What is a flanger?

Flanging in plain English

Take a sound, make a copy, and play the copy a couple of milliseconds behind the original. That gap is far too short to hear as an echo, so the two blend into one sound, but they no longer line up perfectly. Some frequencies arrive in step and add together. Others arrive exactly out of step and cancel, which leaves narrow gaps in the spectrum called notches.

Now let a slow oscillator, an LFO, move the delay up and down. Every notch moves with it: when the delay gets longer they slide down towards the bass, and when it gets shorter they rise again. That rising and falling is the sweep you hear as flanging.

Most flangers add one more ingredient, feedback, which sends the delayed copy back into the delay. It sharpens the sweep into the ringing, metallic sound most people picture when they hear the word.

Where the name flanger comes from

Flanging started on tape. Engineers played the same recording on two tape machines at once, mixed their outputs together and slowed one of them by pressing a finger against the flange, the rim of its tape reel. As that machine fell a few milliseconds behind and then caught up, the comb swept through the music. Small Faces' “Itchycoo Park” from 1967 is one of the best-known records made this way.

Tape could do one thing a lot of flanger plug-ins can't. Either machine could be the one running late, so the delay between them could shrink to nothing and come out the other side. At the exact moment the two copies lined up, every notch shot off above the top of hearing and the sound came back whole for an instant. That's called through-zero flanging. A digital flanger can't play a sound before it arrives, so to do the same it has to delay the original as well, and plug-ins that bother usually call it a through-zero mode. The lab's flanger never goes below 0.5 ms, so it doesn't do this.

Reading the lab

The lab opens on a drum loop, because hi-hats and cymbals have energy right up the spectrum for the notches to cut into. The Chorus and Phaser cards are there for comparison, and each card keeps its own settings.

The wide screen at the top shows the whole loop, with time running left to right and frequency up the side. Wherever the flanger cancels a frequency the colour goes dark, so a flanger draws a set of dark bands that rise and fall together as the delay moves. Hover over it, or press and drag on a phone, to read the delay and the notch frequencies at any moment.

Underneath on the left is the LFO, drawn as the delay time in milliseconds, with a dot at the moment you're hearing. The middle screen is the spectrum right now. Its faint line is the original and the coloured shape is the flanged sound, while the white line is the shape of the comb at that instant, with each notch marked along the bottom. The panel on the right describes your settings using numbers measured from the loop, such as the delay range and the lowest notch.

Every card plays at the same loudness as the original, so feedback can't win you over just by making things louder. You can swap the loop for your own sound by uploading a file or recording eight seconds, and it never leaves your device.

How does a flanger work?

The comb filter

A frequency cancels when the delay is exactly half of one of its cycles, because the copy then reaches the bottom of the wave just as the original reaches the top. The same happens at one and a half cycles, two and a half, and every odd number of halves after that. So a delay of d seconds cuts its first notch at 1 ÷ (2 × d), and the rest follow at regular gaps of 1 ÷ d.

With a 1 ms delay, that puts the first notch at 500 Hz and the others at 1.5 kHz, 2.5 kHz, 3.5 kHz and on up, 1 kHz apart. At 2 ms every figure halves: 250 Hz, 750 Hz, 1.25 kHz, 500 Hz apart. Drawn on a spectrum the pattern looks like the teeth of a comb, which is where the name comb filter comes from. The comb filtering lesson covers the same effect when it happens by accident, between two microphones or two copies of a track.

Halfway between two notches, the copy arrives a whole number of cycles late and adds to the original. With the mix at 50% those frequencies come out at their original level, while the notches go all the way down to silence.

The sweep

A still comb sounds hollow, a bit like talking through a cardboard tube, and your ears soon stop noticing it. A flanger keeps it moving. The LFO swings the delay between a shortest and a longest value, and because every notch is set by the delay, the comb moves as one: longer delays pack the notches closer together and pull them down, and shorter ones spread them out and push them up.

In the lab, a depth of 70% sweeps the delay from 0.5 ms to 7.15 ms. At the short end the first notch is at 1 kHz. At the long end it's down at 70 Hz, with more than 140 notches below 20 kHz. Your ear follows the movement as a pitch gliding down and back up, even though the flanger never changes the pitch of anything in the sound.

