Both AD (Attack Decay) and AR (Attack Release) envelopes are simplified versions of the more common ADSR (Attack, Decay, Sustain, Release) envelope, and they are used to shape the amplitude or other parameters of a sound over time in synthesizers. However, they have different characteristics and are suitable for different types of sounds. Here’s a comparison between AD and AR envelopes:
- AD envelopes have two stages: Attack and Decay. The Attack stage determines how quickly the control voltage rises from its initial value to its peak value. The Decay stage determines how quickly the control voltage falls from the peak value to the final level, which is typically zero but can be adjusted in some envelope generators.
- AR envelopes also have two stages: Attack and Release. The Attack stage is the same as in the AD envelope, determining how quickly the control voltage rises to its peak value. The Release stage is triggered when a note is released or the gate signal is deactivated and determines how quickly the control voltage falls back to its initial value.
- Trigger behavior:
- AD envelopes are typically re-triggered every time a new gate or trigger signal is received, regardless of whether the previous envelope cycle has completed. This means that if a new trigger is received during the Decay stage, the envelope will immediately restart the Attack stage.
- AR envelopes are gated, meaning that the envelope will remain at its peak level for as long as the gate signal is active. The Release stage is only triggered when the gate signal is deactivated, allowing for more control over the sustain duration of the sound.
- AD envelopes are well-suited for percussive sounds, plucks, or other transient sounds that do not require a sustained portion. They can also be used to create dynamic modulation of other synthesizer parameters, such as filter cutoff frequency or pulse width.
- AR envelopes are ideal for sounds that need more control over the sustain duration, such as pads, string-like sounds, or any sound where the duration of the note is determined by the length of the gate signal. They can also be used for amplitude or parameter modulation with a defined sustain level.
Both AD and AR envelopes offer a range of expressive possibilities in shaping the dynamics and articulation of sounds in a synthesizer. The choice between them depends on the desired characteristics of the sound and the specific application within a patch or sound design.