extending your synth

Modulation and LFOs

One of the most common ways to add to the basic synthesizer circuit is to add modulation, in this case an LFO (low frequency oscillator). Modulation is a general term describing a changing the property of sound over time. Modulation requires a source signal called a modulator that controls another signal called a carrier. Modulating sounds can add a sense of motion, dimension, and depth.

The simplest way to add modulation to our hex schmitt circuits is to use one voice to modulate the pitch of another voice, producing a changing pitch rather than a static pitch. Here is how that looks.

In the diagram above the voice that uses pins 5 & 6 is modulating the voice that uses pins 1 & 2. The result is a changing pitch for which you can change the base pitch of the tones and/or the speed of the oscillation.