It must retain its own line. By this he maintains that in addition to the moving rhythmic feel suggested by a succession of pictures, there must exist a distinct rhythm and motion implied by the music itself. To Pudovkin the quality of sound is an essential part of the film making process. Though different in certain aspects, they expand greatly on many of the theories set forth by Pudovkin. In fact, Zettl credits Pudovkin with many ideas in his book.
Literal sound is referential sound .
The sound itself is less important than what it stands for. We are oriented in time if we can readily associate the literal sounds with a time period , such as morning, evening, night. Nonliteral sound has no literal meaning. It is not symbolic, which means that it does not stand for a particular thing or event. The most common nonliteral sound is music.