One of the hardest things that many filmmakers grapple with is what to do with music during dialogue. A good argument can be made that dialogue needn’t have much music. However, to the extent that there are important plot points during a dramatic or comedic film, or important emphasis points in a corporate or promotional film, that happen during dialogue or narration, the filmmaker is missing out on the opportunity of highlighting these important moments for their audience and moving their story to the next phase.
When we talk about “density” in audio we mean how much aural or sonic space a dialogue track, sound effect, musical instrument, orchestra, etc., takes up in the available aural space. This is not volume (loudness) but represents the sonic “thickness” taken by that item. Some sounds are denser than others.
"Spotting" is a technique used by professionals in film and television wherein certain key creative people involved in the project, typically the producer, director, editor and composer, review the film or show, scene by scene and determine not only where music should begin and end in each scene (to the frame), but also what it should evoke, emote or communicate to the audience and even how much music the project should have in general.