A type of synthesizer developed in the 1950’s and popularized in the 1970’s in which the components, such as controllers, oscillators, filters and amplifiers are designed as separate devices and interconnected by patch cords. Every module has input and output sockets that are used for interconnecting with the others. They don’t have MIDI capabilities, memories, or presets, and they very rarely have hard-wired internal connections, all connections being “modular” via patch cords. The underlying principle of modular synthesis is voltage control, used to control VCOs, trigger an ADSR envelope. Also, in modular synthesis, there is little or no difference between audio and modulation signals, e.g., the audio output of a VCO can be used to modulate the control input of a second VCO, and a mixer can mix control voltage signals just as an audio mixer would.