Phaser

A phaser is a tone-based modulation effect, and, like its cousins the chorus and the flanger, it can be used both while composing a song or added later during the mixing stage. You’ll find many guitar pedals and amplifiers that include the effect.

Although it sounds a lot like a chorus or a flanger, a phaser works by a slightly different mechanism.

The reason a phaser sounds similar to those other effects is that it also copies the signal of the track on which it is placed and alters that copy. What makes it different is the way in which it alters the copy, which is through the application and modulation of something called an “all-pass filter.” An all-pass filter, which can also be found in many EQ plug-ins, flips the phase of a piece of audio at a particular point on the frequency spectrum. Now, on its own, this has no noticeable effect on the sound of that audio, but when blended with the original audio, the difference becomes obvious. “Phase” refers to the position of the peaks and valleys that comprise a particular waveform. If that waveform is flipped vertically, its peaks become valleys, and its valleys become peaks. When two identical waveforms overlap, such that the peaks and valleys point in the same direction, the audio increases in volume. However, when the peaks and valleys point in opposite directions, “destructive interference” is created, and the audio will sound much thinner. By flipping the phase of a copied piece of audio at a particular place on the frequency spectrum using an all-pass filter and then blending it with the original audio, a phaser introduces this thinning effect to the sound of a track. It then modulates the frequency of the all-pass filter, which sweeps it up and down the frequency spectrum. Many phasers will use multiple all-pass filters spread out across the frequency spectrum to intensify the effect.

A phaser can have a variety of different parameters, but the rate will always refer to the time it takes for the modulation to complete one cycle, meaning that the all-pass filter has swept the frequency spectrum one time and returned to its original position.

A phaser plug-in will often give the producer control over the number of all-pass filters, referred to as stages, and how much of the frequency spectrum those stages cover as they sweep up and down.

Just like the other effects plug-ins I’ve covered, a phaser should be used in moderation, as it can have an enormous impact on the sound of a track, though it can be quite useful for making things sound more interesting when a mix absolutely needs it.