The Phaser

All-pass stages move notches for a sweep that is softer and wider than flanging.

Related

PhaseModulationPolyphonic synthesis

The question

A phaser also sweeps, but it does not use a delay. It shifts phase with all-pass filters instead. The result is softer than flanging, and its notches are not spaced in a harmonic series.

How it works

Several all-pass stages shift phase around a set of frequencies. Summing that path with the dry signal creates notches. An LFO sweeps the centre frequency, so the notches move. More stages mean more notches; feedback deepens them and adds resonant peaks. Because the spacing is uneven, a phaser lacks the metallic comb of a flanger.

Settings and what you hear

Four stages are the gentlest setting, while 8 to 12 are more obvious. A rate of 0.05 to 1 Hz suits pads, and above 2 Hz suits rhythmic material. Depth sets the sweep range, and feedback around 20 to 50 percent adds bite. An equal blend makes the notches clearest; fully wet becomes a different tone altogether.

What to listen for

On an ambient pad, set the rate to 0.1 Hz and hear the notch travel from low to high like moving mist. On a jazz-funk loop, notice whether the hi-hat seems to drift as the sweep passes. Unlike a flanger, it moves wider and slower.

Common misconceptions

That a phaser changes stereo position; that more stages are always better; that a phaser and a flanger are the same effect.

Sources

• Vadim Zavalishin, The Art of VA Filter Design — all-pass stages checked, not quoted
• Udo Zölzer, DAFX — Digital Audio Effects, modulation chapter — background checked, not quoted

Used for fact-checking only; all prose is original.