Theodore Case Sound Test: Gus Visser and his Singing Duck, also known as Gus Visser and His Singing Duck, is a 1925 American short musical comedy film starring vaudeville performer Gus Visser. The short is an early sound film, directed by Theodore Case while perfecting his variable density sound-on-film process. Case began working on his sound film process at the Case Research Lab in Auburn, New York, in 1921.