What is distortion?

Distortion in plain English

A clean amplifier, or a clean plug-in, gives you back a bigger or smaller copy of exactly what you put in. Draw the input waveform and the output waveform and they're the same shape. Distortion is what happens when a circuit bends that shape. The usual cause is level: every circuit and every plug-in curve has a point past which it can't get any louder, and once the peaks of a sound reach that point they get squashed, rounded or cut off while the quieter parts carry on as before.

Bending a wave like this always makes new frequencies. They're harmonics, whole-number multiples of each note, and they're what you hear as grit, crunch, buzz or fuzz. How much you get, and which ones, depends on how far you push the sound and on the shape of the curve doing the pushing.

Engineers use the word for any change between input and output, including the gentle tilt an EQ puts on the frequency response, which some textbooks call linear distortion. Musicians mean the kind that adds frequencies that weren't there before. That's the subject of this page, and it covers the whole range from the slight thickening of saturation to a guitar that sounds like a chainsaw.

What does distortion do to a sound?

It changes several things at once, and it helps to listen for them separately.

The first is the harmonics. Soft curves add mostly low harmonics, the 3rd and 5th, which sit close to the note and thicken it. Sharp curves, like a hard clipper, add a long row that reaches far up the spectrum, which is why heavy distortion sounds bright and buzzy even on a dark sound. The harmonics screen in the lab measures this on a pure 110 Hz sine, so every bar after the first is something the curve added.

Then there's the level. A curve that squashes the peaks and leaves the rest alone shrinks the gap between the loudest and average level, the crest factor. A distorted guitar note holds its level as it dies away because, as the string gets quieter, the drive keeps pushing it into the curve, so the output stays near the ceiling for longer. Guitarists call that sustain, and it means distortion works a bit like a very fast compressor. In the lab, 12 dB of soft clipping takes the guitar loop's crest factor from 14 dB down to 6 dB.

The last change only happens when more than one note goes in at once. A curve doesn't know which part of the wave belongs to which note, so it also makes new frequencies at the sums and differences between them. That's intermodulation, and it's the reason distorted chords get messy so quickly. It has its own section below.

Reading the lab

The five cards along the top are the curves, and keys 1 to 5 switch between them while the lab has focus. Soft clip and hard clip are the two ends of ordinary distortion. Valve is a soft curve that leans to one side, the wavefolder flips peaks back down, and the bitcrusher rounds every sample to a coarse set of levels. The square screen draws the current curve, with dashed lines where the loop's loudest peaks land on it.

The harmonics screen is the one to watch on this page. Each bar is a harmonic of the test sine, odd ones in pink and even ones in amber, with its level in dB against the note written above it. The grey bar at the end is everything that isn't a harmonic, which for these curves is mostly aliasing. Next to it, the spectrum shows the real loop before and after, and while it plays you can watch new frequencies appear above each note.

Auto gain is on by default, so the lab keeps the distorted loop at the same loudness as the original and you can judge the sound without the volume fooling you. The panel on the right explains what your current settings are doing, with numbers measured from those screens. You can also upload your own file or record eight seconds from your microphone, and it stays on your device.

Types of distortion

Almost every distortion effect is a curve with a gain control in front of it, so the types differ mainly in the shape of the curve and in what's filtered before and after it. Ableton Live's Pedal device has three modes named after the main guitar pedal types: Overdrive, Distortion and Fuzz.

Overdrive

Overdrive is soft clipping. The curve bends gradually as the level rises, so quiet playing stays fairly clean and harder playing breaks up, which is why guitarists like it: it responds to how you play. The Ibanez Tube Screamer works this way: its clipping diodes sit in the feedback loop of an op-amp, which gives that gradual bend, and that stage gives the bass much less gain than the mids, so the low end distorts less and the result stays tight. In the lab, the soft clipper with 6 dB of drive puts the 3rd harmonic of the sine about 16 dB below the note; at 12 dB of drive it's 12 dB below.

Hard clipping

Turn the gain up, or use a sharper curve, and the peaks are cut flat. The ProCo RAT is a well-known example: its diodes clip the signal to ground after the op-amp, which gives a harder edge than the Tube Screamer's design. A flat top has sharp corners, and a sharp corner can only be built from a long row of high harmonics. With 24 dB of drive, the lab's hard clipper puts the odd harmonics at −10, −14, −17, −20 and −22 dB, close to the levels an ideal square wave has. The clipping lesson goes further into this end.

