What is clipping in audio?

Clipping in plain English

Every audio system has a loudest level it can carry. In a digital file that level is 0 dBFS, the biggest number the file has room to store. In an analogue circuit it's set by the voltage the circuit runs on. Ask for more than that and the system can't follow, so the top of the waveform stops at the limit and stays there until the wave comes back down. That flattened top is clipping.

The word comes from the picture: the peaks look as if someone took scissors to them. A clipped drum hit has a flat plateau where its sharpest spike used to be, and a heavily clipped sine wave starts to look like a square wave.

Two very different things go by the same name. Accidental clipping happens when a recording, a plug-in or an export runs out of room, and you don't get to choose how much is cut. Deliberate clipping uses a clipper plug-in to cut the peaks at a ceiling you set, by an amount you set, and it's one of the standard ways to make drums and masters louder. This page covers both, because the sound is the same and only the control differs.

Reading the lab

The four buttons along the top choose what happens to the sound: Dry, Soft clip, Hard clip or Limiter. Keys 1 to 4 do the same. The Drive knob turns the sound up before it reaches the clipper, so more drive means more of the wave tries to get past the ceiling.

The big screen shows the whole loop. The pale shape is the sound after the drive, before anything stops it, and the dashed lines are the ceiling at 0 dBFS. Everything shaded pink is the part that would go over, and the coloured shape in front is what actually comes out.

Under it, the left screen zooms in on 24 milliseconds around the loudest hit, close enough to see individual cycles. The dashed line is the input after drive and the solid line is the output, so this is where you see a peak turn into a plateau. The square screen in the middle is the transfer curve, which maps every input level to an output level: a hard clipper is a straight diagonal that stops dead at the ceiling, and a soft clipper bends away from the diagonal before it gets there.

The bottom screen measures the harmonics each clipper adds to a 110 Hz sine, whatever loop you're listening to. The panel on the right reads the current sound and tells you how much of it is going over, how far the crest factor has fallen and how much louder the result is at the same peak. Match loudness is on by default, so when you switch modes you hear the change in shape without a change in volume to sway you.

What causes clipping?

Clipping happens at whichever stage runs out of room first. Where that is decides whether it's already in your audio or can still be avoided.

While you record

A microphone or guitar goes through a preamp and then an analogue-to-digital converter. If the preamp gain is too high, the converter is asked for a level above 0 dBFS that it has no number for, and the top of the wave is cut flat. That clipping is written into the file. Turning the file down afterwards makes the flat tops quieter, but they stay flat.

24-bit audio has so much range below 0 dBFS, about 144 dB in theory, that there's no reason to record hot. Set the gain so the loudest moments of the take peak somewhere around −10 to −6 dBFS and you'll have room for the singer who suddenly belts the last chorus.

Inside the DAW

Ableton Live, Logic Pro, FL Studio and most other DAWs mix in floating point, a number format that can hold levels hundreds of decibels above 0 dBFS. A track meter going red inside the session usually means nothing has been cut yet. The exceptions are plug-ins that react to level on purpose, such as analogue models and anything with a clip stage, which will distort if you feed them too much.

When you export

This is where a red master meter turns into real clipping. A 16-bit or 24-bit WAV, like the converter, has nothing above 0 dBFS, so every sample over the line is cut when the file is written. A 32-bit float WAV can keep the overs, which makes it the safe format for stems you're sending to someone else to mix. Anything a listener will play needs to be under 0 dBFS, either because you turned the master down or because a limiter or clipper holds it there.

On playback

The highest sample in a file isn't always the highest point of the wave. When a converter joins the samples back into a smooth signal, the curve between two samples can rise above both of them. These true peaks can clip a converter that has no room above 0 dBFS. They also grow when a streaming service turns your file into MP3 or AAC, so the decoded version on a listener's phone can clip even though your meter never passed 0 dBFS. A hard-clipped master is especially prone to them, because the corners at the edges of each plateau make the rebuilt wave overshoot. The true peak lesson covers how to measure them.

What does clipping sound like?

That depends mostly on how long the sound stays over the ceiling. A snare's transient, the spike at the very start of the hit, lasts a few milliseconds. Clip 2 or 3 dB off it and the distortion is over before your ear can pick it out as a tone, so mostly you hear a slightly louder, slightly firmer snare. That's why clipping drums is so common.