Feedback and the jet sound

Feedback takes some of the delayed copy and sends it round the delay again, so each frequency gets a second, third and fourth chance to line up. The ones that line up every time, at whole multiples of 1 ÷ delay, build into sharp peaks. Those peaks have the same spacing as the harmonics of a note, so you hear a ringing tone with a pitch of 1 ÷ delay. At 1 ms that's around 1 kHz; at 5 ms it's 200 Hz.

This is why a flanger with plenty of feedback sounds pitched and metallic. At the lab's 70% depth the tone glides from 2 kHz down to 140 Hz and back, almost four octaves, every time the LFO goes round. Seventy per cent feedback at a 50% mix puts about 15 dB between the peaks and the notches, where with the feedback off there are no peaks at all.

Some flangers let the feedback go below zero. Negative feedback flips the polarity of the copy each time it goes round, which moves the peaks to the places the notches used to be, at odd multiples of half of 1 ÷ delay. The tone drops an octave and sounds hollower, because only the odd harmonics are left, as in a square wave. The lab's feedback only goes positive, so try this one on your own flanger.

The controls

Flangers name their knobs differently, so it helps to know the job behind each label. The MXR M117R pedal calls its four Manual, Width, Speed and Regen, and plug-ins such as Logic's Flanger, Ableton Live's Phaser-Flanger and FL Studio's Fruity Flanger use their own names again. Underneath, they all set the same handful of things.

Delay, or manual

The delay knob, called manual on many pedals, sets the delay the sweep is built around, and so where the comb sits. Turn it up and the whole sweep moves lower, which sounds darker and more hollow. With the LFO depth at zero it's the only thing setting the comb, and the flanger turns into a still comb filter. In the lab the shortest delay is fixed at 0.5 ms and the depth decides how far up from there it goes.

Depth

Depth, sometimes labelled width, sets how far the LFO moves the delay. In the lab the longest delay is 0.5 ms plus 9.5 ms times the depth, so 50% reaches 5.25 ms and 100% reaches 10 ms, which takes the first notch from 1 kHz all the way down to 50 Hz. Low depths keep the sweep in the top end, where it reads as a shimmer on the hats. High depths drag the comb through the low mids and the bass, and that's where it's most obvious.

Rate

Rate is the speed of the LFO in hertz. Flangers are usually set slow, between about 0.1 and 0.5 Hz, so each sweep takes a few seconds and you can follow it. Past 2 Hz or so the sweep turns into a wobble, and the fast-moving delay starts to bend the pitch the way a chorus does.

Matching the rate to the tempo keeps the sweep in step with the song. At 120 BPM a bar lasts two seconds, so 0.5 Hz is one sweep a bar, 0.25 Hz is one every two bars and 0.125 Hz is one every four. The lab rounds the rate to a whole number of cycles per loop, which on the 8 second drum loop means steps of 0.125 Hz. Many plug-ins can set the rate in bars or note values, and some offer a triangle LFO next to the sine; a triangle sweeps at a constant speed and turns round sharply at each end.

Feedback

Feedback, also called regeneration, regen or resonance, decides how metallic the flanger sounds. Around 20 to 40% adds an edge. From 60 to 80% you get the full jet, and close to 100% the peaks ring on after the sound has stopped and can come out several decibels louder than the original. The lab stops at 90%, where the peaks are already more than 8 dB up.

Mix

Mix balances the original against the delayed copy, and the comb only exists while both are there. At 50% the notches are as deep as they get. Pull the mix down to 30% with a little feedback and they only cut about 7 dB, which is often all a part needs inside a busy mix. At 100% there's nothing left for the copy to cancel against, so with the feedback off the notches disappear and all that remains is a faint pitch wobble from the moving delay.

On a send, set the flanger itself to 100% wet and use the send level as the mix, since the dry sound is already on the channel.

Stereo and spread

A stereo flanger runs a separate LFO for each side and sets them out of step. In the lab, Spread moves them up to half a cycle apart, so at 100% the comb on the left is at its lowest while the one on the right is at its highest, and on headphones the sweep seems to move around your head. Check it in mono before you commit. When the two sides are added together, each side's comb partly fills in the other's notches, so on a phone speaker the sweep can come out weaker and lumpier than it sounded on headphones. The mono compatibility lesson shows what to listen for.

