A synth whose circuitry is specialized for the purpose of producing string and pad sounds. A number of string synth models were produced in the 1970s; at the time, the circuitry needed to produce a general-purpose polyphonic synthesizer was costly. However, several circuit designers discovered simplified, non-voltage controlled oscillator circuits which could be produced cheaply, and which by happy coincidence were fairly good at imitating the sounds of massed strings — something that performers of the time were looking for in a polyphonic synth. Further, newly developed chorusing circuits helped these circuits produce a more pleasing sound. The circuitry was inexpensive enough that many were made fully polyphonic, or at least paraphonic, fulfilling the desires of performers to be able to play chords and harmony.
The Dutch organ maker Eminent introduced what is considered the first string synthesizer in 1972, although some of the concepts were based on circuits that had been used in electric organs since the 1960s. The synth was contained within the company's model 310 organ. It used a divide-down oscillator architecture which produced two basic waveforms, an octave apart. Extensive use of chorusing circuits, based on the then-new BBD analog delay devices, gave it a thick, pleasing sound. It was also possible to overlay it with sounds from the organ circuitry. Since the 310 was marketed for home use, its visibility among pro musicians was limited, but Jean-Michel Jarre used one extensively on his Oxygene album.
After 1973, a variety of manufacturers jumped into the market, including Freeman from the UK, several organ makers (including Eminent itself, marketing its synths under the name of Solina), and synth manufacturer ARP. The typical string synth contained some type of master oscillator circuitry (either divide-down or top-octave division), some very basic filtering to allow for some timbral variation, a basic envelope generator and VCA capability to allow for some sustain and make the attack and release less organ-like, and a chorus circuit, all of which could be manufactured at a reasonable cost for the day. Oftentimes, the chorus (or "ensemble") circuits were the key to getting a good sound out of the device, as the basic oscillator timbres tended to be rather static. Most models incorporated a few presets for different string- or woodwind-type sounds which were often labeled with names such as "violin", "viola", "clarinet" or "saxophone", even though the actual sound usually bore only a passing resemblance to the named instrument. Sound editing capability was rare to non-existent.
String synthesizers fell out of favor in the 1980s when proper polyphonic synthesizers became less expensive. Recently, there has been something of a resurgence in string synths, as performers have discovered certain subtle properties of the vintage units that are difficult to duplicate on other synths. No new string synths have been manufacturered to date, but many vintage units have been restored (they were manufacturered in large numbers, so prices on vintage units aren't too high), and several soft synths have been produced which emulate string synths.