How William uses sounds in the play?

In Streetcar, stage effects are used to represent Blanche's decent into madness. The maddening polka music, jungle sound effects, and strange shadows help to represent the world as Blanche experiences it. Consider the stage direction,

“Polka music sounds, in a minor key, faint with distance.”

THe music stops and starts according to how Blanche recalls episodes in her life like her husband's suicide. She recalls the homoeroticism which is matched by the music. There is also a cool Jazz sound to the play which is a prelude to Blanche's grand entrance.