Even if the first modular synth was developed by Harald Bode in the late 1950s the origin of Modular Synthesis goes back to the 60s with Don Buchla on the West coast and Robert Moog on the East coast.

Buchla tended to not refer to his instruments as synthesizers, since the name connotes imitating existing sounds and/or instruments. Rather, his intent is to make instruments for creating new sounds, avoiding the use of keys so that the musician isn’t playing traditionally… While Moog was interested in making playable devices for performers in the mainstream.

Modular Synthesis gives the ability to connect or “patch” modules together in whatever way the composer wants in order to create unique, never-before-heard sounds, constructing unique signal paths capable of synthesizing sounds Whereas in self-contained, non-modular gear, there are hardwired connections under the hood and the functionality is relatively fixed regarding the number of oscillators, LFOs, envelopes, etc., that are built into the device. With modular, there is the ability to expand the system in infinite ways, simply by adding more modules. Devices control are controlled by other devices by means of CV (control voltage), the lifeblood of modular. Patch cables are used to send voltage throughout multiple units interacting with one another – with signal generators used to create sound that is then passed through a labyrinth of oscillators, envelope generators, filters, voltage controlled amplifiers and sequencers.

Here are the main components of a system:

  • Case and Power Supply – Euroracks are typically in rows of 3U or 3 rack spaces each and measured horizontally in terms of HP (horizontal pitch). Typical widths are 84 and 104 HP. Obviously, more room in a rack will lead to more investment, because no one likes an empty space in their rack. Some racks come with built-in power and some will need a power supply purchased separately. The investment in a rack is typically one of the largest cash outlays and should not be taken lightly. Try to project your future needs and portability requirements before making a choice.
  • Oscillators or Full Synth Voices – The number of voices is how many notes you can play at once. This is the polyphony. Each voice is made from a number of oscillators. An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave.[Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. An oscillator can be designed so that the oscillation frequency can be varied over some range by an input voltage or current: Voltage Controlled Oscillator.
  • VCFs – Voltage Controlled Filters – A voltage-controlled filter (VCF) is an electronic filter whose operating characteristics (primarily cutoff frequency) can be set by an input control voltage.[1] Voltage controlled filters are widely used in analogue music synthesizers. A music synthesizer VCF allows its cutoff frequency, and sometimes its Q factor (resonance at the cutoff frequency), to be continuously varied.
  • Envelope Generators – Envelope Generators are circuits that, when triggered, produce a contoured signal over time. Often used to control volume, EG’s can give a natural or unnatural character to a played note by giving the synthesist control over how fast the volume rises from silence to full volume, also known as the Attack Phase as well as how long it takes for the sound to fade out after a key is released, also known as the Release Phase. These parameters enable you to determine whether your notes will sound like a click with a fast attack and a fast release, a percussive sound with a fast attack and a slower release, or a sound that fades in with a long attack. You will often find EG’s with more phases such as the classic ‘Attack, Decay, Sustain, Release’ paradigm. ADSR.
  • LFOs – Low-frequency oscillation (LFO) is an electronic frequency which is usually below 20 Hz and creates a rhythmic pulse or sweep. Audio effects such as vibrato, tremolo and phasing are examples.
  • VCAs – Voltage Controlled Amplifiers – An amplification circuit whose gain is controlled by an external voltage. VCAs are commonly used in synthesizers to create the volume envelope of sounds.
  • Utility and other modules which may include:
    • Multiples for duplicating a signal
    • Mixers
    • Waveform Processor
    • Slew Limiter
    • Effect Processor (Delay/Reverb, etc.)
    • Clock divider
    • Attenuverters
    • Random Voltage Generators
    • Interface modules for getting MIDI and/or Audio in/out
    • Loads of cables…

One can plan his system on Modulargrid platform.

A glossary of terms and many great resources thru their pages:

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