Synthesiser Basics: Part 1 – Oscillators

Synthesiser Basics: Part 1 – Oscillators

In this multi part series we break down the basic functions of an analog synthesiser and look at the way these functions interact to create sound.

It’s a damn good time to be alive if you’re into making music with synths. Forward thinking companies such as Korg and Arturia have been at the forefront of the portable/affordable analog synthesiser movement with the release of the Volca and Brute range respectively. Synth stalwarts Roland, Moog and Dave Smith are re-envisioning classic products for a modern audience, while the development of eurorack modules continue to grow at an exponential rate. The second-hand synth market has also seen healthy growth with the creation of Facebook marketplace and the number independent vintage resellers on the rise.

Yes, it’s a damn good time to be alive. But for those just getting started, even the simplest hardware synth can be a confusing and problematic device. What seems simple isn’t always so. Take this common phenomenon. You buy your shiny new synth and are ready to make some Kraftwerk-esque sounds. You plug in some headphones, turn it on, crank up the volume, start banging on the keys … and … nothing!? Or even worse something that sounds terrible. So you take some time to look at the plethora of knobs and sliders on the device and then the panic sets in.

First, you notice series of acronyms: VCA, VCF, LFO…huh!?. You keep searching for something familiar but instead are confronted with envelopes, aren’t they used for mailing letters? The envelopes are accompanied by some equally unfamiliar terminology, Attack, Decay, Sustain and Release (or ADSR). By the time you are reading the words modulation, cutoff and resonance the panic starts has turned into straight up anger and frustration.

But fear not. In this series of articles we will be exploring the general makeup and functioning of analog synthesisers for those looking for some help getting started.

Oscillators

The starting point on any synth is the sound generation. The synthesiser component responsible for producing sound is the oscillator. In order to fully appreciate the way in which an oscillator operates, it is important to have a basic understanding of the fundamental properties of sound. In short, sounds are simply changes in air pressure created by a vibrating object (plucking a guitar string for example). These changes in air pressure vibrate our eardrums, which subsequently results in our perception of sound. In the world of synthesisers the generation of vibrations is referred to as oscillation (created by the oscillator section of a synthesiser). Those oscillations repeat periodically, in patterns called waveforms. The size (amplitude), speed (frequency or pitch), shape and structure of a waveform can all be manipulated by utilising various controls on a synthesiser. While the sound of raw waveforms is far from inspiring, it is this manipulation which gives rise to an abundance acoustic possibilities – but more on that later.

Types of Waveforms

Often a synthesiser will allow you to choose the shape of the waveform that the oscillator produces. The most common types of waveforms are Sine waves, Square/Pulse waves, Triangle waves and Sawtooth waves. The type of waveform you choose to use depends on the sound you want to create. You can hear the differences between each of these waveforms here.

Frequency and Pitch

As well as the generating the shape, the oscillator section also controls the frequency of the waveform. Frequency refers to the number of wave cycles per second measured in Hertz (Hz). While frequency is closely related to pitch, the two are not identical. Frequency is an objective, scientific attribute that can be measured. Pitch on the other hand relates the subjective perception of whether a sound seems “higher” or “lower” relative to other sounds. Generally speaking, the higher the frequency, the higher it will sound.

Each musical note is denoted by a particular frequency, A4 (middle c) for example corresponds to a frequency of 440Hz. Conversely, an octave refers to a doubling or halving of frequency. For example, the A5 (one octave higher than A4) has a frequency of 880Hz while A3 (one octave lower than A4) has a frequency of 220Hz. You can find a list of musical notes and their frequencies here.

Synthesiser Basics: Part 1 – Oscillators
The Minilogue is the latest polyphonic analog synth offering from Korg.
Synthesiser Basics: Part 1 – Oscillators
The oscillator section of an original Minimoog Model D via Matrixsynth
Synthesiser Basics: Part 1 – Oscillators
Sine, square, triangle, and sawtooth waveforms via Wikipedia

Polyphony

Polyphony pertains to how many notes a synthesiser can play at any one time. Synths like the Minimoog are monophonic – meaning they will only play one note at a time. Synths like the MicroKORG are capable of 4 voice polyphony so you can play chords.

Multiple Oscillators

Larger synthesisers may have more then one oscillator on board. The Arturia Matrixbrute for example, has three oscillators. However, multiple oscillators should not be confused with polyphony. The Matrixbrute is still a monophonic synth. This means that all three oscillators are triggered each time you play a note. The advantage here is that the three waveforms may be combined to create a richer, fatter and more tonally complex sound then could be achieved on a single oscillator synth.

So now we understand the basics of how a synthesizer generates sound.In Part 2 of this series we will be looking at the concept of subtractive synthesis and how filters are used to create interesting and harmonically diverse sounds.

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