We watched two different opening shots for “Touch of Evil”. Both contained audio for theme music and street noise, and you can’t have one without the other. Take out the theme music, and you’re left guessing the mood and tone of the scene, and possibly the whole movie. The theme music, and the soundtrack for the rest of the movie, is created to convey a specific emotion or “sense” (sense of danger, calm, energy, etc.). The music communicates what the director is attempting to arouse in you, and he/she can manipulate those feelings to create a mood, be that irony, suspense, or what have you. But it needs to compliment the “street noise”, or the realistic scenery noises, aka background noise. Background noise is very important to the scene. If you take it out, you’re left with Charlie Chaplain films from the 1920’s
Now, there’s nothing wrong with silent films. They can be very fun and entertaining, but it’s extremely limited in what you can do artistically. Background noise takes the scene from 2-D to 3-D, making the situations of the actors more relatable.
Comparatively, theme music is vastly more important then street noise. Even Plays (not including sketches) at least have intro pieces, and sometimes even theme music for certain characters. But street noise is like the altos in a choir (please bear with this metaphor), and the music is the Sopranos. Sopranos are the melody that get your point across, but the Altos make the choir enjoyable and stand out, and are absolutely necessary to make a chord.