Digital control of attack and decay

In a digital electronic organ or the like external waves of controllable duty cycle are used to control the on time of a field effect transistor (FET) through which a capacitor is charged. A similar rectangular wave of controllable duty cycle is applied to a second FET to control the on time thereof for controlling the discharge of said capacitor. The state of charge of said capacitor is used to control the conductivity of yet another FET through which a desired frequency is conducted to effect enveloping of such frequency with the desired attack and decay characteristics.