Modular synthesizer

The modular synthesizer is a type of synthesizer consisting of separate specialized modules. The modules are not hardwired together but are connected together, usually with patch cords, to create a patch. The voltages from the modules may function as audio signals, control voltages, or logic conditions.

Development
The first modular synthesizer design was presented by Harald Bode at the 1960 AES convention, also attended by Bob Moog. This was the first patchable modular system with control voltage capability. The earliest commercial modular synthesizers were developed, in parallel, by Moog, and Buchla in 1963.

Other versions were soon to follow: EMS in 1969, ARP in 1970, Serge in 1974, and Roland came out with the Roland System 100 in 1976.

Also in the early 1970s, there were at least two mail-order electronics kit vendors Paia Electronics, and Aries, marketing different lines of simple DIY modular synthesizer systems. The Aries 300 Music System was modeled on the circuits produced by Bernie Hutchins and published as Electronotes. In the 1980s in the UK the Digisound 80 modular synthesizer, designed primarily, by Charles Blakey was sold as a kit by the company Digisound Ltd.

In the late 1970s, modular synthesizers started to be largely supplanted by highly integrated keyboard synthesizers, racks of MIDI-connected gear, and samplers. However, there continues to be a loyal following of musicians who prefer the physically patched approach, the flexibility and the sound of traditional modulars. Since the late 1990s, there has been a resurgence in the popularity of analog synthesizers spurred on by physical standardization practices, an interest in retro gear, decreased production costs and increased electronic reliability and stability.

These days hardware offerings range from individual modules through complete systems in cases to kits for hobbyist DIY constructors. Many manufacturers augment their range with products based on recent re-designs of classic modules, the original patents having lapsed. Many hobbyist designers also make available bare PCB boards and front panels for sale to other hobbyists.

Technical specifications
A modular synthesizer has a case or frame into which arbitrary modules can be plugged. Modules are usually connected together using patch cords. A system may include modules from different sources where these have the same form factor, and the same electrical connections.

Because control voltagess (CV) and audio signals are (usually designed to be) at the same level, almost any module can be connected with any other, and together with a variety of available selections and adjustments, a nearly infinite variety of sounds and effects can be produced. Reproducing an exact patch can be difficult or next to impossible.

Form factors
Many early synthesizer modules had modules with heights in integer inches: 11" (e.g., Roland 100), 10" (e.g., Wavemakers), 9" (e.g., Aries), 8" (e.g., ARP 2500), 7" (e.g., Polyfusion, Buchla, Serge), 6" (e.g., Emu) and width in 1/4" inch multiples. More recently it has become more popular to follow the standard 19" Rack unit system: 6U (Wiard), 5U (8.75" e.g., Moog, Modcan), 4U (e.g., Serge). Two rack 3U unit systems in particular are notable: the Frac Rack system (e.g., PAiA) and the similar Eurorack system (e.g., Doepfer). Further minor variations exist where European or Japanese manufacturers round a U measurement up or down to some closer convenient metric equivalent; for example the common 5U modules are exactly 8.75" (222.25mm), but non-American manufacturers may prefer 220mm or 230mm.

Electrical connections
Differences are with connectors that match 1/4-inch or 6.3mm jacks, 3.5mm jacks, and banana jacks, with main DC power supply (typically ±15V, but ranging from ±18V to ±12V for different manufacturers or systems), with trigger or gate voltages (Moog S-trigger or positive gate), with typical audio signal levels (often ±5V with ±5V headroom), and with control voltages of volts/octave (typically 1V/octave, but in some cases 1.2V/octave.) Most analog modular systems use a volts/octave system, sometimes termed linear voltage control; some (such as Korg MS-20, ETI 4600) use a volts/hertz system with excellent temperature stability but less flexible control.

Modules
Each module has its own simple function and they must be connected together with patch cords before any sound can be made. The sound of a patch depends on the interconnection of these modules and on their settings. Some cords carry the electrical version of the sound that will eventually be heard. This is the signal. Some cords carry instructions to modules about how to change the signal. These are controls. Some cords carry instructions about when modules should start their functions. These are triggers and gates.

Modules can be grouped by function, although there is some overlap. Most patches will involve at least one module from each group. Modules which can originate a signal are called sources or generators. The most common of these are oscillators and noise generators. Modules that can modify a signal are called processors or modifiers. The most common examples of these are amplifiers and filters. Modules that function primarily as sources of control voltages and triggers are called controllers or transducers. Controllers may be preset, such as envelope generators and low frequency oscilators, or they may be playable, like keyboards.

Semi-modular synthesizers
A semi-modular synthesizer is a collection of modules from a single manufacturer that makes a cohesive product. Modules may not be swapped out and often a typical configuration has been pre-wired. However, mechanisms are provided to allow the user to re-order the connections between modules.

Matrix Systems
Matrix systems use pin matrixes or other crosspoint switches rather than patch cords. Historic examples with pin matrixes include the EMS' Synthi 100 and VCS-3, ETI International 4600, Maplin 5600. The ARP 2500 used a matrix switch.

Patch Override Systems
The different modules of a semi-modular synthesizer are wired together into a typical configuration, but can be re-wired by the user using patch cords. Some examples are the ARP 2600, Anyware Instruments Semtex, Cwejman S1, EML101, Evenfall Minimodular, Future Retro XS, Korg's MS-10, MS-20, MS-50, PS-3100, PS-3200 and PS-3300, Mungo Enterprises State Zero, and Roland System-100.

Electronically Reconfigurable Systems
Reconfigurable systems allow certain signals to be routed through modules in different orders. Examples include the Oberheim Matrix and Rhodes Chroma, and Moog Voyager.

Hybrid modular synthesizers
Hybrid synthesizers use hardware and software combination. Include the fully self-contained Arturia Origin, the Clavia Nord Modular and Clavia Nord Modular G2 which need an external computer to edit patches.