AR [Attack/Release]

The two-stage Attack/Release envelope raises from 0 volts to its maximum level (usually 5, 8, or maybe even 10 volts) at a rate set by its Attack parameter, and then stays at that value for as long as the gate signal fed into the envelope generator stays high. Then when the gate signal goes back to zero, the envelope’s output also falls back to zero at a rate set by its Release parameter. (There is a separate type of envelope known as an AHD – Attack/Hold/Decay – where you specify a fixed time for the level to stay at its maximum, rather than pay attention to the gate signal.)