LFO

An LFO, or low frequency oscillator, is a circuit that modulates another part of a pedal's signal path at slow speeds¹,². In phasers, it changes the position of the all-pass filter stages to produce the swirling effect¹, and in flangers it modulates the timing of the delay to create a sweeping, whooshing sound². It also drives tremolo, for example by modulating the bias voltage of an amplifier's tubes³, and appears in delays, chorus, vibrato, and fuzz synth pedals as a source of filter, pitch, or timing movement⁴,⁵,⁶,⁷,⁸. The waveshape and sweep range of the LFO are among the biggest factors in how a phaser sounds⁹, and some pedals offer selectable LFO shapes¹⁰.