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Modulation Effects Explained: Chorus, Flanger, Phaser
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From the music-learning collection, adapted for Philojain Music Muse. Referenced sources remain credited in the article.
Chorus, flanger and phaser all start from the same basic idea — a modulated copy of your signal mixed back with the original — and it’s exactly that shared root that makes them easy to confuse. Tremolo works differently, modulating volume rather than the signal itself, but gets lumped into the same ‘modulation’ family by habit.
This guide starts from the shared mechanism, then shows exactly where each effect diverges from it, so the difference stops being ‘chorus sounds shimmery, flanger sounds swooshy’ and starts being something you can actually predict.
The Shared Mechanism: A Modulated Short Delay
Chorus, flanger and, in a different way, phaser all begin with a short delay whose time is constantly, slightly varied — modulated — by a low-frequency oscillator, then blended back with the dry signal. That constant tiny pitch and timing wobble against the steady original is what creates the moving, animated character common to all three.
- Delay time is the main thing separating chorus from flanger — longer, more varied delay times read as chorus; very short delay times read as flanger.
- Phaser doesn’t use a delay line at all — it uses shifting all-pass filter stages instead, but the audible effect lands in the same family by ear.
Chorus: Width and Thickening
Chorus uses a longer modulated delay time than flanger, which reads less as an obvious sweeping effect and more as width and thickening — like doubling the part slightly out of tune and out of time with itself, the way a chorus of voices naturally doesn’t lock perfectly together.
- Use chorus to thicken a single guitar into something closer to two guitars playing together, especially on clean or lightly driven tones.
- Heavier chorus settings — deeper, slower modulation — push toward a more obviously wobbly, vintage character rather than subtle width.
Flanger: The Sweeping, Jet-Plane Sound
Flanger uses a much shorter modulated delay time than chorus, which creates comb filtering — peaks and notches in the frequency response that sweep up and down as the delay time changes. That sweeping comb filter is the source of flanger’s signature ‘jet plane’ sound, a much more obvious and aggressive effect than chorus.
- A feedback or ‘resonance’ control on a flanger emphasizes the comb-filter peaks further, making the sweep more pronounced and metallic.
- Flanger is far more noticeable at higher gain, where the comb filtering interacts with a saturated signal’s harmonics more dramatically than it does on a clean tone.
Phaser: Sweeping Without the Delay Line
Phaser creates its moving character with all-pass filter stages that shift phase rather than delay time, producing notches in the frequency response similar in spirit to flanger’s comb filtering, but generally fewer, wider and smoother-sounding — phaser tends to read as a gentler, more musical sweep than flanger’s harder jet-plane effect.
More filter stages — ‘4-stage’, ‘6-stage’ and so on — generally means more notches and a more complex, layered sweep; fewer stages gives a simpler, more subtle pulse.
Tremolo: The Odd One Out
Tremolo doesn’t modulate delay time or phase at all — it modulates volume, rhythmically raising and lowering the signal’s level. It’s grouped with modulation effects by convention, and because it shares the same low-frequency-oscillator building block, not because it works the same way as chorus, flanger or phaser.
For where any of these belong in your signal chain, the pedalboard-order guide on this site covers placement in full — the short version is that modulation effects usually sit after gain-based pedals and before or in an amp’s effects loop, depending on how processed you want them to sound.
Frequently asked questions
What’s the actual difference between chorus and flanger?
Delay time. Chorus uses a longer, more varied modulated delay that reads as width and thickening; flanger uses a much shorter delay that creates a sweeping comb-filter sound.
Is phaser just a subtler flanger?
Not mechanically — phaser uses phase-shifting filter stages instead of a delay line — but the audible result is often a gentler, smoother sweep compared to flanger’s harder jet-plane effect, which is a fair way to describe the difference by ear.
Why is tremolo considered a modulation effect if it doesn’t sweep like the others?
It shares the same low-frequency-oscillator building block as chorus, flanger and phaser, just applied to volume instead of delay time or phase — the family grouping is about the underlying mechanism, not the audible result.
Where should modulation effects go in my signal chain?
Generally after gain-based pedals, either before the amp or in an effects loop — see the pedalboard order guide on this site for the full placement logic.
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Modulation, mechanism by mechanism
Modulation (13)
All-pass stage
Equal gain at every frequency with phase shifting continuously from 0° toward 180°, passing exactly 90° at the stage's own corner frequency.
nothing on its own — audible only once it is mixed back against the dry signal
Stages to notches
n all-pass stages produce n/2 notches. A Phase 90's four stages give two notches, with calculated rest positions at 58.5 Hz and 340.8 Hz; a Phase 45's two stages give one.
fewer stages sounding gentle and watery, more stages sounding thick and jet-like
Phaser modulator type
A Phase 90 sweeps four matched JFETs used as voltage-controlled resistors; a Small Stone modulates OTA transconductance directly.
the same effect with a different sweep character — one liquid and even, the other harder-edged
Uni-Vibe stagger
Four phase stages with deliberately mismatched capacitors — 330 pF, 470 pF, 4 nF and 15 nF — all swept by one incandescent bulb driving four photocells, which respond faster to rising light than to falling.
an uneven, lopsided throb with unequally spaced notches, quite unlike an evenly matched phaser
Chorus
A modulated delay of roughly 5–40 ms with no feedback path. The sweeping delay length Doppler-shifts the wet copy, which is the detuning.
two slightly out-of-tune guitars playing the same part
Flanger
A modulated delay under about 20 ms with feedback, producing evenly spaced comb notches that regeneration deepens and narrows.
a metallic jet sweep rather than a detuning — hollow and watery on negative feedback, whooshing on positive
Vibrato
Pitch modulation with no dry signal mixed in, so there is no comb filtering at all.
pure pitch wobble, with none of the hollowness of chorus or phase
Optical tremolo
An LFO drives a lamp — a neon needs about 90 V to strike — sensed by a photocell forming part of a divider. The lamp re-striking each cycle is what makes it choppy.
a hard, square, stuttering throb rather than a smooth swell
Bias tremolo
The LFO is ridden onto the power tubes' grid bias, cyclically shifting the output stage's operating point and therefore its gain.
a thicker, gooier pulse that changes the amp's distortion as well as its level
Harmonic tremolo (brownface)
The signal is split by an RC crossover — about 320 Hz on the Fender 6G4 — into two bands whose gains are modulated out of phase with each other, then recombined. As treble rises, bass falls.
a swirling, phase-like sway rather than a simple volume pulse
Rotating baffle (Leslie / Vibratone)
A real speaker mechanically Doppler-shifted by a spinning baffle or horn.
a three-dimensional wobble with genuine pitch and amplitude movement that no phase-shift circuit reproduces
Whammy flutter
The tremolo arm held constantly so sustained notes never sit still in pitch.
every long note drifting and wobbling slightly, never settling
Glide guitar
The vibrato arm held through strummed chords so the entire chord's pitch bends continuously.
whole chords sliding and warping in pitch as they ring
About this reference
From the music-learning collection, adapted for Philojain Music Muse. Referenced sources remain credited in the article.
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