I picked the “1.21 Gigawatts” scene from “Back to the Future”. In this scene Marty is showing Doc a video shot before Marty had accidentally went back in time to the 1950s. In the scene, Marty is showing 1950s Doc what 1980s Doc had done in order for him to time travel. 1950s Doc tells Marty that he can’t help him because he cannot generate that much power, until it comes to Martys attention that they could somehow orchestrate a plan to have the time machine (the DeLorean) get hit by lightening and send it back to 1985. The movie as a whole follows Marty going back in time and running into the younger versions of his parents. This leads to him needing make them fall back together, as the younger version of his mother begins to pay more attention to Marty than the younger version of his father.
Some diegetic sounds in the scene include the audio from the tape Marty plays, the sound of the tape rewinding, the sound of Doc hitting the garage door, and the sound of the paper Marty shows Doc. Some nondiegetic sounds include the sound of an instrument (either a trombone or clarinet, I can’t tell) when Marty figures out how to get back to 1985 and all the other instruments that start playing (violins, flutes, trumpets) as the scene progresses. The scene for the most part stays silent other than the diegetic sounds throughout it. It isn’t until the “climax” or “breaking point” in this scene when Marty and Doc figure out a plan that the music begins. The music adds a level of anticipation, as they unfold the plan even more, the speed of the music increases. As the tempo increases, so does the excitement and anticipation of the scene.