Sound film
The primary steps in the commercialization of sound cinema were taken in the mid- to late 1920s. At first, the sound films which included synchronized dialogue, known as "talking pictures", or "talkies", were exclusively shorts. The earliest feature-length movies with recorded sound included only music and effects. The first feature film originally presented as a talkie was "The Jazz Singer", released in October 1927. A major hit, it was made with Vitaphone, which was at the time the leading brand of sound-on-disc technology. Sound-on-film, however, would soon become the standard for talking pictures.
M (1931 film)
"M" was Lang's first sound film and Lang experimented with the new technology. It has a dense and complex soundtrack, as opposed to the more theatrical "talkies" being released at the time. The soundtrack includes a narrator, sounds occurring off-camera, sounds motivating action and suspenseful moments of silence before sudden noise. Lang was also able to make fewer cuts in the film's editing, since sound effects could now be used to inform the narrative.