A string synthesizer or string machine is a specialized synthesizer designed specifically to make sounds similar to that of a string orchestra. Dedicated string synthesizers occupied a specific musical instrument niche between electronic organs and general-purpose synthesizers in the 1970s and early 1980s, until advances in digital signal processing technology allowed the production of inexpensive general-purpose polyphonic synthesizers and samplers, which made the existence of a separate type of instrument unnecessary.^[1]

The development of the string synthesizer was originally motivated by the need for a cheaper and more portable alternative to the Mellotron, which was itself a cheaper alternative to human string ensembles.^[2] The availability of string synthesizers was influential in adding string orchestration to popular music that would not otherwise be able to afford the use of a human string ensemble, and their characteristic sound, which was almost, but not quite, like that of a real string ensemble, was one of the distinguishing sounds of the era.

To keep costs down, string synthesizers typically used a frequency divider architecture similar to that of electronic organs, with the addition of specialized in-built vibrato and chorus effects to mimic the ensemble effect of multiple string instruments playing at once. Classic string synthesizers included the Freeman String Symphonizer, Eminent 310,^[3] Logan String Melody, Roland RS-101, Roland RS-202,^[4][5] Korg Polyphonic Ensemble S, Crumar Orchestrator (Multiman-S), Elka Rhapsody, ARP String Ensemble,^[1] Moog Opus 3 and the Vox String Thing (a rebranded version of the budget Jen SM2007 String Machine) and the Roland VP-330.