Reach for a filter when you want part of a sound gone, like the rumble under a vocal or the hiss on an old sample. Reach for an EQ band, a shelf or a bell, when you want a range louder or quieter but still there.
The quickest test is the edge of the curve. If it keeps falling, it's a filter. If it flattens out at a fixed number of decibels, it's EQ.
At a glance
| Property | Filter (high-pass, low-pass) | EQ band (shelf, bell) |
|---|---|---|
| What it does | Lets one side of the cutoff through and removes the other | Turns a range up or down |
| How deep it cuts | Deeper with every octave past the cutoff | Only as far as the gain you set |
| Can it boost? | Only a bump at the cutoff, using resonance | Yes |
| Main controls | Cutoff, slope, resonance | Frequency, gain, Q |
| How it sounds | That range is gone | That range is quieter or louder |
| Usually moving? | Often, on synths and in DJ sets | Mostly set and left |
| Best for | Rumble, hiss, sweeps, synth tone | Balance, and making room between parts |
Is an EQ a filter?
Technically, yes. To an engineer, a filter is anything that changes the level of a sound differently at different frequencies, and by that definition every band on every EQ is one. The lab on this page shows it. Each of its bands is made from Web Audio's biquad filter, a small piece of maths that can be set up as a high-pass, a low-pass, a shelf, a bell or a notch. Those shapes come from one set of formulas, written up by Robert Bristow-Johnson in what's usually called the Audio EQ Cookbook, and many plug-in EQs start from something similar.
In a studio, though, the two words mean different things. When producers say filter, they mean the types that pass one part of the spectrum and remove the rest: high-pass, low-pass, band-pass and notch. When they say EQ, they mean the bands that turn a range up or down by an amount you choose: shelves and bells. Most EQ plug-ins contain both kinds, and that's where the confusion starts. This page uses the studio meaning, and the EQ lesson covers every band type in more detail.
Reading the lab
The lab is set up with one of each. Band 1 is a high-pass filter and band 5 a low-pass, and both start switched off. Between them sit band 2, a low shelf, then a bell and a high shelf, all at 0 dB. The pink line on the big screen is the EQ curve, and the teal shape behind it is the spectrum of what comes out.
The lesson steps under the lab put a filter and an EQ band side by side at the same frequency, so you can hear the difference and see it in the shape of the curve. Hover over any point on the screen to read how many decibels the curve takes off there. The Right now panel measures the loop itself, so it'll tell you, for example, how much of the sound's energy sat below a filter's cutoff. A/B switches the whole EQ off at matched loudness.
Where a cut stops
This is the difference you can see. Put a high-pass filter and a low shelf at the same frequency, set them to roughly the same depth one octave down, and their curves start out almost on top of each other. Then they split.
A 12 dB per octave high-pass at 150 Hz is 3 dB down at its cutoff and 12 dB down an octave lower, at 75 Hz. It doesn't stop there. At 40 Hz it's 23 dB down and at 25 Hz it's 31 dB down, because the slope takes roughly another 12 dB for every octave you go down, so the very bottom of the spectrum ends up close to silent.
A shelf cutting 12 dB at the same 150 Hz is 6 dB down at 150 Hz, because in this lab, as on many EQs, a shelf's frequency is where it has reached half its gain. At 75 Hz it's 11 dB down, close to the filter. At 40 Hz it's 12 dB down, and at 25 Hz still 12 dB, so the curve has gone flat. The shelf took the low end down by a fixed amount and kept all of it.
| Frequency | High-pass, 12 dB/oct | High-pass, 48 dB/oct | Low shelf, −12 dB |
|---|---|---|---|
| 150 Hz | −3 dB | −3 dB | −6 dB |
| 75 Hz | −12 dB | −48 dB | −11 dB |
| 40 Hz | −23 dB | −92 dB | −12 dB |
| 25 Hz | −31 dB | −125 dB | −12 dB |
You can hear that split on the full loop. Through the filter, the kick loses its weight and the bass line turns into a thin outline. Through the shelf, both are smaller, but the deepest part of the kick is still there underneath. On speakers that play sub-bass, the shelf sounds like the same mix with the bass turned down and the filter sounds like the bass has left the room.