A held note is the opposite. A sustained bass note or a vocal vowel sits over the ceiling for hundreds of milliseconds, and every cycle of it gets the same flat top. Your ear has plenty of time to hear the new frequencies as a buzz or a fuzz sitting on the note, and on a vocal it sounds like a cheap phone line.

The amount matters too. Push the drums in the lab from 6 dB of drive to 15 and the hits go from sounding a little denser to crunchy and papery, as the flat tops get longer and cover more of each hit.

Why does clipping add harmonics?

A pure sine wave is a single frequency. The only way to change its shape, whether by flattening it or rounding it, is to add other frequencies to it, and for a repeating wave those are always harmonics: whole-number multiples of the note. A 110 Hz note can gain harmonics at 220, 330, 440 Hz and on up.

Clipping that treats the top and bottom of the wave the same, which is what the clippers in the lab do by default, adds only odd harmonics: the 3rd, 5th, 7th and so on. With 9 dB of drive, a hard clipper puts the 3rd harmonic of the 110 Hz sine only 12 dB below the note. Turn the drive up to 15 dB and the 3rd comes up to 10 dB below the note, close to a square wave, whose 3rd harmonic sits 9.5 dB below the fundamental.

Clip one side of the wave harder than the other and even harmonics join in. The 2nd is an octave above the note and the 4th is two octaves up, so they blend in more easily than the odd ones and tend to sound fuller. Valve stages clip a little unevenly on their own, which is part of why people call them warm. The odd and even harmonics lesson goes further into how each one sounds.

Hard clipping and soft clipping

A hard clipper is about the simplest process in audio. Anything under the ceiling passes through exactly as it was, and anything over it comes out at the ceiling. On the transfer curve that's a diagonal line with a sharp corner where it meets the ceiling, and the corner is what makes the long row of high harmonics.

A soft clipper uses a curve that starts flattening before the ceiling and approaches it gradually, so the peaks come out rounded. It changes more of the sound than a hard clipper does, because even peaks below the ceiling get bent a little, but with no sharp corner its harmonics fade faster as they go up. With 9 dB of drive in the lab, the soft clipper's 5th harmonic sits 24 dB below the note, against the hard clipper's 21 dB, and by the 11th the gap has grown to about 20 dB.

Push a soft clipper hard enough and it behaves like a hard one; turn the drive past 18 dB in the lab and watch the curves close in on each other. For a side-by-side listen to both clippers and a limiter, all at matched loudness, read soft clipping vs hard clipping vs limiting.

Why does clipping make a track louder?

The loudness you hear follows the average level of a sound, its RMS. The loudness you're allowed to export is capped by its peak, because nothing can go over 0 dBFS. The gap between the two is the crest factor, and drums have a big one: a snare's transient can stand well above everything else in the hit while adding very little to the average.

Suppose a drum bus peaks at 0 dBFS and its loudest snare hits stand 4 dB above everything else in the loop. Raise the bus by 4 dB into a hard clipper with a 0 dBFS ceiling. The snare tips get cut back to where they were, while everything that stayed under the ceiling really is 4 dB louder. The clipper has traded 4 dB of peak for nearly 4 dB of loudness, and because the parts it cut lasted a few milliseconds each, they cost you very little.

The lab measures this on the real loop. With 6 dB of drive, the hard clipper cuts just 0.7% of the drum loop, yet its crest factor falls from 18.6 dB to 13.8 dB and it comes out 4.8 dB louder at the same peak. At 15 dB of drive it's 10.1 dB louder, but by then the hits sound crunchy. Watch those figures on the right while you change the drive, and use Match loudness to judge the result without the extra level.

Aliasing and oversampling

Digital audio can only hold frequencies up to half its sample rate, 22.05 kHz in a 44.1 kHz session. A clipper's harmonics carry on past it. Any harmonic above that limit can't be stored as itself, so it folds back down as aliasing: new tones at frequencies unrelated to the note.

Take a 5 kHz tone in a 44.1 kHz session and hard clip it. Its 5th harmonic should be at 25 kHz, which folds down to 44.1 − 25 = 19.1 kHz. The 7th, at 35 kHz, folds to 9.1 kHz, well inside the range you hear, and neither frequency belongs to the note. On bright sounds like cymbals and synth leads, aliasing makes clipping sound grainy and harsh in a way that has nothing to do with the clipping itself.