Fuzz

Fuzz is the most extreme of the three pedal types. Classic fuzz pedals use two or three transistors driven so hard that the wave comes out close to a square, often lopsided, with a raspy, sputtering decay. The pedal that made fuzz popular was the Maestro FZ-1 Fuzz-Tone, which Keith Richards used on the riff of the Rolling Stones' “(I Can't Get No) Satisfaction” in 1965, and a Fuzz Face was part of Jimi Hendrix's setup. The lab doesn't model a fuzz circuit, but a hard clipper with plenty of drive and the character turned up gets close to that lopsided square shape. Overdrive vs distortion vs fuzz compares all three.

Amp distortion

A guitar amp distorts in several places: the preamp valves, the power valves, the output transformer and finally the speaker, which can only move so far. Each stage adds its own curve, and a guitar speaker rolls off steeply above about 5 kHz, which is why a distorted amp sounds smoother than the same signal through a distortion plug-in with no speaker after it. Amp simulators copy that whole chain. The valve card in the lab is one lopsided valve stage, which leads with the 2nd harmonic at moderate drive; tube saturation covers it.

Wavefolding and bitcrushing

These two come from synthesisers and old samplers. A wavefolder flips the peaks back down instead of flattening them, so more drive puts more wiggles in every cycle. It gets extreme fast: at 9 dB of drive in the lab, the 3rd harmonic on the sine is 17 dB louder than the note itself and the 5th is about 7 dB louder. A bitcrusher forces the wave onto fewer levels, so instead of harmonics that follow the note it adds a grainy error that sounds like noise on quiet parts. Each bit you take away halves the number of levels. See wavefolding and bitcrushing.

Distortion types compared

The harmonic levels here are what the lab measures on its 110 Hz test sine, so you can check every one by setting it up yourself.

Why do distorted chords sound messy?

Put two notes through a curve together and you get the harmonics of each, plus intermodulation: new frequencies at sums and differences such as f2 − f1 and 2f1 − f2. Whether that sounds musical depends on the interval between the notes.

Take a power chord on A, which is just the root and the fifth: A at 110 Hz and E at about 164.8 Hz. The difference is 54.8 Hz, almost exactly the A an octave below. The sum is 274.8 Hz, very close to five times 55, and 2 × 110 − 164.8 is 55.2 Hz. Every new frequency lands near a multiple of 55 Hz, so the whole lot sounds like one rich A, and that's why rock guitarists play power chords through heavy distortion.

Swap the E for C♯, a major third up at about 138.6 Hz, and the difference is 28.6 Hz, with other products at 81.4 Hz, 248.6 Hz and 358.6 Hz. None of those is a multiple of 55, and because an equal-tempered major third is about 14 cents wider than the pure 5:4 ratio, they don't line up neatly with each other either. You hear that as a rough, beating mess, and with a full chord of four or five notes it gets worse.

Symmetrical curves, like the lab's soft and hard clippers with the character at zero, only make the odd-order products, the filled bars in the figure. Lopsided curves make the hollow ones too. The harmonics lesson has more on how this works.

Distortion depends on the level going in

A distortion plug-in reacts to how loud the signal is when it arrives. Drive is just gain in front of the curve, so a part peaking at −6 dBFS distorts more than the same part peaking at −18 dBFS with the same drive setting. If a distortion sounds different every time you change something earlier in the chain, that's usually why.

It also means the amount of distortion follows the dynamics of the performance. Loud notes break up and quiet ones stay cleaner, which is great on a guitar and less great on a bass line where you want every note to sound the same. A compressor before the distortion evens out the level going in, so the distortion stays the same from note to note.

Noise comes up with it. Anything quiet enough to stay under the bend, like amp hiss or the hum between notes, gets the full drive, while the peaks can't get any louder. With 24 dB of drive, the noise can end up as much as 24 dB closer to the notes than it was. A noise gate before the distortion stops it being pushed up in the first place.

Past a point, more drive stops adding harmonics. The lab's hard clipper at 24 dB already makes a near-square wave, and at 36 dB the harmonics on the sine barely move. Aliasing is what changes: it rises from −57 dB to −44 dB. The loop gets more squashed too, so if you want more edge by then, a brighter EQ after the distortion does more than another 10 dB of drive.

How to use distortion, step by step

1. Decide which part needs itDistortion works best on one or two parts that need to cut through or sound aggressive. On everything at once, it turns a mix into a wall of upper mids.
2. Filter what goes inPut an EQ before the distortion and cut the lows you don't want distorted. A high-pass at 80 to 150 Hz on a guitar, or 100 to 200 Hz on a copy of a bass, keeps the result tight.
3. Pick the curveSoft clipping for overdrive, hard clipping for buzz and aggression, a wavefolder for synth tones, a bitcrusher for lo-fi grit.
4. Push the drive past where you want it, then back offThe character is easier to hear when there's too much of it, so start there and bring it down until it sits right.
5. Shape the tone after itA low-pass or high shelf after the distortion tames fizz. Start around 5 to 8 kHz, which is roughly where a guitar speaker runs out.
6. Blend it if you need the original backA mix of 20 to 50% keeps the clean attack and low end, with the distorted copy underneath.
7. Match the level and compareSet the output so the distorted and bypassed versions are equally loud, then switch between them.

