At the heart of the synthesizer lies the oscillator. The oscillator section is the sound source of your synthesizer and allows you to define the initial pitch and spectrum of your sound.
Oscillators create a repeating waveform at some frequency. This is very similar to what happens in acoustic musical instruments. As we excite a resonant object, such as a guitar string, it vibrates at some frequency, governed by the length of the string. This, in turn, produces a sound with a unique spectrum, governed by the size, shape and construction of the instrument. Oscillators give us a way to mimic this phenomenon, creating our own sounds from scratch.
Almost every synth offers an oscillator section with the basic parameters we discussed in Basics: Subtractive synthesis. However, it is not uncommon to come across a synth that offers additional parameters in the oscillator section that allow you to shape the tone of your synth.
Almost all synthesizers allow you to choose between multiple waveforms on either one or multiple oscillators. Each waveform has its own spectrum, and will respond differently to specific synthesizer techniques like resonant filter sweeps and wave shaping (link to article). The most common waveforms you'll come across are:
- Sine (a simple sine wave, the most basic waveform without overtones)
- Square (a more metallic sound, adjustable with the pulse width setting)
- Triangle (a soft, warm tone)
- Sawtooth (a sharp bright tone that is ideal for filtering)
- White noise (all frequencies, presented at equal power)
- Pink Noise (all frequencies, presented with less power in the higher frequencies)
Oscillator sync is a way of making two oscillators work together. We refer to a single journey through the positive and negative stages of a waveform as a cycle or period. Check out this article if this sounds unfamiliar to you (link). Oscillator sync utilizes a master oscillator and a slave oscillator. The master oscillator forces the slave oscillator to reset every time it completes a cycle. The result is that no matter what the pitch of the slave oscillator is, you will always hear the pitch of the master oscillator. Because the cycle of the slave oscillator is cut short before/after a complete cycle, irregular wave shapes are created, resulting in a more complex timbre.
A sub-oscillator is an oscillator that plays an octave (or two) lower than the main oscillator. Its pitch cannot be changed independently of the main oscillator. It is often a square or triangle wave. Usually the sub-oscillator is used to fatten up a sound, with the lower fundamental adding support in the bottom octaves and the harmonics (especially for a square wave) adding thickness to the low midrange. Keep in mind that too much low end can make a sound harder to place in the mix.
Noise waveforms are unlike other waveforms because they create a random mixture of frequencies rather than unique pitches. Some synthesizers have different types of noises available, which will have varying frequency balances. White noise is the the most common noise. Pink, red, and brown noise are darker. Blue noise tends to be brighter. One of the musical uses for white noise is to use it percussively, like for an electronic snare sound or trance lead. Another one is to make a synthesizer sound "older", and works especially well with a triangle wave. One last example would be to use it for FX-type sounds, like wind or explosions. By passing the noise through a filter and envelope we can shape it dramatically, helping it to fulfill its purpose in a musical context.