Phase shifters (or phasers) and flangers get their sound by creating one or more notches in the signal's frequency. The notches are created by filtering the signal, and mixing the filter output with the input signal. The filters can control the location, number of notches, and width of the notches.

Most phase shifters start with a simple filter, then add more filter stages to create more notches. A stereo phaser uses two filters with notches at different frequencies. You can also create more complex sounds by mixing the outputs of the two filters. This can give you virtually endless sonic possibilities. From subtle rotating-speaker effects, to swirling, edge-city sounds from classic 60's guitar solos, phasers can be a very useful addition to any player's arsenal.

Flangers produce the unmistakable jet-engine "whooshing" sound. Basically a type of phasing, a flanger creates a set of equally spaced notches in the audio spectrum. Phasing also uses notches, but multiple filters and user controls create random spacing.