Percussion envelope generator

Abstract

A circuit for generating a percussion envelope for use in electronic organs and similar electronic keyboard instruments wherein the envelope has an attack overshoot, a long decay, and a snub decay when the key is released. A velocity sensing feature is included, whereby the force with which the key is struck determines the amount of capacitor discharge, and the voltage remaining on the capacitor is compared with the amplitude of the attack portion of the envelope such that decay is initiated when a compare condition is reached. A second comparator sets the amplitude at which the envelope undergoes transition from a fast decay to the normal long decay. The timing for the attack and three decay portions of the envelope are independently controlled by means of four clock driven electronic gate circuits which incrementally charge and discharge the main timing capacitor. The gate circuits include a pair of serially connected field effect transistors having a capacitor connected at their juncture. The timing control for each individual keyer, including all of the timing capacitors, is contained within a separate LSI chip.