In BlokDust, Envelope is a pre-effect. It shapes the sound of a Source block by setting the Attack Time, Decay Time, Sustain Level, and Release Time (ADSR).
Attack Time affects how much time it takes for a sound to transition from silence to full volume (peak). Decay Time sets how long it takes to transition from peak to the sustain level. Sustain Level is the volume the sound then remains at until it’s released. Release Time is the time it takes for the sound to transition back to silence after it’s been released.
The Envelope options visualises the envelope contour, and allows you to set the ADSR with draggable markers.