Sound is a vital part of the information used for decoding film - whether it comes in from of a string soundtrack or footsteps echoing down a corridor.

· This may be diegetic (coming from inside the narrative world of the film) or non-diegetic (coming from another source).

· It can be further divided into dialogue (human voices), synchronous (matching actions seen on the images) or asynchronous(from unseen sources) sound effects, and music.

The extra dimension that sound adds to film has been acknowledged since the early days of cinema, when live music in the form of a piano, organ or even a full orchestra accompanied the images on the silent cinema screen.

In 1927 Warner Bros. released the first film with a soundtrack - 'The Jazz Singer' starring Al Jolson. The next commercial sound film 'Lights of New York' (1928) was so impressive that it stimulated a rapid and total conversion to sound within the entire film industry.