A Low-Frequency Oscillator is based upon an electronic audio signal that is used to create a sweep or rhythmic pulse, usually set below 20Hz (slower than normal VCOs – voltage controlled oscillator). This sweep or pulse is then used to modulate other components within the synth.
LFOs are not actually audible to the human ear, instead, they are used to influence other parameters in the synth. For example, you can set them to modulate the pitch of one of the VCOs, the more you increase the LFO, the more the VCO will start to wobble in pitch.
The shape of this pitch-wobbling will look like a smooth wave, curving up and down, this is due to the LFO being set to a sine wave. Many LFO’s have various waveforms including saw, square and random. Choosing any of these will alter the amount of pitch movement in the VCO.
As we mentioned, LFOs are not audible as they are not within the human ears frequency range. However, some of the more advanced LFOs can actually be sped up (increased in frequency) to over 20Hz, this process is known as audio-rate modulation.
LFOs have many effective uses and can bring your music to life with different sound properties. Use them on the amplifier and you’ll hear a tremolo effect, use them on a filter and you’ll be able to modulate the timbre of your sound, known as filter modulation.