The film Melody is an educational Adventure in Music animated short 
produced by Walt Disney Productions, and released to theaters by
RKO Radio Pictures. It was the first cartoon filmed in 3D and was the
first in a proposed series of shorts teaching the principles of music. 

The 3D process never really caught on with theater audiences because
of the need to wear the polarized glasses, but the cartoon remained a
novelty at Disneyland for several years.

Professor Owl teaching musical principles to his class.