Flanger vs chorus and phaser

A chorus is built the same way as a flanger, with longer delays of about 10 to 30 ms and often more than one copy. At those lengths the notches crowd together and move too much to follow, so the sound just gets thicker. A phaser makes its notches with allpass filters in place of a delay, and gets only a few wide ones that aren't evenly spaced. So its sweep is softer, and with feedback it never builds the evenly spaced row of ringing peaks that gives a flanger a pitch of its own. Click the Chorus and Phaser cards in the lab to hear them on the same loop, or read chorus vs flanger vs phaser for all three side by side.

How to set up a flanger

1. Use a send if the part has bass in itFlanging a kick or a bassline sweeps notches through the low end, so the bottom of the mix comes and goes. On a send you can high-pass the return at around 150 to 200 Hz and keep the low end where it was.
2. Start with a 50% mix and no feedbackThe notches are at their deepest, so you can hear exactly where the comb is while you set the rest.
3. Set a slow rate in time with the songOne sweep every one, two or four bars. At 120 BPM that's 0.5, 0.25 or 0.125 Hz.
4. Bring the depth upStop when the sweep reaches as low as you want it. Further down means more drama and more movement in the low mids.
5. Add feedbackRaise it until the sweep rings the way you want, then back it off a little, because feedback adds level at the peaks.
6. Set the mix in contextBring it down until the flanger sits in the track, then check the whole mix in mono.

Using a flanger on drums, guitars, synths and vocals

Drums

Drums show a flanger off better than almost anything. Hats, cymbals and snare rattle are close to noise, so the comb has something to cut at every frequency it passes through. Flanging a drum break or a hat loop for the last bar or two before a drop, then pulling it out, is a common way to build a transition in dance music. Pick Pink noise in the lab to hear the comb with nothing else in the way.

Guitars

On an electric guitar the flanger usually goes after the distortion. A distorted guitar is full of harmonics, so the sweep stands out. Put the flanger first and the distortion fills the notches back in with new harmonics, which gives a subtler, grittier sweep. Clean guitar takes a flanger with low feedback and modest depth as a slow shimmer; choose the Guitar loop in the lab to try it. The effect order lesson covers where else it can sit in a chain.

Synths and pads

Pads and chords suit a slow flanger with the feedback kept low. On a bright, saw-heavy synth, high feedback gives a sweep that sounds a lot like a resonant filter being swept, and a flanger on a riser or a noise sweep adds movement to a build.

Vocals

Keep it to a word or a phrase. A flanger across a whole lead vocal gets tiring quickly and makes the voice sound processed, so automate the send up for the moment you want and back down after it. Backing vocals and ad-libs can take more.

Starting settings for a flanger

The depth figures are for the lab, where 100% means a 10 ms longest delay. On other flangers, read them as low, medium or high.

Common flanger mistakes

Flanging the low end

At a 7 ms delay the first notch sits at 70 Hz, close to where a kick's weight lives, so as the comb sweeps, the bottom of the mix gets thinner and fuller every few seconds. High-pass the flanger's return, or keep the depth low on anything with weight in it.

Running the mix at 100% on an insert

With none of the original left there's nothing to cancel, and a flanger with low feedback seems to do almost nothing. If yours sounds like a faint wobble, check the mix before you reach for more depth.

Feedback that rings in the wrong key

With high feedback and a small depth, the flanger rings at nearly one pitch, and on a sustained part that tone can clash with the song. Back the feedback off, or set the delay so it rings on a note that fits. A delay of 9.09 ms rings at 110 Hz, which is an A, and 4.55 ms rings at 220 Hz, the A an octave up.

A sweep that ignores the tempo

A rate picked by ear lands at a different point in every bar, so a looped part sounds unsettled from one bar to the next. Set it to a whole number of bars per sweep, or use the plug-in's tempo sync.

Training your ears to hear a flanger

The quiz under the lab plays the current sound through a flanger, a chorus or a phaser with random settings. It covers the screens and the controls and matches the loudness, and you say which one it was. The phaser is the easiest one to mistake for a flanger, so listen for the ringing, pitched edge that only a flanger's evenly spaced comb makes. Eight rounds take a few minutes, and your best score is kept in your browser.

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