A synthesizer that uses a guitar, rather than a keyboard, as its controlling interface. Guitar controllers can be divided into two categories, those that use a conventional guitar with pitch converters detecting the notes played, and those that directly detect the hand motions of the player with touch pads and sensors. (The latter type generally produce no sound of their own, and often bear little resemblance to a conventional guitar.) Guitar synthesizers have always proven difficult to design and have often disappointed both their makers and their users; design of the pitch converters for systems that use conventional guitars has proven to be hugely problematic. (Development costs of the Avatar, one of the first guitar synths, are reputed to be what put the ARP Instruments synthesizer company out of business.) As a result, after an initial burst of enthusiasm in the late ‘70s, guitar synths have never achieved the popularity that some manufacturers anticipated. However, Roland has kept at least one model in production throughout, and recently Parker and other guitar makers have been marketing a “MIDI guitar” — a guitar with a pitch converter built-in and a MIDI jack right on the guitar body, so that it can control a conventional synth without a separate converter box. Other string instruments have also been interfaced to synths, notably the violins and other bowed string instruments marketed by Zeta and Barcus-Berry.