More Internet Movie Archive films to check out:

[BradOlson]

http://www.archive.org/movies/movieslisting-browse.php?collection=prelinger&cat=Motion%20pictures:%20Sound

This link is a link to 2 films about sound recording in motion pictures.

http://www.archive.org/movies/details-db.php?collection=prelinger&collectionid=07864 has an insiders view of a 1930s radio studio producing sound effects.

[BradOlson]

http://www.archive.org/movies/details-db.php?collection=prelinger&collectionid=fndvoce has a cartoon on how sound motion pictures work.