Flanger

Parameters

In the browser under MODULATION, beside the Chorus.

The Chorus with a return path — and that return is the whole device. One voice reads a short delay swept by an LFO, exactly as the Chorus does, but what the delay line recirculates is the input plus some of its own output. That feeds the comb filter back into itself: its gentle dips become resonant teeth, and sweeping them is the jet-plane sound.

Controls and display

Delay is much shorter than a chorus's. 0.5–5 ms is the flanger's range: the teeth then sit across the mids and above, where a sweep is audible as movement. Past about 10 ms they crowd into the low end and it stops sounding like a flanger.

Feedback's sign is two different devices. Positive resonates peaks at every multiple of 1/Delay, and the first notch sits between them at 1/(2·Delay). Negative puts the notches on the multiples themselves, so the first one lands an octave higher.

The one trap, and it sits on the defaults. Dry and wet mixed half-and-half with a negative feedback is very nearly an allpass filter — flat, and therefore inaudible. At Mix 0.5 with Feedback −0.62 the comb is 0.1 dB deep while every knob reads like it is working. With a negative setting take Mix up towards 1; with a positive one, 0.5–0.7 is deepest; and with no feedback at all, Mix 0.5 is the total cancellation people mean by "comb filter". The face tells you which of these you are in — see teeth, below.

What to reach for it for. A flat DI guitar or synth that needs movement rather than width, a drum loop that wants a hook on its last bar, an effect return that should be the interesting thing. It is not a widener (that is the Chorus, or Band Width) and it is not a tone control: a comb removes energy at every notch, so on a full mix or a bus it reads as phasiness. Keep it on a stem.

Surface (the comb): the big card is the device's own frequency response, drawn live from the same delay the audio engine is reading at this instant — solid for the left channel, dashed for the right, set apart by the Width angle. Two faint curves behind them are the response at the two ends of the sweep, so the band between them is where the teeth travel even in a still picture. The lowest notch is stamped where it sits, found on the curve itself rather than from a formula, so the label can never disagree with what you can see.

Drag sideways on the picture to move the comb in frequency (Delay), up and down to open the travel (Depth); double-click to snap the rate to the nearest note value at the session tempo. Rate, Depth, Delay, Mix and Width sit in a deck under it.

The middle card is the Feedback dial, with zero at the top and the polarity spelled out underneath — peaks on 1/delay or notches on 1/delay, and FLAT — RAISE MIX in amber when the setting has cancelled the comb. The right card leads with teeth: how deep the comb is, loudest point minus quietest. It is the answer to "is this doing anything" — under about 3 dB it is not, whatever the other knobs read. Under it: notch 1, spacing (1/Delay — how far apart the teeth are), period, wet (the line output's level, the only measurement on the face) and the session tempo.

With the device off or nothing playing, the comb stands still and wet reads a dash.

The agent may use the flanger, with Mix capped at 0.5 and Feedback at ±0.7 — it can add movement, not park a comb on the edge of self-oscillation. Your own knobs go all the way.