shaped EQs, but other types of EQ have Q also!
On a shelving EQ, Q describes how abruptly or gently the shelf approaches 0 — larger numbers are gentler (i.e., a wider/longer transition), and smaller numbers are more abrupt (i.e., a narrower/quicker transition). Qs above 1.0 on a shelving EQ can cause a small excursion in the opposite direction on the other side of the center frequency, which can be cool for carving out a little space right above a shelving bump on, say, a kick or a rhythm guitar.
On a filter EQ — HPF or LPF — the Q acts to emphasize (add energy at) the cutoff point. Used subtly, this can help change the shape of a filter cut in a way that feels more harmonically extended and natural; used aggressively, this can make increasingly whistle-y harmonics that sound unnatural and very cool.
I would recommend opening up an EQ plugin that displays the curve visually, and going through each of these bullet points and recreating the curves. This will only take a few minutes, and will give you an even better understanding of the nuances of what I’ve described here!
Thank Q — jamie