The stapedius is the smallest skeletal muscle in the human body. The stapedius dampens the vibrations of the stapes by pulling on the neck of that bone. This helps to control the amplitude of sound waves from the general external environment to the inner ear. This protects the inner ear from high noise levels, primarily the volume of your own voice. Recordings of your voice sound odd because the stapedius muscle isn’t functioning then.

Source: https://en.wikipedia.org/wiki/Stapedius_muscle#Function