Just yesterday I watched Richard Linklater's Boyhood (production 2001-13; released 2014). The film, which has won many awards, is remarkable in that it follows the same set of actors as characters through a twelve-year period, focusing the narrative on two children, their mother, and her husbands. At 2 hours and 45 minutes, it is long but by no means excessively so by today's standards, though to some viewers (like this one) it may feel even longer because—except for abusive outbursts by the second and third husbands—it is low-key dramatically and emotionally throughout. But those viewers (like this one) will certainly also acknowledge that the film's point is a true-to-life coming-of-age story and that "low-key" is not only appropriate but desirable.
Also appropriately, given the genre, film editing and sound editing are both traditional and non-intrusive. That brings me to the topic of this post. Diegetic music is heard several times in different environments—family singing, a band, etc.—but the music is so wholly embedded in and so thoroughly motivated by the narrative, that by film's end it remains in the memory at about the same level as image backgrounds of suburban houses in Houston, Austin, and San Marcos, Texas, the film's three locales. At least that was the case for viewers like this one. . . . I suspect the fact that no particular music acts as a sound motif contributed to this assessment.
In the early Hollywood sound film, especially dramas and action films, a similar effect could be created, inadvertently, by the nondiegetic orchestral scores that routinely played through at least 50% of the film's run-time—and often more than that. Through its sheer abundance—in some studios abetted by low volume levels—such "wall-to-wall" music could often be tuned out, one basis of Claudia Gorbman's term "unheard melodies." That was the case even for viewers like this one, whose primary research interests were in early Hollywood sound film.
There is of course no conceivable objective measurement for attention to music in the soundtrack. In Hearing the Movies, our central goal is to add skills of critical listening to skills of critical viewing, but we also admit the unwanted potential to distort one's viewing practice. That is to say, in recollection and interpretation of a feature film, it is always good to stand back and consider music in the context of the film's overall narrative, design, and effects.