Modular synthesizers are one of the oldest types of synthesizers around, as well as being one of the most expensive and interesting. The philosophy of a modular synth is that it is made up of modules which are interchangeable, allowing new modules to be added with ease, as well as the customization of existing modules. Because of the constant expansion of most users modular synthesizers, many systems end up looking like a telephone exchange – this is often referred to as GAS (gear acquisition syndrome).

The basic modules within most modular synths are as follows:

  • VCO (Voltage Controlled Oscillator) – an analogue oscillator which outputs a set frequency by default, and has separate outputs for each waveform.
  • VCF (Voltage Controlled Filter) – an analogue filter which includes different filter types such as low pass and high pass, as well as dedicated outputs for each mode.
  • VCA (Voltage Controlled Amplifier) – an analogue amplifier module which usually includes the ability to combine multiple inputs as well as output a linear or exponential signal.
  • Envelope (Generator) – an envelope generator which alters the voltage over the shape of the envelope. The envelope can be connected to control any part of the synthesizer, such as the amplifier or filter.
  • LFO (Low Frequency Oscillator) – a dedicated LFO module is available from some modular synthesizer companies, but some choose to use existing oscillator modules set to a special ‘Low Frequency’ option instead.
  • Mixer/Multiples – utility modules used for mixing or multiplying signals to other parts of the synthesizer.

Many other modules exist depending on particular modular synthesizer brands, such as ring modulators, sample & hold modules, and slew limiters. Step sequencers are also commonly used in larger modular synthesizers to send trigger signals to any part of the synthesizer – this is one of the many advantages of modular synthesizers, as the sequencer could be routed to control any part of the synth, not just the oscillator pitch.

Trigger signals themselves are one of the key parts of modular synthesizers, as they control the functions of most of the modules. ‘CV’ stands for ‘Control Voltage’, and determines the pitch of the signal which is sent, to control the note played. This sort of signal would be sent by sequencers and controller keyboards. ‘Gate’ is also a form of CV, but is used to specify when notes should sound – but not how they should sound. This makes it useful for modules such as sequencers and envelopes, as they are not pitch-dependant.

Some modular synths are not designed to create new sounds, but to modify existing ones. Such systems are known as ‘FX’ or ‘filtering’ systems. Many other types of modular synthesizer exist, such as special systems built purely for vocoding, sequencing, or use of a Theremin. Again, this is one of the advantages to modular synthesizers, as they are completely customizable by the user.