Soundtracks can include plenty of different elements and you’d normally build them up in layers, with different varieties of sound on different tracks.
Most films also use sound that we all know has been added: things like voiceovers, and background music. this is often called non-diegetic sound.
You can use music to line the scene and show where and when the film is ready. So a scene of an old house becomes France if you play accordion music, or the 18th century if you hear baroque music.
You can also use it to determine the mood, or change it. Deep, sinister tones tell us that something scary is on the point of happen, or that a personality who seems friendly is truly dangerous. High violin notes suggest tension, and discordant sounds make us feel uncomfortable. Fast music can add excitement to an action scene.
Hits are where the music exactly matches an action we see on the screen, though if you employ them an excessive amount ofit’s cheesy: it’s called ‘Mickey Mousing’ because it’s commonest in cartoons.
You can also use music that goes against what you see on screen. to makea way of irony, use happy music for a tragic or scary scene. this is often sometimes called contrapuntal music (as against parallel music, which matches what happens on screen.)
In a longer film, you’ll even give each character their own air or leitmotif.
Sound and editing can work together. Changing the sound and therefore the image at different times (split edits) can make a sequence flow more smoothly, because it makes the cuts less obvious. otherwise you can link two scenes employing a sound bridge. So at the top of a scene in an office we’d hear birdsong, before we movethe subsequent scene which is within the woods. This helps prepare us for the change of scene.
You can also edit your whole film or sequence to music, with the pictures changing on every bar, every beat, or when there’s a change within the mood of the music.
Don’t forget the ability of silence. A sudden change from hectic music to silence will be shocking, and some seconds of silence during a dialogue scene can build up anticipation and tension. You don’t usually want complete silence: the essential background ‘ambience’ of the placement should usually persevere.
Media studies blog 