The late 60s saw the arrival of some of music’s great innovators. Hendrix, The Beatles, and Zappa all used dramatic new effects to manipulate their traditional instruments. Newly available electronic devices from Electro Harmonix, Jim Dunlop and MXR allowed them to create weird new textures and evolving environments. These original pedals and rack units are now highly sought-after, and can change hands for surprising sums of money, but convincing emulations are included with most fully featured DAW packages. Though most of them were originally developed for guitars, they can often be put to good use on a synth or bass line.
A Phaser effect, such as the Electro Harmonix Small Stone, delays an audio signal by a few milliseconds, by playing it through a bank of filters at prescribed intervals. The slightly delayed sound is then layered back over the original. This tiny, stepped delay creates a whooshing, sweeping effect as the sources overlap. Each time the signal passes through the filter bank again, the relative distance between the two signals shifts, stretching the delay and causing the sound to constantly shift and mutate.