“AD” or “Attack Decay” refers to a type of envelope generator that shapes the amplitude or other parameters of a sound over time by providing a control voltage (CV) signal. An AD envelope generator is a simplified version of the more common ADSR (Attack, Decay, Sustain, Release) envelope, consisting of only two stages: Attack and Decay.
- Attack: This is the first stage of the AD envelope, during which the control voltage rises from its initial value (usually zero) to its peak value. The attack time determines how quickly this rise occurs, with shorter attack times producing a faster, more immediate onset of the sound, and longer attack times creating a slower, more gradual increase in amplitude or other parameter.
- Decay: This is the second and final stage of the AD envelope, during which the control voltage falls from its peak value back down to its initial value. The decay time determines how quickly this decrease occurs, with shorter decay times producing a faster, more abrupt decay, and longer decay times resulting in a slower, more gradual fade-out of the sound.
An AD envelope generator can be used to modulate various aspects of a synthesizer’s sound, such as the amplitude, filter cutoff frequency, or modulation depth. By adjusting the attack and decay times, a musician can shape the dynamic characteristics of a sound, creating anything from sharp, percussive hits to softer, more sustained tones. AD envelope generators are commonly found in both hardware and software synthesizers, as well as in modular synthesizer systems.