Use a low cut when the low end of a part shouldn't be there at all: rumble under a vocal, or the bottom end of a hi-hat. Use a low shelf when the low end belongs in the sound but there's too much of it, or too little, as on a bass that's a bit heavy or a kick that needs more weight.
If you're not sure, try the shelf first. A shelf cut that turns out to be too gentle is easy to deepen, while a low cut set too high takes the bottom out of every bass note and leaves the part thin.
At a glance
| Property | Low cut (high-pass) | Low shelf |
|---|---|---|
| What it does | Removes everything below the cutoff | Turns everything below the corner down or up |
| How deep it goes | Deeper with every octave, with no floor | Stops at the gain you set |
| Can it boost? | No | Yes |
| Main controls | Cutoff and slope | Frequency and gain |
| At its own frequency | 3 dB down | Usually halfway to its full gain |
| How it sounds | The low end has gone | The low end is quieter or louder |
| Best for | Rumble, handling noise, parts that don't need bass | Bass that's too heavy or too light, a boomy close-miked vocal |
What is a low cut?
A low cut is a high-pass filter with a friendlier name. Low cut says what it does to the sound and high-pass says what it lets through, which is everything above the cutoff. Ableton Live's EQ Eight, Logic's Channel EQ and FabFilter Pro-Q all label it Low Cut. A mixing console calls the same thing a high-pass filter, HPF for short, and plenty of microphones and audio interfaces have a low-cut switch that puts one in front of the recording.
It has two controls that matter. The cutoff is where it starts, and at that frequency the sound is 3 dB down. The slope, in decibels per octave, is how quickly it falls from there: a 12 dB per octave low cut at 100 Hz is 12 dB down at 50 Hz, about 24 dB down at 25 Hz, and keeps going. There's no gain knob, because a low cut can only take sound away. Its depth comes from the slope and from how far below the cutoff you are, and it never levels off.
Some low cuts have a Q or resonance control as well. Leave it at about 0.7 for mixing; higher settings add a bump just above the cutoff, which the filter resonance lesson covers.
What is a low shelf?
A low shelf turns everything below its corner frequency up or down by the same amount, the way the bass knob on a stereo does. Its controls are a frequency and a gain. Set it to −6 dB at 100 Hz and the curve slopes down through 100 Hz, then flattens out at 6 dB down and stays there, right to the bottom of what you can hear.
That flat floor is what separates it from a low cut: below the slope, every part of the low end keeps the same balance as before, just quieter. And because it has a gain control, it can go the other way: the same band at +4 dB makes the kick and bass heavier, which no low cut can do.
The shelf EQ lesson covers high shelves too, along with the shelf shapes different EQs use.
Reading the lab
The lab is set up with just the two bands. Band 1, the amber point, is the low cut at 100 Hz, and it starts switched off. Band 2, the pink point, is the low shelf, parked at 200 Hz and 0 dB until step 3 moves it to the same frequency as the cut. Their types are locked, so band 1 is always the cut and band 2 always the shelf, and you can move either by dragging its point or with the knobs underneath.
The pink line on the big screen is the EQ curve and the teal shape behind it is the spectrum of what's coming out. Hover anywhere on the screen and it tells you how many decibels the curve takes off at that frequency, which is the quickest way to see where the two shapes part. The Right now panel measures the loop itself, so it'll tell you how much of the sound's energy sits in the range each band works on. A/B switches the EQ off and matches the level, so a cut doesn't lose the comparison just for being quieter.
Of the sounds, the bass loop and the full mix have the most low end. The drum loop has very little below 100 Hz, and the vocal has almost nothing below 150 Hz, which makes them good for hearing how little a low cut changes when there's nothing down there to remove.
Where the two curves part
Put a low cut and a low shelf at the same frequency and they look alike for the first octave. A 12 dB per octave low cut at 100 Hz is 12.3 dB down at 50 Hz, and a shelf cutting 12 dB at 100 Hz is 11.1 dB down there. On a part with nothing below 50 Hz they'd sound almost the same.
Below that, they split. The low cut keeps falling, roughly another 12 dB for every octave, and it's 28 dB down by 20 Hz. The shelf has stopped at 12 dB. In the full mix, the lowest bass notes sit around 41 Hz, which is where the gap opens up: 15.6 dB down through the low cut against 11.6 through the shelf.
| Frequency | Low cut, 12 dB/oct | Low cut, 24 dB/oct | Low shelf, −6 dB | Low shelf, −12 dB |
|---|---|---|---|---|
| 200 Hz | −0.3 dB | 0 dB | −0.4 dB | −0.9 dB |
| 100 Hz | −3 dB | −3 dB | −3 dB | −6 dB |
| 50 Hz | −12 dB | −24 dB | −5.6 dB | −11 dB |
| 41 Hz | −16 dB | −31 dB | −5.8 dB | −12 dB |
| 20 Hz | −28 dB | −56 dB | −6 dB | −12 dB |
At 100 Hz, a 6 dB shelf and a 12 dB per octave low cut are both 3 dB down, and by 200 Hz both are under half a decibel. Everything that makes them sound different is below the frequency you dialled in. So if a low cut at 100 Hz sounds too thin, most of what you're missing is below about 60 Hz, and moving the cutoff down a little usually fixes it.
