An oscillator is a repeating signal that creates waveforms, like sine waves, square waves, triangle waves, etc. These waveforms can be used to create sounds, or used to control other parameters of the synthesizer through low-frequency oscillation.
The Oscillator is the heart of the synthesizer. Without them you would hear no sound. The original sound is started within the oscillator and is then fed through the rest of the signal path. You can have one oscillator (monophonic), two (duophonic) or multiple (polyphonic) oscillators.
The term oscillation is used when an oscillator produces a waveform, the resulting sound is dependent on the shape of this waveform. These waveforms are continuously oscillating and are determined by the speed and pitch of the note. Each waveform has a unique timbre/tone.
The common oscillator waveforms are called sine, saw, square, pulse and triangle. Sine waves have smooth characteristics that rise and fall in the shape of an “S”, producing a soft tone. Saw waves give a sharp and harsher tone, their waveforms resemble the teeth on a sharp saw.
Square waves produce a hollow-like sound and their waveforms are shaped with near enough 90-degree angles like a square. Pulse waves are similar to square waves, only they are usually half as wide and have the potential to be modulated via “Pulse Width Modulation”.
Lastly, triangle waves have triangularly shaped waveforms with their tone falling in between saw and sine waves. On their own, these waveforms can produce all sorts of different tones but you can also mix them together to make even more complex sounds and shapes.
The LFO (low-frequency oscillator) is a unique type of oscillator. You can’t actually hear the LFO because it oscillates at frequencies below the range of human ears. LFOs are used to modulate other sections of the synthesizer, like frequency of filters or pitch of other oscillators.
LFOs use the standard waveforms as mentioned above, but due to the lower frequency in which they oscillate with the LFO, you can hear unique characteristics. For example, being able to notice the rising and falling of a sine wave, allowing for great detail when shaping sounds.
There are many more ways of using oscillators to help you adapt your music, especially when you begin to tune different oscillators in various ways, this opens up a whole new world of weird and wonderful sounds.