1. Understanding the purpose of diegetic and non-diegetic sound

Diegetic sound

Diegetic sound is sound that can be heard from the characters in a film or a tv show and can be heard from the audience watching it. It can be on or off screen as long as it has score or object coming out of it.

For example,  one scene in the Si-Fi film EX Machina, the Main protagonist dances with the robot while the song "Get down Saturday night" plays in the background to try and communicate with the robot. The use of the diegetic sound is effective because to try and show the audience that the robot has some emotion. She is dancing to the music to try and humanize her.

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Another example is a scene from The house of the devil where the main protagonist walks round a house dancing while listening music. This use of diegetic sound is used to the upbeat personality of the main protagonist which is junkstaposed my the seemingly dark and depressing house she's living in.

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Non- diegetic sound

Non- diegetic sound is sound witch is neither visible to the character in the movie or on screen. for example a use of non- diegetic sound could be and original movie score or any songs wherethe character can't hear but we can.

For example, in the opening of The Shining, the use of non- diegetic sound in the opening scene is very unsettling and scary so that it can pre pare the audience for coming scary while the main protagonists don't know what they are getting themselves into.

Another example is the opening to Forest Gump where the Opening theme is play to show tell the audience that this is going to be a light hearted and emotional story through calm and almost emotional  music.