The frequency knob means different things
On a low cut, the frequency is the cutoff, where the sound is 3 dB down. Almost every filter you'll meet follows that rule.
Shelves are less consistent. In this lab, as in the Web Audio standard it's built on, a shelf's frequency is where it has reached half its gain in decibels, so a −12 dB shelf at 100 Hz is 6 dB down at 100 Hz and is within half a decibel of its full depth only below about 40 Hz. Other EQs put the shelf frequency somewhere else on the slope, so 100 Hz on one plug-in's shelf can sit noticeably higher or lower than 100 Hz on another's. Treat the number as a starting point and look at the curve, or listen, to find where the shelf really begins.
Some EQs also give their shelves a Q control. Turning it up makes the slope steeper and adds a small bump in the other direction just past the corner. This lab's shelves have a fixed, gentle slope with no bump.
Low cut and low shelf on a bass
Low notes are where choosing wrong costs the most. Every note has a fundamental, the frequency you hear as its pitch, plus harmonics at two, three and four times that frequency. The lowest notes in the bass loop have fundamentals around 41 Hz, which puts their second harmonic at 82 Hz and their third at 123 Hz. On this loop, nearly a quarter of the energy sits below 60 Hz.
A 12 dB per octave low cut at 80 Hz takes those 41 Hz fundamentals down by 12 dB and the 82 Hz harmonic by only 3. Your ear still works out the pitch from the harmonics, so you can hear which notes are playing, but the bottom of each note has mostly gone and the bass sounds small. On a big system you'd lose the part you feel.
A low shelf cutting 4 dB at 80 Hz brings the 41 Hz fundamentals down by 3.7 dB and the 82 Hz harmonic by 2. The balance inside each note barely changes, so the bass sounds like the same bass, a little lighter. That's nearly always what you want when a bass is too heavy in the mix.
The same goes for a kick drum, whose weight lives between about 40 and 100 Hz. When a kick and a bass fight, the answer is usually a shelf or a bell on one of them, or sidechain ducking, and seldom a low cut that removes the bottom of either. The kick and bass lesson covers that.
Boosting the low end, and guarding the boost
A low cut has no way to make the bass louder. If a mix needs more weight, it's a job for the shelf. On the full mix, a low shelf at +4 dB and 100 Hz is 2 dB up at 100 Hz and the full 4 dB from about 30 Hz down, and the loop comes out 0.7 dB louder overall.
That boost doesn't stop at the bass notes. The shelf lifts everything below its corner by the same amount, including sub-bass under 30 Hz that most speakers can't play, plus any rumble or mic-stand thumps. You may not hear them get louder, but your meters will, and they eat into your headroom.
The usual fix is to use both bands. Put a low cut well below the music, around 25 to 35 Hz, under the shelf boost. With a 24 dB per octave cut at 30 Hz and the +4 dB shelf at 100 Hz, 41 Hz still comes up 3.5 dB, but 25 Hz is 3 dB down and 20 Hz is 10 dB down.
The full mix in the lab has almost nothing below 30 Hz, so on this loop the low cut changes very little you can hear. Switch to pink noise and repeat the last two steps to see what it does to a sound that has energy all the way down. The Pultec EQP-1A, a valve EQ from the 1950s, has a related move built in: its low boost and its low attenuation share one frequency switch, and engineers often turn both up at once. The Pultec low-end trick lesson explains what that does to the curve.
Phase, and why a low cut can raise your peaks
Both bands in this lab are minimum-phase filters, the normal kind used in most EQs. Alongside the change in level, they shift the timing, or phase, of the frequencies around their corner. A 12 dB per octave low cut shifts the phase by 90 degrees at its cutoff, a 24 dB one by 180 degrees and a 48 dB one by a full 360. A shelf shifts it too, by less, and only around its slope.
You rarely hear that as a sound of its own, but it can change the shape of the waveform. The full mix in the lab has under 1% of its energy below 30 Hz, and the lab sets its highest peak to −0.9 dBFS. Put the 24 dB per octave low cut at 30 Hz from step 7 on it, without the shelf, and the average level moves by less than 0.1 dB, yet the highest peak rises by about 0.8 dB, to just under 0 dBFS. The filter removed almost nothing and still shifted the parts of the wave against each other in time.
So check what's actually below the cutoff before you cut, and keep an eye on your peaks after a low cut on something already limited. If you need to cut low end without any phase shift, a linear-phase EQ can, at the cost of delay and some pre-ringing; the linear-phase vs minimum-phase lesson compares them.
