Abstract: An envelope generator for an electronic organ, especially for developing percussion sounds, in which each of at least some of the organ cases having keyers pertaining thereto are provided with envelope control circuits interposed between the keys and the respective keyers. Each envelope control circuit includes voltage supply means connected to the keyer and a control circuit therefor which is actuated by depression of the key. The control circuit provides for continuous actuation of the keyer by voltage from the voltage supply means while the key is depressed or for a momentary supply of keyer actuating voltage from the voltage supply means to the keyer followed immediately by a decay of the keyer actuating voltage at a predetermined rate and which rate can be selectively varied.