Steepen the filter and the gap gets bigger. At 48 dB per octave the same 150 Hz high-pass is 48 dB down at 75 Hz, while the deepest any shelf in this lab can go is 18 dB, the limit of its gain control. The filter slopes lesson covers how to choose between gentle and steep.
The top end works the same way. A 12 dB per octave low-pass at 6 kHz is 15 dB down at 12 kHz and 25 dB down at 16 kHz, while a high shelf cutting 12 dB at 6 kHz stops at 12 dB. For the low-end version of this choice in detail, read low cut vs low shelf.
Only EQ can boost a range
A high-pass or low-pass filter has no gain control. It can only let things through untouched or turn them down, so if a vocal needs more air or a kick needs more weight, a filter can't help. An EQ band can go either way, and the same low shelf that cut 12 dB a moment ago can lift everything below about 100 Hz by up to 4 dB.
The one exception is resonance. Raise the Q on a filter and it adds a bump just before the cutoff, which is a boost of sorts, but it's narrow and it sits right next to the part being removed. It's a different tool from a shelf or a bell, and it's mostly used on synths.
Filters as effects: sweeps and resonance
A mixing EQ is usually set once and left alone. Filters are often moved while the music plays, and that's when they stop being a clean-up tool and become an effect.
On a synth, the filter is the main tone control. A subtractive synth starts from a bright waveform full of harmonics, and a low-pass filter takes the top off it; the Moog ladder filter, for example, is a 24 dB per octave low-pass. Its cutoff is usually moved by an envelope, so each note starts bright and closes down, or by an LFO, so the tone wobbles. The filter envelopes lesson shows how that works.
Resonance is what makes those moves sound like a synth. With the Q on band 5 raised to 4, the low-pass at 1 kHz has a 12 dB peak right at the cutoff and falls to 23 dB down by 2 kHz. Drag the point while the chords play and the peak picks out different overtones as it goes, which gives the sound a vowel-like, wah quality. The filter resonance lesson goes further, up to the point where the filter starts to whistle on its own.
DJs use the same idea on whole tracks. Many DJ mixers give every channel both: a three-band EQ for balancing one track against another, and a single filter knob that runs a low-pass one way and a high-pass the other, used for builds and transitions. In a DAW, Ableton Live's Auto Filter and Logic's AutoFilter are filter effects with an LFO and an envelope built in to move the cutoff for you.
Band-pass: two filters together
Switch on a high-pass and a low-pass at once and you get a band-pass, which keeps the stretch between them and removes everything either side. With a 24 dB per octave high-pass at 300 Hz and a low-pass at 3 kHz, 150 Hz is 24 dB down and 6 kHz is 26 dB down, and by 12 kHz the low-pass alone has taken off 56 dB. On a vocal, that's roughly the telephone sound.
EQ bands can't make that effect. A bell boosting the middle turns it up but leaves the lows and highs at full level, and a pair of shelves cutting 18 dB still leaves both ends audible.
When to use a filter and when to use EQ
| Job | Use | Why |
|---|---|---|
| Rumble under a vocal or guitar | High-pass at 80 – 120 Hz | Nothing useful lives down there, so remove it |
| Bass a little too heavy | Low shelf, −2 to −4 dB | Turns it down and keeps the sub |
| Mud in the low mids | Bell cut at 200 – 400 Hz | Leaves the bass below it alone |
| Hiss on an old sample | Low-pass, set by ear | The hiss goes along with the top end |
| Cymbals a bit too bright | High shelf, −2 to −6 dB | They sit back and keep their top end |
| More air on a vocal | High shelf, +1 to +3 dB | A filter can't boost |
| A build into a drop | Automated high-pass or low-pass | A moving cutoff is the effect |
If the part isn't supposed to be there, filter it. If it's supposed to be there but the balance is wrong, EQ it. Rumble under a vocal and the low end of a hi-hat are things the mix doesn't need, so a high-pass is the right tool. A kick that's a bit too boomy, or hats that are a bit too bright, still need those ranges, just less of them.
