A phaser passes a sound through a chain of all-pass filters that shift the phase of some frequencies, then mixes that phase-shifted copy back with the dry sound. Where the two are out of step they cancel, which carves a set of dips, or notches, into the tone, and sweeping the filters with a slow oscillator slides those notches up and down. The result is a soft, swirling, watery sweep.
The controls are much the same on almost every phaser, hardware or plugin: a rate, a depth, a number of stages, a feedback or resonance, and a mix. None of this is tied to one product.
A phaser is a modulation effect that passes a sound through a chain of all-pass filters, which shift the phase of different frequencies by different amounts, and then mixes that shifted copy back in with the original. Where a frequency in the copy ends up out of step with the same frequency in the original, the two partly cancel and leave a dip, or notch, in the tone. A slow oscillator moves those notches up and down the frequency range, and that moving pattern of notches is the swirling, watery sweep a phaser is known for.
The sound is often described as swirling, hollow or underwater, a gentle whoosh that seems to turn a sound inside out as it passes. Used lightly it adds a subtle sense of motion and a little shimmer; pushed harder, with plenty of feedback, it becomes a strong, resonant, almost vocal sweep that is a clear character in its own right. Because a phaser builds its notches from filters rather than from a delay, they sit at uneven spacings, and that tends to make it sound smoother and more liquid than the more metallic sweep of a flanger.
A phaser does not add new notes or harmony. It is still one part, played once, with a filtered copy of itself mixed in beside it. Everything it is known for, the swirl, the hollow sweep and the sense of motion, comes from that copy having its phase shifted by a bank of filters so the two versions cancel at moving points across the tone. Turn the effect off and the sweep vanishes, because there was only ever the one sound.
A phaser works by splitting the signal in two, sending one path through a series of all-pass filter stages, and mixing it back with the dry path while a low-frequency oscillator, or LFO, sweeps the filters. An all-pass filter is the key part: it passes every frequency through at the same level, so on its own it changes no volume and no tone, but it delays the phase, or timing, of different frequencies by different amounts. Stack several of these stages in a row and the phase shift builds up, so by the time the signal reaches the output some frequencies are well out of step with the dry copy.
When you add that phase-shifted path back to the dry path, the frequencies that end up roughly opposite in phase cancel each other and leave notches in the tone, while others reinforce. Sweeping the filters with the LFO moves the point where each cancellation happens, so the whole set of notches slides up and down, and that motion is the sweep you hear. The notches are not evenly spaced, because the phase shift from a bank of all-pass filters does not line up in the neat, regular way that a short delay does. If the idea of two versions of a sound cancelling is new, our guide on phase in audio covers the basics.
The two controls you reach for first are rate and depth. Rate, sometimes called speed, sets how fast the LFO sweeps the filters, from a slow drift that takes several seconds to a fast, dizzy wobble. Depth sets how far the sweep travels, which is how far the notches move across the tone, so more depth is a wider, more obvious effect. A stages or poles control, where a unit offers one, sets how many all-pass filters are in the chain, and roughly speaking every two stages adds another notch, so more stages means more notches and a thicker, more intense sweep.
Two more controls decide how strong it is. Feedback, sometimes labelled resonance or regeneration, sends some of the filtered path back through the filters again, which sharpens the notches and makes them ring; it intensifies the effect and, pushed far, gives that resonant, almost speaking quality. A mix or blend then sets the balance of dry sound to the phased copy, and keeping some dry keeps the part clear and the swirl sitting under it rather than swallowing it.
The main difference is how the notches are made and how they are spaced. A phaser builds its notches with a bank of all-pass filters, so the notches sit at uneven, non-harmonic spacings, and that makes the sweep sound smooth, hollow and watery. A flanger makes its notches a different way, with a very short delay, roughly 1 to 10 ms, which stacks the copy against the original as a comb filter of evenly spaced notches, so its sweep sounds more metallic and jet-like. Both use an LFO to move the notches, and both can be fed back to ring, but the shape of the notches is what sets the two sounds apart.
| Effect | How it works | What you hear |
|---|---|---|
| Phaser | A bank of all-pass filters shifts the phase of the signal, swept by an LFO and often fed back, so the notches it makes are not evenly spaced. | A soft, swirling, watery sweep that is smooth and hollow, more resonant and vocal when the feedback is high. |
| Flanger | A very short delay, roughly 1 to 10 ms, swept by an LFO and often fed back, making evenly spaced comb-filter notches that move. | A strong, whooshing sweep, the classic jet-plane sound, metallic and ringing when the feedback is high. |
In practice a phaser is the smoother, more liquid of the two, and a flanger the more aggressive and metallic, because a flanger's notches are stacked in a regular comb while a phaser's are spread unevenly. Our guide on the flanger effect covers that one in full. A third close cousin, the chorus effect, uses a longer delay to thicken and widen a sound rather than to sweep it, so it adds body without the hollow whoosh. Many units offer more than one of the three, since they are built from the same idea of mixing a moving copy back with the original.
A phaser is good for adding a gentle, swirling movement to sounds that would otherwise sit still: electric guitars, electric piano, pads and synths, and anything that holds a note long enough to hear the sweep pass through it. It is a motion and character effect, so it earns its place where you want a sense of movement and a soft shimmer rather than a change to the notes.
A phaser is smoother than a flanger, but it is still an obvious effect once the depth and feedback are up, and a fast, deep phase running through a whole song can quickly feel busy or seasick. Many people keep it slow and shallow so it reads as gentle motion, or automate a stronger setting in for a moment, a build or a single section, then take it back out. When you want it as a steady texture, back the depth and feedback off until it sits under the part rather than swirling over the top of it.
A phaser is a finishing touch. It adds movement and a swirling character to a sound, but it cannot invent the sound in the first place, and a flat, static part with a phaser swept across it is still a flat, static part underneath. The interesting work is making a source that already moves, so the phaser becomes a flourish you add by choice rather than a way to fake life that is not there.
We do not make a phaser plugin, and this guide is not a pitch for one. But a phaser is easiest to use well when the sound going into it already moves and evolves on its own, so you sweep it in as a flourish rather than to inject life into a static part. That is what our instruments are built to do. The Collection is our three instruments together, ARGISH, SILT and REHEAT, with three separate licence keys. Each one already carries its own motion: ARGISH is a self-playing drone synth, SILT is a tape-loop instrument that wears sounds into texture, and REHEAT writes acid lines. Parts like that arrive with movement of their own, so a phaser becomes a choice rather than a rescue.
Every one ships as AU, VST3, AAX and a standalone app on macOS, signed and notarized, and a VST3 on Windows. You can hear one free in your browser first, no install and no account, then decide.
Everything on this page works by hand with any phaser in any DAW, which is rather the point of writing it down.
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