Realistic, Expressive, and Surreal Sound Examples

Film Element: Realistic Sound (Diegetic) (Character)
Realistic sound, also known as diegetic sound, is sound that would logically exist in the audio world depicted on the screen.  In the critically acclaimed Klute, diegetic sound is cleverly used to reveal character.

Film Example: Klute: In the filmed version, Jane Fonda is seated across from the antagonist.  The antagonist forces her to listen to an audiotape he has brought with him.  As the tape progresses, Fonda realizes she is listening to her friend's murder.  When Fonda looks over at the man, she sees that he is completely unmoved by the woman's screams.  At that moment, Fonda realizes that the tape is serving as foreplay to murder - and that she is the next victim.
Dramatic Value: The antagonist's lack of response to a sound is used to reveal character. Suspense is created as we watch the protagonist decode the antagonist's response.  The turning point occurs when the protagonist succeeds, prompting a new action.

Film Element: Realistic Sound (Diegetic) (Emotional Response)
Different sounds evoke different emotional responses.  The sound of knocking on wood is generally positive, the sound of metal against metal, negative.

Dramatic Value: By giving the antagonists a sound tag, the audience can judge how close they are to their victim, whether they are closing in or losing ground, regardless if they appear on screen or not.  This forces the audience to participate, mimicking the action of the victim, in carefully listening to sound clues so they can quantify what distance lies between the antagonist and the hero.  In this way sound can encourage a heightened level of audience participation as well as raising suspense.

Film Element: Expressive Sound (Diegetic) (Outer World)
Expressive diegetic sound that is organic to the scene but has been altered for dramatic effect.

Dramatic Value: By using simple sound cues expressively, the directors make use fear for the protagonist.  By connecting the sound cues along with other clues, the audience starts extrapolating.  We wonder what "bad things" await.

Film Element: Surreal Sound (Meta-Diegetic) (Inner World)
Meta-Diegetic is any sound that represents a character's inner world, such as nightmares, dreams, hallucinations, wishes, and so on.

Dramatic Value: Barton Fink: Once you cross the threshold and accept that sound does not need to be rooted in reality, that sound can be pulled from anywhere in expressing a character's thoughts, a huge creative door opens. Sound and picture do not need to match - in fact it is the mismatch that gives the scene heightened interest by suggesting we are hearing the character's inner thoughts.