The A to Z of analogue synthesis

Minimoog Model D
(Image credit: Future)

If you're looking to learn the fundamentals of synthesis, analogue is the best place to start. 

These machines form the basis for the way that almost every other type of synthesizer operates, so an understanding of the terminology used to describe their basic architecture is an essential part of synthesis 101. 

Read on to learn your VCOs from your VCAs and get acquainted with analogue synthesis.


The word "analogue" in the phrase "analogue synthesis" refers to the method of sound generation. Analogue synths use analogue circuits and signals to produce sound electronically, through the manipulation of voltages running through those circuits. This stands in contrast to digital synths, which use DSP (digital signal processing) and computer chips to generate sound. 


BPF stands for "band-pass filter". This VCF (voltage-controlled filter) allows a narrow band of frequencies to pass through the signal, filtering out the frequencies above and below the cutoff.


CV stands for “control voltage”. It’s a fundamental tool for
sending essentially analogue “information” from one source to another. CV can be notes in a scale, triggers for turning events on and off, modulation, and more! 

In the Eurorack realm (or most semi-modular synths), each octave in a scale is represented by 1 volt of electricity. So if you write a 2 octave arpeggio, it will span 2 volts of electricity.


DCO stands for “digitally controlled oscillator”. This is essentially the same as a VCO, and still produces analogue sound, but is controlled by a digital input, rather than via CV, for more stable tuning.


An envelope is a contoured CV. It’s typically broken up into multiple sections that define its “shape”. These sections typically include attack, decay, sustain, and release. All four of these sections can shape fast plucky sounds, to soft gentle pads. Some envelopes are even simpler with just an attack and decay setting. 

Some envelopes can trigger a gate event after each phase of the shape. For instance, once the attack part is complete, a gate can be triggered to signify that portion of the envelope is complete and trigger another envelope to start for a modulation source.


Eurorack is a standard of modular synthesis invented by Dieter Doepfer. This standard, which has now been widely adopted by most modular brands, set guidelines of how much voltage Eurorack modules could receive, the overall size of the gear, the power requirements, and jack sizes for receiving and sending voltage/audio/etc.


FM synthesis stands for frequency modulation synthesis. This process involves taking one VCO and modulating its signal with another VCO, or other complex CV signals. This can also create harsh, metallic tones and interesting textures.


HPF stands for “high-pass filter”. This type of VCF is just like the LPF, but in reverse. Frequencies above the cutoff point will pass through and be heard. Meanwhile frequencies below will be filtered out.


LFO stands for “low frequency oscillator” and is the most common source of modulation. Most basic synthesisers come with at least one LFO to help create moving sounds. 

Basic LFOs usually have a sine or triangle wave shape, and a square wave to patch out. Some can be synced with a gate to start the LFO each time a gate trigger is received. Good quality VCOs can also double as LFOs, assuming their tuning can go low enough. 


LPF which stands for “Low-Pass Filter”. This type of VCF (voltage-controlled filter) will allow any frequencies below a certain level to pass through the signal to be heard. Frequencies above the filter cutoff point will gradually be filtered out of the signal.


MIDI stands for Musical Instrument Digital Interface, and it's a technology that gives us a way to send notes, synchronise, and send other information between instruments both analogue and digital, communicating between two machines or over a larger network. 

MIDI clock

A MIDI timing signal that's used to synchronize MIDI-enabled equipment, so that the devices can play in sync. 


Modulation is when the input of one parameter is adjusted (over time) from the output of another. In the analogue/modular world this is done using CV. 

Synthesis is built on modulation. Sources getting adjusted from other sources is probably the simplest way of describing synthesis, and you (the synthesist) are the ultimate modulator.


Modular/semi-modular are types of synthesiser that can be rerouted by the user. Typical self-contained synthesisers – a Minimoog, for example – are pre-wired, so the connection between its oscillators, filters, amps, etc cannot be changed by the user. 

A modular synth is made up of totally distinct elements – aka modules – each of which usually specialises in a specific role, such as a filter, oscillator or envelope. In modular systems these could come from a variety of different brands, and can be freely swapped and connected by the user. 

A semi-modular synth is a middle ground between the two – it is a self-contained instrument, and will usually create sound without the need for user-created connections, but its elements can be reconfigured or connected to external gear. This is done through the inclusion of a patchbay – a selection of individual inputs and outputs available at various points in the synth’s signal path.


The terms monosynth and polysynth refer to how many voices a synth has, ie, how many notes/pitches it can generate simultaneously. A monosynth is only capable of generating a single note at any one time, as it is monophonic.


In synthesis, the term noise is used to refer to one of a few specific variations of a random audio signal, which produce a sound comparable to TV static. This signal can be used to add colour to a sound, or used to randomly modulate other signals.

Noise comes in a few variations, but the term usually refers to white noise by default, unless specified otherwise. White noise contains all the frequencies in the audible range (20Hz-20kHz) sounding at equal power. 


Notch filter is probably the least common type of VCF (voltage-controlled filter). It’s usually used in traditional equalizers, but can occasionally show up in VCFs. It basically does the opposite of the BPF, by rejecting any frequencies from the signal at the cutoff point.


A term used to denote a synthesizer where multiple oscillators are used to play different notes, but all of those oscillators are sent through the same signal path, going through the same VCF and VCA - as opposed to polyphony, where each oscillator runs through its own filter and amplifier. 


A patch is a configuration of parameter settings and signal routings that, combined together, generates a particular sound on a synthesizer. In modular synthesis, sounds are produced by using patch cords to send signals from one module to another - this is where the term comes from.


In contrast to a monosynth, a polysynth can simultaneously produce multiple pitches in accordance with how many voices it offers. This allows it to create a polyphonic output – ie, chords. 


Sequencers generate a series of control voltages and gate signals that are are used to create repeating patterns of notes when programming melodies, harmonies and rhythms. 


Subtractive synthesis is the process of subtracting frequencies from a signal, usually with a VCF, to create a new signal. Combining multiple VCOs and then patching a VCF to “subtract” some harmonics is by nature, subtractive synthesis.


Trigger/Gate is a type of CV that signals an event to be “activated”. If you’ve played a synthesiser keyboard, every time you press down on a note, you’re creating a trigger event in the keyboard to activate that particular note. 

Gates are used to trigger all sorts of events in modular gear, from notes in a sequencer, starting LFOs, signaling stages of envelopes, and more. In terms of actual voltage, gates usually represent either low voltage or high voltage, creating a binary on/off scenario.


VCA stands for “Voltage Controlled Amplifier” and is often paired with an envelope. VCAs take a CV, usually from an envelope, and amplify a signal with the contour
of the CV. Most synthesisers have a VCA at the end of the signal
chain to finalise the shape of the sound. 

VCAs can be used to shape modulation sources, in conjunction with envelopes, to create complex modulations.


VCF stands for voltage-controlled filter, and is the most common element or module for shaping sounds. Filters work by cutting frequencies from a signal. There are a few fundamental types of filters: LPF, HPF, BPF and Notch.


VCO stands for “Voltage Controlled Oscillator” and can also just mean oscillator in the analogue world, or osc for short. The VCO is a building block for sound generation because it literally self-oscillates continuously while it is powered on. 

The VCO will accept a CV for pitch control. In terms of Eurorack, it’ll be 1 volt per Octave. Most VCOs output multiple waveforms. The most basic is a Sine, Triangle and Square wave. Most VCOs offer at least these fundamental shapes for synthesis.

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