Where to use distortion in a mix

Bass and 808s

Distortion makes a bass audible on small speakers, because the harmonics it adds land in the range a phone or laptop can play, and your ear works out the pitch from them even when the lowest frequency is missing. The danger is the sub. With a lot of drive, clipping a long 40 Hz wave flattens it for most of its cycle, which turns a deep note into a fuzzy one and piles harmonics into the low mids. The safe way is to keep the original clean and distort a copy with the lows filtered out. Heavily distorted 808s are part of the sound of a lot of trap, and there the fuzz on the low end is the point, so let the genre decide.

Drums

On drums, a few decibels of clipping is hard to hear because the transients are so short, and it lets you make them louder at the same peak level. More obvious distortion works best in parallel, so the clean kit keeps its punch on top. A bitcrusher at 4 to 8 bits on a drum loop, mixed in at 30 to 50%, gives the grainy sound of old samplers. How to make drums hit harder covers clipping drums for loudness.

Vocals

Distortion on a lead vocal is usually an effect for one section, such as a bridge, a shouted line or an ad-lib. For a telephone or megaphone sound, band-pass the vocal to roughly 300 Hz to 3.4 kHz, the range old telephone lines carried, and put a hard clipper after it. Keep it on a separate track or a send so you can bring it in and out. Sibilant S sounds get harsh quickly through distortion, so a de-esser before it helps.

Synths and guitars

Synth leads and basses take heavy distortion well when they play one note at a time, because there's no intermodulation to worry about. Try the distortion before the synth's filter and then after it. On guitars, recorded distortion is normally part of the sound chosen at the amp, and adding more in the mix mostly adds noise and fizz. Play single notes or power chords into it, and save full chords for cleaner settings.

Starting settings for common sounds

These are starting points in the lab, where the drive is relative to a loop peaking near full scale. A real plug-in will need different numbers, but the order of things stays the same.

Unwanted distortion and how to avoid it

The distortion nobody wants is usually clipping at 0 dBFS. If you record too hot, the audio interface's converter runs out of numbers and cuts the peaks flat, and that can't be undone afterwards. Leave some headroom when you record: at 24-bit, peaks around −10 to −6 dBFS give you room for a loud take and lose nothing in quality.

Inside the DAW it's harder to clip by accident, because most DAWs mix in floating point and a channel can go over 0 dB without anything being cut. Some plug-ins do clip internally, though, and anything over 0 dBFS gets cut when you export to a fixed-point WAV. Gain staging covers keeping levels sensible through the whole chain.

If distortion appears only when you turn your monitors or headphones right up, it's coming from them. Small speakers run out of travel at high volume and distort on their own.

Common distortion mistakes

Distorting the sub-bass

The odd harmonics of a 40 Hz note land at 120, 200 and 280 Hz, right where the kick and the low mids already sit, so the low end turns woolly and the pitch of the sub gets harder to follow. Distort a filtered copy and leave the sub clean.

Distorting full chords

Big chords through heavy distortion produce intermodulation that's out of tune with the music. Distort single notes or fifths, or distort the chords lightly and get the aggression from another part.

Choosing it by volume

Distortion lifts the average level, so the distorted version wins every quick comparison. Switch Auto gain off in the lab and the panel tells you how much louder the loop got. Match levels before you decide.

Ignoring the fizz

A hard clipper adds harmonics all the way up the spectrum, and without a speaker or a filter after it they sound thin and harsh. Put a low-pass or a high shelf after the distortion and listen to how much smoother it gets.

Forgetting the noise

Drive brings up the hiss and hum between notes by the same amount it adds to the quiet parts of the music. Gate the signal before the distortion, or automate the distortion off in the gaps.

Training your ears to hear distortion

Heavy distortion is easy to spot; telling the curves apart is harder. The quiz under the lab plays the current sound through a soft clipper, a hard clipper or a wavefolder with the screens covered, at the same loudness as the original, and you name it. Listen to the edge of each note. The hard clipper puts a buzz on it that reaches right up the spectrum, the soft clipper's edge is smoother, and the wavefolder has a hollow ring the other two don't.

Questions people ask

Keep going