What is a flanger?

The short answer

A flanger takes your sound, makes a copy, delays that copy by a very short amount (roughly one to ten thousandths of a second), and mixes it back in with the original. Summing a sound with a slightly delayed version of itself cancels some frequencies and boosts others, carving a row of evenly spaced dips out of the tone. That shape is called a comb filter, because a chart of it looks like the teeth of a comb.

On its own, a fixed comb is just a static coloration. What makes a flanger a flanger is that the delay is never held still: a slow control wave nudges it longer and shorter, over and over, so the whole row of dips glides up and down through the sound. That gliding sweep is the instantly recognizable whoosh, the sound of a jet passing overhead. The name is a studio relic: engineers used to press a finger on the flange, the raised rim, of a tape reel to drag one copy slightly behind another and get exactly this effect.

Summing a delayed copy makes a comb

To see where the dips come from, picture a single steady tone and its delayed copy landing on top of it. If the copy arrives lined up with the original, the two add together and that frequency gets louder. If the copy arrives half a cycle late, its peaks land on the original's troughs and the two cancel, so that frequency nearly disappears. This is ordinary interference, the same adding and cancelling any pair of copies does.

The catch is that a single fixed delay lines up differently for every pitch. A low tone with a long wavelength might arrive perfectly in step, adding to itself, while a higher tone, whose shorter wavelength lets that same fixed delay land it half a cycle late, falls out of step and cancels. Work through the whole range and you get cancellation at one frequency, then reinforcement, then cancellation again, at regular intervals all the way up. The result is a series of notches spaced evenly across the spectrum, which is why a flanger is really a filter you build out of a delay rather than out of tone controls.

The spacing is set entirely by the delay time, and it is the tidy, harmonic part of the flanger's character.

Because every notch sits one fixed step above the one below it, they are evenly spaced across the whole spectrum. That even, harmonic layout is exactly what your ear reads as a metallic, resonant color, and it is the single biggest thing that separates a flanger from its cousin the phaser, which we will get to below.

Sweep the delay and the comb moves

Hold that comb still and you have a fixed, slightly hollow tone. The magic is in moving it. A flanger runs a low-frequency oscillator, a slow control wave well below hearing, that gently rocks the delay time longer and shorter a few times a second. As the delay changes, the notch spacing changes with it, so every notch slides at once and the entire comb sweeps up and down the spectrum. Sweeping a whole bank of harmonic notches across a sound is the jet-plane whoosh.

Two controls shape the movement. One sets how fast the comb sweeps, the speed of that control wave, from a slow ocean swell to a fast warble. The other sets how far it travels, how much the delay stretches on each pass, which is the difference between a subtle shimmer and a dramatic full-range sweep.

Feedback sharpens the whoosh

A plain comb has fairly soft, shallow notches. To make the effect more intense, a flanger usually feeds a little of its output back into its own input. Each pass through the short delay reinforces the pattern, which deepens the notches and raises sharp resonant peaks between them. Turn feedback up and the whoosh goes from a gentle sweep to an aggressive, ringing, almost metallic tear.

Feedback is the control that pushes a flanger toward its most obvious, showy sound. A touch adds body and motion; a lot turns your voice into something that sounds like it is being pulled through a pipe. Like most modulation, it flatters the sound in small doses and becomes an effect you reach for on purpose in large ones.

Flanger, chorus, and phaser

Flanging belongs to a family of modulation effects that all move a copy of your sound with a slow control wave, so it is easy to mix them up. The differences come down to how long the delay is and how the notches are made.

• Chorus uses a longer delay, around ten to thirty milliseconds, and leans on the slow detuning of that delayed copy rather than on a strong comb. Instead of a sweeping whoosh you hear an ensemble: several slightly-out-of-tune voices at once, a thickening rather than a filter. See what is chorus for the full picture.
• Phaser also carves moving notches, but it makes them a completely different way, with a chain of phase-shifting stages rather than a delay. The result is fewer notches, and crucially they are not evenly spaced, so the sweep sounds smoother and more liquid than the flanger's hard, harmonic, metallic comb. See what is a phaser for how those stages work.

A useful shortcut: chorus thickens, phaser swirls, and a flanger whooshes. If you can hear a row of resonant, evenly spaced notches sweeping through the sound, you are hearing a flanger.

The flanger in patchd

In patchd, the Flanger is one node in the Studio voice-fx rack, sitting in the same picker as reverb, delay, and the other effects. You add it to a channel like any other DSP node and drop it into the order you want. It gives you five controls, and each maps straight onto the ideas above:

• Rate sets how fast the comb sweeps, the speed of the control wave inside the node.
• Depth sets how far it sweeps, how much the delay stretches on each pass.
• Feedback deepens the notches and sharpens the peaks, taking the whoosh from gentle to metallic.
• Manual sets the base delay, where the comb sits before the sweep moves it, so you can park it high and bright or low and hollow.
• Mix blends the flanged copy against the untouched signal, from a hint of movement to a full, drenched sweep.

There is no separate, routable oscillator to wire up: the control wave lives inside the node, and Rate and Depth are simply its speed and its amount. The short delay the flanger uses to build its comb is part of the sound itself, not something between you and your own voice. Because the engine is real time and runs over the low-overhead Windows audio paths, its internal latency stays in the single-digit milliseconds at a small ASIO buffer, and adding a Flanger does not change that, so you can hear the sweep on yourself live while you dial it in.

The takeaway

A flanger mixes your sound with a very short delayed copy, which builds a comb filter: a row of evenly spaced, harmonically related notches across the spectrum. A slow control wave sweeps that comb up and down, and feedback sharpens it, which together make the sweeping jet-plane whoosh. It is close kin to chorus, which thickens with a longer delay, and to the phaser, which swirls with fewer, unevenly spaced notches. Once you can picture the moving comb, the whole family clicks into place.

patchd is a pre-launch Windows audio mixer with a full effects rack on every channel and a Studio voice-fx rack that includes the Flanger among its modulation nodes. If you want a mixer that can add real movement to your voice in real time, join the waitlist and get notified when it ships. There are two tiers, Free and Studio; the Studio tier is $39.99 per year, and the real-time engine is identical on both.