Minecraft wiki entry for Ambience, associated text: Mood ambience sounds occur based on a "mood" percent value between 0–100. The mood increases when the player is in a cave or in a dark place, and decreases otherwise. When the mood reaches 100%, one of the sounds plays randomly, resetting the mood to 0% and thus restarting the cycle. The darker it is, and the more non-transparent blocks there are, the quicker the mood increases. in Java Edition, the current mood value appears on the debug screen.