Ambience activity is a sound source that simulates a dynamic activity based on an observed value. Activity is mediated via an activity curve that transforms the observed value into the level of sound activity. For example, the cricket sound in the swamp is such an ambience activity, tied to the sun intensity. It gradually fades in as sun intensity moves toward 0, and fades out when it moves back toward 1. Another sound is the rustling of the leaves, where more rustling occurs with increasing wind strength, and vice versa.
Ambience activity uses two stereo samples that are then routed to four mono outputs which are placed around the scene.