The fix is oversampling. The clipper runs internally at two, four or more times the session rate, so the harmonics have room to exist, then filters them off before converting back down. Most clipper plug-ins have an oversampling switch, and the sound you hear in this lab runs its clippers at four times the sample rate. The aliasing and oversampling lesson lets you hear the difference.

Clipping at each stage, and the fix

Clipper plug-ins

Any plug-in that cuts or rounds peaks at a set level is a clipper, whatever it's called. FL Studio ships with Fruity Soft Clipper. Ableton Live's Saturator has Analog Clip and Digital Clip curves, and Logic Pro has Clip Distortion. Among third-party plug-ins, SIR Audio Tools' StandardCLIP and Kazrog's KClip are made for clipping drums and masters, with oversampling and meters that show how much is being cut.

The controls are much the same from one to the next. Input or gain sets how hard you push the sound into the clipper, like Drive in the lab. The ceiling or threshold sets the level where clipping starts. A shape or knee control moves the curve between hard and soft, and an output control lets you match the level afterwards so you can compare fairly.

Some limiters have a clipper built in. The Maximizer in iZotope Ozone has a Soft Clip control that rounds the peaks just before its limiter, which is the clipper-then-limiter chain described below in a single plug-in.

How to use a clipper on drums, step by step

Drums are where a clipper earns its place, because their peaks are tall and short. The same method works on a single kick or snare.

1. Put the clipper on the drum busClip the drums on their own, before they meet the bass and the rest of the mix. That way a held sub note can't push the clipper into buzzing.
2. Turn on oversamplingTwo or four times is plenty on most material. It stops the harmonics folding back down as aliasing on the hi-hats and cymbals.
3. Raise the input until it clips 1 to 3 dBWatch the clipper's meter, or the pink shading in the lab, and stop when the loudest hits are losing 1 to 3 dB. Kicks and snares will be doing most of the clipping.
4. Choose the shapeA hard curve keeps the front of the hits sharp and adds some crunch. A soft curve sounds rounder and thicker. Try both at the same input level.
5. Match the level and compareTurn the output down until the clipped drums are as loud as the bypassed ones, then switch the clipper on and off. If you can't hear the difference, the loudness you gained cost nothing.
6. Push until you hear it, then back offRaise the input a decibel at a time until the snare starts to sound crunchy, then bring it back down by a decibel or two unless you want that crunch.

On a master, a clipper usually goes before the final limiter and takes the first 1 to 3 dB off the fastest peaks, which leaves the limiter less to do and less reason to pump. The limiting lesson covers the limiter that follows it.

Common clipping mistakes

Turning a clipped recording down to fix it

Lowering the level of a clipped take makes the flat tops quieter, but they're still flat, and the distortion is still there. A meter that now reads −6 dBFS doesn't mean the clipping has gone. Record it again, or use a de-clipping tool if you can't.

Clipping held notes

A clipper that sounds invisible on drums can wreck a vocal or a sub-bass, because a held note sits over the ceiling for its whole length. If the low end gets fuzzy when you push a clipper, take the bass off it or move the clipper to the drum bus. Clipping an 808 hard for its buzz is a different thing, because that's distortion you chose.

Leaving oversampling off on bright sounds

Without oversampling, clipping cymbals or a bright lead creates aliasing that sounds grainy and out of tune. If clipping makes the top end harsh in a way that doesn't sound like distortion, check the oversampling switch first.

Choosing by loudness

A clipped version at the same peak is louder than the original, and louder nearly always wins a quick comparison. Match the levels before you decide whether the clipping helped.

Hard clipping right at 0 dBFS on a master

A hard clipper set to 0 dBFS gives you samples at 0 dBFS and true peaks above it. If the clipper is the last thing on the master, set its ceiling lower or put a true peak limiter after it with its ceiling at −1 dBTP.

Training your ears to hear clipping

Light clipping on drums is hard to hear, which is the point of it, so the useful skill is telling one kind of peak control from another. The quiz under the lab plays the selected sound (the drums work best) through a soft clipper, a hard clipper or a limiter at matched loudness, with the screens covered, and asks which one it is. Listen to the front edge of each hit for grit, and to the quieter sounds just after each hit for ducking, which only the limiter causes.

Questions people ask

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