con sordino explained
A direction to play with a mute, creating a softer, more veiled tone quality
In Depth
Con sordino (with mute) appears as a performance instruction in string, brass, and occasionally percussion parts. For strings, a small clip-on mute dampens the bridge vibrations; for brass, a mute is inserted into the bell. The resulting tone is not merely quieter but fundamentally different in colour — warmer, more distant, and more intimate. The companion instruction senza sordino (without mute) directs the player to remove the mute. Mute changes require several seconds, which composers must allow for.
Beethoven's Moonlight Sonata is marked senza sordino (without dampers), meaning the sustain pedal should be held throughout — creating the shimmering haze of sound.