SONICALLY, flangers sound like the lovechild of chorus and phaser, adding a sinister metallic quality that makes them popular with metal bands such as, erm, Metallica.

As with chorus and phaser, the flanger generates its trademark sound by splitting the signal from your guitar into a dry uneffected half, and a wet signal that has a smidgen of delay. The delay times involved are shorter than in a chorus effect, with a typical duration of just a few milliseconds.

When the dry and delayed signals are blended together again, phase interference between them causes harmonically ordered gaps or ‘notches’ to appear in the frequency spectrum. The position of these notches is then swept up and down by a low-frequency oscillator (LFO, controlled by the rate knob) that alters the delay time of the wet signal – just like a phaser.

This produces the characteristic swirling sound. Flangers differ from phasers because the notches in the flanger signal are equally spaced across the frequency range.

Flangers produce a roiling, churning tone that is distinctively cold. Many flangers feed some of the blended output signal back into the input of the effect to add even more metallic, resonant overtones.