Diegetic and Non-diegetic Sound

Diegetic sound

       Diegetic sound is sound that exists within the filmic world (the diegesis), but not necessarily in the shot. This includes: voices from characters on the set, sound made from objects/ interactions (e.g. a chair) and sounds made off screen from other characters or elements. So even if I can't see a particular action happening on screen (e.g. a person clapping) the sound made is still diegetic, because it exists within the reality of the film.
       In the film 'When Harry Met Sally' there is a scene in which Harry and Sally are sat across from each other in a cafe talking. Their voices are an example of diegetic sound, as well as the voices of the extras, even though they're not in the shot. Without the diagetic sound in that scene it would seem very unrealistic, because when is a cafe ever completely empty and silent?
       In the following clip (http://www.youtube.com/watch?v=wcjY-VN8_l4) from the film  'Taken' uses diegetic sound to amplify the emotions of the character and the audience. Because you can hear things smashing and screaming, it's clear that Sam is being kidnapped even though we can't see it happening. The use of this makes us feel as helpless as her father whose listening to this happen through the phone. These diegetic sounds also build tension for when the father speaks to the kidnapper through the phone. If I wanted to create a dramatic effect in one of my projects I would consider using diegetic sound to tell the audience what's happening off screen, because the uncertainty would put the audience on edge.

Non-diegetic sound

       Non-diegetic sound is sound that is added into the film in post production to enhance the mood of the film. This includes: music that is added in the editing process (the score) and any sound added in post production like a narrator's commentary (like a character's thought track). An example of non-diegetic sound is a wild track, which is background noise (e.g. from a party) that is used for multiple shots or a scene.
       In the film 'Kick-Ass' the main character narrates the beginning of the film to catch the audience up on what the film is about. WIthout this narration, the audience would be very confused as to the topic of the film and the motivation of the character, making this non-diegetic sound very important. Also, the director used an adapted version of the soundtrack called "Surface of the Sun" to bring an epic feel to the "Hit Girl rescues Big Daddy" scene. The long violin notes amplify the emotions of the audience, making the scene more emotional. The music also matches the slow motion used in the scene.
       In the following clip (http://www.youtube.com/watch?v=USHi4s_rHqQ) from the film 'Wreck it Ralph' the use of a non-diegetic soundtrack amplifies the emotions of the situation. Without the swelling music to accompany Ralph destroying Vanellope the audience wouldn't recognise Vanellope's anguish as well. The music is also in time with her screaming as Ralph destroys her cart, so the mixture of diegetic and non-diegetic is very effective. I could use this technique in one of my future projects, as it would engage the audience in the video and allow them to empathise and identify with the characters. I've always found that the non-diegetic soundtrack is what makes an emotional scene emotional.

Juxtapositions

       Using a mixture of diegetic and non-diegetic sound can create a juxtaposition. A juxtaposition is when two or more different things are paired to create a comic or scary effect. For example, happy music paired with a scene of someone getting murdered and screaming.
       There is a scene in the film 'The Funny Games' that consists of an upper class German family driving to their holiday home. At first they are listening to classical music, but then heavy metal replaces it. The use of this juxtaposition gives the audience a clue as to what's going to happen to the unsuspecting family.
       In the final scenes of The Godfather 3 you see the family attending a baptism service which is accompanied by calm music. Through parallel editing you can see several murders happening at the same time in a different location, but the same calm/ happy music is played over these. This is a juxtaposition as getting murdered isn't a calm or happy experience, it's quite the opposite. I would use this technique in my own work to make certain scenes funny, ironic or foreshadowing, depending on the nature of the project.

Mood and meaning

       Without a non-diegetic soundtrack, certain scenes would lose their mood and meaning. For instance, if the following scene (http://www.youtube.com/watch?v=2JfjO1PZxXc) from 'Kick Ass' didn't have the non-diegetic soundtrack it wouldn't be perceived as funny, it'd be perceived as a serious action sequence. The pop/punk music reflects Hit Girl's personality as well, giving the audience a further understanding of her. In my projects I would make sure that the scenes that require a non-diegetic soundtrack have the appropriate music to amplify the audience's emotions.