A we saw briefly in the last blog, an LFO was used to modulate the VCF, causing a nice pulsing or throbbing sound.

So what is an LFO?

A Low Frequency Oscillator (LFO) is exactly what it says on the tin. Its typically so low frequency waveform - sinusoidal, triangular, saw or pulse, that its inaudible directly. However its heard when its used to modulate another component. We can call it a carrier or modular oscillator rather than an audio oscillator. The notion of carrier waves and inaudible oscillators modulating other components is also the basis of Frequency Modulation (FM) synthesis. Buts thats one for another day.

In this case, I found a nice, simple LFO circuit based on a single TL074 quad op-amp from David Haillant which I made a very minor modification to, by swapping a single LED with a bi-colour LED to indicate when the wave form swings positive (green) and negative (red).

This module provides 3x key controls and a single CV output.

• Frequency or rate of the oscillator
• Depth or "swing" of the wave, point to point 10v range (max) +5 to -5.
• Waveform; triangle or pulse/square

Pretty tidy!