The ESP-20 Processor recreates the slightly bizarre and endlessly useful External Signal Processor section of the classic MS-20 synthesizer. The Frequency To Voltage converter analyzes incoming audio and generates matching voltages for controlling oscillator pitch and envelope amplitude. This lets you "play" Voltage Modular by singing, playing guitar, or any other monophonic signal source. ESP-20's frequency converter has a much wider range than the original for increased functionality, while still retaining the quirkiness of the original.