Tail off
Definition 1 of 2
Pro Tip 1/3Sensory Fading
Used when senses like sound or sight gradually reduce in strength. 
The echo of the sirens tailed off in the distance.
Pro Tip 2/3Interest Decline
Refers to slowly losing interest or attention over time. 
As the lecture dragged on, students' attention began to tail off.
Pro Tip 3/3Emotional Cooling
Describes emotions decreasing in intensity, such as excitement or anger. 
His initial anger tailed off once he understood the situation.