The top end is where people reach for a filter when a shelf would do better. A low-pass at 6 kHz on a drum loop makes the cymbals sound as if they've moved behind a curtain, because everything from 12 kHz up is heavily cut. A high shelf cutting 6 dB at the same point is about 3 dB down at 6 kHz and close to 6 dB down above that. The hats sit back, but they keep their shape.
How to choose between a filter and a shelf, step by step
- Name what you hearRumble or hiss you don't want is a job for a filter. A range that belongs in the sound but is too loud, such as boom or brightness, is a job for EQ.
- Listen to what you'd removeSolo the range with the lab's range strip or the Listen to this band button. If there's nothing musical in it, a filter is safe.
- Try the filter first on the low end of non-bass partsRaise a 12 dB per octave high-pass until the part starts to thin, then back it off a little.
- Try a shelf where the part needs its lows or highsStart with a 3 dB cut and change it in steps of 1 or 2 dB.
- Compare in the mix at matched loudnessFlip between the two with the rest of the track playing, using A/B, or your EQ's bypass with the output gain set to match.
Common mistakes
Using a low shelf to remove rumble
A 6 dB shelf cut at 100 Hz still leaves the rumble at 30 Hz, only 6 dB quieter, and it keeps using up headroom on the master. If you want it gone, use a high-pass.
Filtering the bass out of everything
High-passing every track at 150 Hz with a steep slope clears the low end and then leaves the mix sounding thin, because each part loses a little warmth and the losses add up. A gentle shelf, or a lower filter, is often enough on pads and keys.
Low-passing to tame harshness
Harshness usually sits in a band somewhere around 2 to 5 kHz. A low-pass set low enough to reach it takes all the air away too, whereas a bell cut at the harsh frequency fixes it and keeps the top.
Leaving resonance up on a mixing filter
A high-pass on a vocal with its Q above 1 adds a bump just above the cutoff, which can make the voice boomy right where you were trying to clean it up. On mixing filters, leave the Q at about 0.7, where there's no bump.
Training your ears
The fastest way to learn the difference is to go back to step 3 and flip between the two bands: switch band 2 off, select band 1 and switch it on, then swap back. Do it on the bass loop and the pink noise as well as the full mix. The quiz under the lab works on a related skill. It boosts one of five frequency ranges by 9 dB, hides the screens and asks which one it was, and knowing where bass, mids, presence and air sit is what tells you where to put a filter or a shelf in the first place.
Questions people ask
Is a high-pass filter part of an EQ?
On most mixing EQs, yes. Ableton Live's EQ Eight and Logic's Channel EQ both have low cut and high cut bands, which are high-pass and low-pass filters. They sit next to the shelves and bells and switch on the same way, but instead of a gain control they give you a choice of slope.
Is a low cut the same as a low shelf?
No. A low cut is a high-pass filter, which keeps cutting further the lower you go. A low shelf cut turns everything below its corner down by the amount you set, say 6 dB, and stays at that amount right down to 20 Hz.
Can I boost with a filter?
Only at the cutoff, using resonance. Raise the Q on a high-pass or low-pass and it adds a bump just before it starts cutting. That's useful on synths and occasionally on a kick or bass, but to lift a whole range, use a shelf or a bell.
What is a filter in music?
In music production a filter usually means a high-pass, low-pass, band-pass or notch: a process that lets one part of the spectrum through and removes another. On a synth the filter is the main tone control, and its cutoff is often moved by an envelope or an LFO while the note plays.
Which is better for cleaning up mud, a filter or EQ?
EQ. Mud lives in the low mids, around 200 to 400 Hz, which is also where the body of most instruments sits. A bell cut of 2 to 4 dB there leaves the low end underneath alone, while a high-pass set high enough to reach the mud would remove the bass as well.
Do filters and EQ sound different?
Only because they make different curves. Inside most EQ plug-ins the high-pass and the shelf are built from the same maths. A cut that stops at a fixed depth sounds like the same instrument with less of one range; a cut that keeps going sounds like that range has been taken away.