High-cut EQs: shelf vs LPF, normal vs linear phase
Hi everyone! At long last, Shannon and I are back from our fall tour. It was a full-on couple of months, but it went great! I think we’ve accomplished everything we set out to accomplish this year in that corner of our world, and I’m happy about it.
I’ve missed my Jamie’s list diy crew very much, and I’m very excited now to be getting back into studio season, which coincidentally is also Jamie’s list season! So without further ado … let’s talk about high-cut EQs.
Sometimes when you’re fine-tuning the EQ on a song, there’s a bit too much very high end. You know how sometimes the high end is just too … much? Here are a couple of strategies for dealing with that!
First question: we need to decide whether we want a) somewhat less of the highest frequencies or b) to totally get rid of them.
If the former, I use a shelving EQ; sometimes a high shelf placed way toward the top of the frequency range can help me focus in on exactly the right amount of that sizzle and sheen. I usually start with my frequency at like 15000 Hz or so, put the gain at -3 dB or so, and then sweep the frequency and gain around until I find a combination that feels right. For example, the song I’m mastering at the moment benefitted from a high shelf at 16480 Hz, -7 dB. Just smoothing things out up there.
If on the other hand I want to totally get rid of the very highs above a certain point, then that’s usually more of a lowpass filter situation. How steep to set the slope of the filter is a big question, and in my experience it’s completely situational; I usually start at 12 dB/oct and then adjust if and as the situation dictates. If I want to gently roll off the high end, then that might be more of a 6 dB/oct LPF situation … if I want to severely and surgically chop off some ultrasonic garbage, then I might go very steep, perhaps even 36 or 48 dB/oct.
Something you’ll notice sometimes with LPFs is that they can almost enhance the top end a bit — make it shinier, sort of? This is because lowpass filters introduce phase shift, which can have the effect of sort of “smearing” the sound in the range below the LPF’s corner frequency.
Sometimes this smear is great! It can really help shift the excitement in the high end downward, by adding phase shift gooeyness and shimmer below the cutoff frequency as you simultaneously cut frequencies above the cutoff frequency. This can take esses, tees, breathy “air,” etc from an annoying “sonic garbage” place to a much cooler “high-end sheen” kind of place.
But sometimes the LPF phase shift smear is decidedly not helpful. You can tell! It’ll rub you the wrong way when you put the LPF on — like the sound is wrong. If this is the case, then that’s when I try using a linear phase EQ instead of a normal EQ.
Linear phase EQs do not impart phase shift to the sound they’re EQing — that’s what “linear phase” means. There are tradeoffs, which manifest in the time domain — linear phase EQs can cause pre-ringing, which is exactly what it sounds like, like a little whoosh before each note — and this can be problematic in the lower frequencies — but you can’t really hear it most of the time in the high frequencies.
This essentially means that you can use linear phase EQs to make sonically invisible cuts or boosts, without changing the character of the high end! And sometimes that’s the perfect solution.
Here are some ways that I think about how to decide whether to use normal (phase-shift-y) EQ or linear phase EQ for high cuts:
I will typically reach for a linear phase EQ when I’m in love with the character of the high end, and just want less (or more) of it loudness-wise.
I most often just start with a normal EQ — and if it seems like it’s messing up the sound in the top end, then I try a linear phase EQ.
If I want the top end smeared more — maybe it’s too clean, not shiny-special enough — I’ll use a normal EQ.
If I want to preserve the detail in the high end, I’ll use a linear phase EQ.
It’s worth noting that most every EQ is made a little bit differently, so it’s worth trying some different ones with the same settings once you’ve figured out roughly what settings you want, just to see if you prefer the sound of one over the others. Some are gooier, some are sweeter, some are warmer, some are airier — there are lots of different potential EQ characteristics. Sometimes the differences can be striking.
Your cutoff, pal — jamie