Attack is the envelope’s opening move. Percussion arrives in a millisecond; a bowed note takes fifty or more; a reversed pad may take seconds. The ear sorts gestures by attack before anything else, sharp meaning strike and slow meaning swell.
The same word names a control on dynamics processors and followers: how fast the device reacts when level rises. A fast attack catches transients, a slow one lets them through, and the setting is one of the most audible choices in production.
Reactive systems inherit both meanings. An envelope follower with fast attack and slow release makes visuals strike and then breathe out, the closest thing motion design has to a universal musical gesture.