In most analyses, how film music is used is divided into two categories: diegetic and non-diegetic. Diegetic music is understood to emanate from a source in the fictional narrative or “diegesis”. Hence it is also known as “source music”. These sources may include a radio, stereo, speakers, live musicians, and so on. Whether or not we see the source is unimportant. So long as we understand the music to be coming from something in the film itself, it qualifies as diegetic music. Thus, the characters in the film are able to hear this music. The cantina scene in the original Star Wars is an example of diegetic music.
Conversely, non-diegetic music is understood not to emanate from the film itself, so the characters do not hear it. Other names for this type of music include “underscore”, “accompanimental music”, “commentary music”, “interpolated music”, and perhaps most commonly, “background music”. Most film music is non-diegetic music, one of the most familiar instances being the music for the shower scene in Psycho.
The distinction between diegetic and non-diegetic music forms an important part of how film music is made because they generally have markedly different functions. Diegetic music is usually used to clarify time and place, social circle, or nationality. The frequent use of this type of music in the Godfather films helps to paint a convincing picture of Italian culture, particularly through Italian folk song and Italian opera. The wedding sequence in the first film is one example among many:
Non-diegetic music, which is far more common in film, typically reflects the psychological state of the characters onscreen, or suggests how we ought to emotionally interpret the images we see. Because this type of music especially helps us to immerse ourselves in the film’s fictional world, it tends to be a more prominent part of films in the genres of action and fantasy, where the suspension of our disbelief is especially crucial. Hence the lavish scores of such film series as Star Wars and The Lord of the Rings.
A Third Category: Source Scoring
While the difference between diegetic and non-diegetic music is clear, some film music cannot be described as entirely one or the other. In his book, Scoring for Films, Earle Hagen argues for a third category of film music he calls source scoring, a combination of source music and dramatic scoring (or non-diegetic music):
This kind of music is like source in its content, but tailored to meet scoring requirements. … This kind of cue can start as pure source music and change over to source scoring. … The main difference between Source and Source Scoring is that source scoring takes on a much closer relationship to the film. It follows the framework of the scene more critically and matches the nuances of the scene musically.
A few examples will demonstrate how this kind of music operates in film.
Example 1: The Man Who Knew Too Much
In Hitchcock’s The Man Who Knew Too Much (1956), the final concert scene involves a performance of Arthur Benjamin’s “Storm Clouds Cantata”, which clearly begins as diegetic music. In this clip, the cantata starts at 0:17 (by the way, that’s the film’s composer, Bernard Herrmann, conducting):
But as tension mounts, so does the music. And instead of non-diegetic music coming in overtop of the cantata, the cantata itself acts as non-diegetic music in that it seems to comment on the scene. When Ben (James Stewart) arrives at the concert hall in order to prevent the murder of the Prime Minister, he is obviously distressed. It is at this point that the cantata begins its noticeably more active second half. But it is also here that the orchestra stops being shown for a few minutes while Ben tries to find the assassin. The character of this music matches Ben’s emotional state so well that it starts to sound just like non-diegetic music. And interestingly, there is no dialogue through this part of the scene. Indeed, as Royal S. Brown notes in his book, Overtones and Undertones, it is almost “as if it had come straight out of the silent era.”
At the same time, we are of course aware that this is actually the cantata being performed, so both the diegetic and non-diegetic realms merge. This, then, is a perfect example of source scoring. Watch the above clip from 5:45 to see how the use of the music changes when Ben enters. Notice how many of the characters’ actions are choreographed to the music—for example, when Ben reaches his wife Jo (Doris Day) at 6:01, the music suddenly begins a new phrase, as though to articulate the moment as important. The same thing happens when Ben leaves Jo to look for the assassin at 6:16.
Example 2: The Adventures of Robin Hood
In The Adventures of Robin Hood (1938), Prince John attempts to set a trap to capture Robin by holding an archery tournament. For the start of this scene, Erich Korngold wrote a rousing fanfare for trumpets, and we actually see the trumpeters play the beginning of this music. We also hear a snare drum, but it is not difficult to imagine a drummer just offscreen somewhere. So at this point, the music seems clearly diegetic. But with the cut away from the trumpeters, the music suddenly becomes more richly scored, adding strings, French horns, and cymbals, and so, lacking any source onscreen, suggests it has now become non-diegetic. Compare these moments in the following audio clip starting from 6:00:
Korngold’s score for the film is entirely orchestral, and despite being presented as diegetic music, the opening fanfare in this scene retains that orchestral feel. The sound quality of the fanfare has exactly the same “studio sound” as the richer music that follows, and the fanfare ends with a timpani “thud” that again suggests the unseen orchestra of a non-diegetic score. Thus it seems that non-diegetic music is being treated as diegetic music. Why not just leave it as non-diegetic music? With the addition of trumpeters to ground the music in the diegetic world, the scene is made to feel more authentic, as is the case with most diegetic music. This is the opposite situation of The Man Who Knew Too Much, where the music in the concert hall scene was always diegetic, but sometimes acted non-diegetically as well. Both scenes, however, are examples of source scoring.
Example 3: American Graffiti
Source scoring does not only work with orchestral music. In American Graffiti (1973), the music is a virtually continuous series of popular songs from the 1950s and 60s. Because these songs are almost always understood to be coming from a source in the film’s fictional world (usually a car radio), they qualify as diegetic music. And their function would therefore seem to be clear: to re-create the sound world typical of American adolescents during the early 60s. But the way in which the songs, and particularly the song titles, merge with the images and dialogue suggests that they go further than this.
Consider some of the scenes with John (Paul Le Mat) and Carol (Mackenzie Phillips). John initially asks a carload of girls whether any of them wants to ride with him in his car. The only volunteer is Carol, the younger sister of one of the girls. Feeling that she is too young for him, John is contemptuous of Carol and embarrassed to be seen with her. When Carol first gets into John’s car, the song playing is Buddy Holly’s “That’ll Be the Day”. As Peter Larsen observes in his book, Film Music, the song is initially commenting on John’s request to the carload of girls to consider “going steady” with him. But as the scene progresses, it appears to become an ironic commentary on John and Carol’s relationship. In other words, “That’ll Be the Day” seems the perfect way to describe any possible romance between the two. View the scene here (“That’ll Be the Day” enters at about 1:20):
Later on at the drive-in diner, John becomes embarrassed at being seen with Carol by a friend. John introduces Carol as his cousin, whom he says he is “babysitting”. Carol becomes upset and leaves the car to wander the streets alone. John, obviously harboring some feelings for Carol, goes to pick her up when he sees her being taunted by some other male teens. All the while, we hear The Monotones’ hit song, “The Book of Love”. The song seems to suggest the budding romance between John and Carol despite John’s attempts to pretend otherwise. View this scene below:
In a later scene, John encounters another car full of girls, one of whom throws a water balloon at John. The balloon instead hits Carol in the face and as retaliation, John and Carol deface the girls’ car with shaving cream and flatten one of their tires at the next stop light. The song we hear during all this is Chuck Berry’s “Johnny B. Goode”, which again seems an ironic commentary on the pranks the teens pull on each other. Watch the scene here:
Although most analyses regard film music as either diegetic or non-diegetic, there are times when a combination of the two is at work. When this occurs, the music can be viewed as source scoring. While blurring the boundaries between diegetic and non-diegetic music may seem undesirable, it allows the music to perform the functions of both types of music without changing anything about the music itself. Thus, source scoring is useful in creating a particularly smooth flow in the film experience, as is certainly the case with the examples above.