Oscillators are responsible for creating cyclic patterns that can be used to either modulate parameters or create tones that can be heard. Typically an oscillator will fall into one of two categories. LFOs or low frequency oscillators will cycle below 20 Hz. Anything over 20 Hz falls into the category of high frequency oscillator or HFO. These are used to produce audio and usually go up to 20,000 Hz. Humans can hear frequencies from 20 Hz to 20,000 Hz so it makes sense that there are two distinct categories.

LFOs can be used to modulate parameters like the frequency of an audio rate oscillator. This is known as FM which stands for frequency modulation. Amplitude modulation or AM is similar in the way that the amplitude of one signal modulates a parameter of the other. Both FM and AM can be done by either LFOs or HFOs