Low cut or low shelf for common sounds
These are starting points. The slope and the exact frequency depend on the recording, and on what else is playing in that range.
| Source | Low cut | Low shelf |
|---|---|---|
| Lead vocal | 80–120 Hz, 12 or 24 dB/oct | −2 to −4 dB around 200 Hz if it's boomy |
| Acoustic guitar | 60–100 Hz | −2 to −4 dB around 150–200 Hz for body boom |
| Kick drum | Only under the music, 25–35 Hz | ±2 to 4 dB at 60–100 Hz |
| Bass | Only under the music, 25–35 Hz | ±2 to 4 dB at 60–120 Hz |
| Pads and keys | Gentle, 80–150 Hz, if the bass needs room | −2 to −6 dB at 150–250 Hz |
| Hi-hats and cymbals | 200–400 Hz | Rarely needed |
| Full mix or master | Gentle, 20–30 Hz, if there's rumble | ±1 dB to rebalance |
The vocal row has both for a reason. A low cut clears rumble and handling noise below the voice, and a shelf deals with proximity effect, the extra bass a directional microphone picks up when the singer is close to it. Cutting the boom with a low cut set high enough to reach 200 Hz would take the chest out of the voice as well.
How to choose between a low cut and a low shelf, step by step
- Listen to the low end on its ownSolo the range, with the lab's range strip or your EQ's band solo, and listen through a few bars. Rumble or near silence means a low cut is safe. If what you hear is the bottom of the notes, you want a shelf.
- For a low cut, raise it until the part thinsStart at 20 Hz with a 12 or 24 dB per octave slope and sweep it up while the whole mix plays. When the part starts to sound smaller, back it off a little, say from 120 Hz to 90 Hz.
- For a shelf, start with 3 dBSet the frequency near where the excess seems to begin, cut or boost 3 dB, and adjust in 1 dB steps. A shelf move bigger than about 6 dB usually means a bell or a low cut would fit the job better.
- Check the bottom octaveHover over the curve, or look at your EQ's display, at 30 to 40 Hz. That's where the two shapes differ the most, and it's what you'll hear on a big system and miss on a laptop.
- Compare at matched loudness in the mixFlip between them with A/B, or your EQ's bypass with the output gain set to match. Both take level away, by different amounts, and the louder of two versions tends to win just for being louder.
Common mistakes
Low-cutting the bass to tidy it
A low cut at 80 or 100 Hz on a bass line takes most of the bottom out of every low note. If the low end of the mix is too heavy, a shelf cut of a few decibels does the job and leaves the notes whole.
Using a shelf to remove rumble
A 6 dB shelf cut leaves the rumble only 6 dB quieter, still there on the meters and on any system that plays it. For something you want gone, use a low cut.
Setting the low cut from a chart
Putting a low cut at 100 Hz because a chart said so ignores what's in the sound. On the vocal loop in this lab there's almost nothing below 150 Hz, so a cut there changes very little; on a deep male voice the same setting would thin the bottom of the voice. Sweep it and listen.
Boosting with a shelf and forgetting the sub
A +6 dB low shelf adds 6 dB to everything below its corner, including the frequencies you can't hear on your speakers. Check the mix on headphones or a system with a sub, or add a gentle low cut under the boost.
Stacking low cuts on every track
Each low cut takes a little warmth from a part. Across thirty tracks, steep cuts at 150 Hz add up to a thin mix with a gap between the bass and everything else, so use them where there's something to remove.
Training your ears
The best exercise for this comparison is step 4 and step 5 on the bass loop: flip band 1 and band 2 on and off until you can tell, with your eyes closed, whether the notes have lost their bottom or just got quieter. Then do the same on the acoustic guitar, which has its body around 200 Hz and very little below 100.
The quiz under the lab works on a related skill. It boosts one of five frequency ranges by 9 dB, covers the screens and asks which range it was. Knowing by ear where the bass ends and the low mids begin is what tells you where a low cut or a shelf should go in the first place.
Questions people ask
Is a low cut the same as a high-pass filter?
Yes. Low cut describes what it does to the sound and high-pass describes what it lets through, so the two names mean the same filter. Ableton Live's EQ Eight, Logic's Channel EQ and FabFilter Pro-Q all call it Low Cut; consoles and older manuals tend to say high-pass filter, or HPF.
Is a low shelf a filter?
Technically, yes, because any EQ band changes the level differently at different frequencies. In a studio, though, people say filter for the types that remove a range, like the low cut, and call a shelf an EQ band, because it turns a range down or up by an amount you choose and then stops.
What frequency should I low-cut a vocal at?
Start around 80 to 100 Hz with a 12 or 24 dB per octave slope, then raise it until the voice starts to thin and back it off a little. A deep male voice may need it lower, around 60 to 70 Hz, and a high voice can take more.
Should I put a low cut on every track?
No. Cutting the low end of parts that don't need it clears space, but a steep cut at 150 Hz on everything leaves a thin mix, because the warmth of each part adds up. Use a low cut where there's rumble or nothing musical down there, and a low shelf where the part just has a bit too much.
Does a low shelf boost cause problems?
It can. A shelf lifts everything below its corner, right down to 20 Hz, so any rumble or sub-bass the speakers can't play gets louder as well and uses up headroom. Putting a gentle low cut at 25 to 35 Hz under the boost stops that.
Why does my low cut make the peaks louder?
Because a low cut shifts the phase of the frequencies near and above it, which moves the parts of the wave against each other in time. On a mix that's already been limited, the peaks no longer line up the way they did, so the highest one can rise even though the sound is quieter on average. A 30 Hz low cut on the full mix in this lab raises its highest peak by 0.8 dB.