Without oscillators, your synthesizer will make no sound (well, actually it can - but that's in a future article). Oscillators produce the original sound which you can hear in your patches, which is then fed through the rest of the signal path in the synthesizer. Oscillation itself is the production of a certain type of waveform, which produces a different sound depending on the shape of the waveform. The waveform is constantly ‘run' depending on the speed/pitch of the note - so if an oscillator is set to a low enough pitch you will eventually hear gaps due to the slow speed of oscillation (see LFO below). Common oscillator waveforms are:
- Saw Wave - shaped like the teeth on a saw blade, this produces a very common sharp, biting tone.
- Square Wave - looks like a (near) perfect square, produces a reedy, hollow sound.
- Pulse Wave - a variation on the above, the pulse wave is half as wide as a square wave, and has the unique ability to have its width modulated (called ‘Pulse Width Modulation').
- Triangle Wave - unsurprisingly shaped like a triangle, this sounds somewhere in between a saw wave and a sine wave.
- Sine Wave - a smooth rising and falling shape (like a horizontal ‘S'), this produces a mild, soft tone.
- Noise - not exactly a waveform, but a source of sound produced by a certain colour of noise.
To start off with, that's all you need to know. To spice things up a bit though, depending on the number of oscillators a synthesizer has (usually 2 or 3) you can mix waveforms together! And not only that, but you can tune them differently from each other. This tuning can occur in octaves, semitones, and also in cents - which is a 100th of a semitone, and adds a swirling ‘detuned' sound created by multiple oscillators which are cents apart from each other.
LFO, or ‘Low Frequency Oscillator' is a special kind of oscillator which oscillates at a frequencies so low you cannot hear it - unless you deliberately tune it into the standard hearing range. It is used to modulate other parts of the synthesizer, such as the pitch of an oscillator, or the frequency of the filter. LFOs still use standard waveforms just like oscillators, but because they operate so slowly the variation in time between the start and finish of the waveform is clearly noticeable - for example, with a sine wave you are able to hear the smooth ascending and descending nature of the waveshape. Used properly, this adds animation and a moving texture to the sound in your synthesizer.