Sound theory

Sound: Sound is the way in which sound is used to communicate meaning. The manipulation and layering of sound to create meaning. Sound can be a complicated feature of film studies, unless deconstructed and certain terms applied can pass you by and not seem important.

Diegetic sound: Any voice, musical passage, or sound effect presented as originating from a source within the film's world is diegetic.

Non-diegetic sound: If it originates outside the film (as most background music) then it is non-diegetic sound. Non-diegetic sound is sound that the characters in the film can't hear but the audience can.

Voiceover: When a voice, often that of a character in the film, is heard while we see an image of a space and time in which that character is not present in. The voice over is often used to give a sense of a character's subjectivity or to narrate an ever told in a flashback. 

Sound bridge: Sound bridges can lead in or out of a scene. They can occur at the beginning of a scene when the sound from the previous scene carries over briefly before the sound from the new scene begins.  Alternatively, they can occur at the end of a scene , when the sound from the next scene is heard before the images appear on screen. Sound bridges are one of the most common transitions in the continuity editing style, one that stresses the connection between both scenes since their mood (suggested by the music) is still the same. 

Pleonastic sound: Pleonastic sound is sound that is exaggerated, e.g. the sound of lightsabers slashing the air in Star Wars, or  a tap dripping more loudly than usual in a horror film. It is used to create fear, tension, excitement etc.

(example of pleonastic sound in Star Wars) 

Contrapuntal sound: Sound that doesn't easily match the images that they are accompanying, or even run against them. This can have a quite disorientating effect upon the audience and make them question what they are seeing.  

I have chosen the scene of Gwen Stacy's death from The Amazing Spider-Man 2 to show how the aforementioned key terms are used in film.

In this scene we see Gwen Stacy (Emma Stone) falling within the clock tower, and we can hear the music as well as the sound of the gears in the clock tower falling simultaneously. We also hear the sound of Spider-Man's web that he springs to save her. The music score helps to create a sense of tension in the scene as the audience is unaware if Gwen will be spared from her death and be saved but as we see her fall, and hear the snap of her neck, the audience knows that she did not survive the whiplash of the fall.