The oscillator is the main sound generation module. It produces a waveform (a pattern of vibrations in the air) that repeats – “oscillates” – at a certain frequency, which is the pitch of the note it is playing. A Voltage Controlled Oscillator allows you to set that pitch with an incoming voltage. The most common standard is for a change in 1.0 volts to result in a change of one octave in its tuning (Buchla modules use 1.2 volts per octave; with “linear” oscillators a change of 1 volt results in a change defined by a constant number of cycles per second, rather than a musical interval such as octaves). Tuning controls on the front of the module set the specific pitch you will hear for a specific voltage.
Oscillators may use either digital or analog circuitry. Analog oscillators tend to produce a limited set of classic waveforms, including a pulse or square wave, a sawtooth or ramp, a triangle, and maybe a sine wave. You will sometimes hear oscillators described as having a triangle or sawtooth “core”; this describes the internal circuitry: it may be designed to primarily create a specific waveform, and then the other waveforms are derived from that. Digital oscillators tend to produce a far wider range of waveforms, and may even use alternate synthesis techniques such as modeling a vibrating string or vocal path.
The biggest weakness with voltage controlled oscillators is how well their pitch tracks the incoming voltage. Some oscillators go out of tune after just an octave or two; some can keep accurate pitch or “intonation” across multiple octaves. Analog oscillators tend to be more susceptible to this than digital ones. Allowing your synthesizer to warm up for 20-30 minutes can help stabilize its tuning.« Back to Glossary Index