Via Starwars.com:
IN-UNIVERSE STAR WARS TUNES ARE A MAJOR, IF SUBTLE, STORYTELLING COMPONENT OF THE SAGA. PLUS, SONGS LIKE “JABBA FLOW” ARE JUST REALLY FUN.

Music is a very important part of the Star Wars experience, but the way that the saga plays with sound is particularly intriguing to study. Straddling the fence between score and sound effects is source music. Source music is also sometimes called “diegetic music,” meaning that it comes from a source in the story like a speaker in a car or a live band. Non-diegetic music would be something that the characters inside the story can’t hear, like their own themes and dramatic underscoring.

Even from his early days in film school, George Lucas was fascinated by sound effects. From the disembodied electronic chatter and strange distorted dialogue in his world-famous student film Electronic Labyrinth THX 1138 4EB, source sounds become an effective tool in Lucas’s world-building tool kit.

An extension of this technique is source music, and American Graffiti exemplifies the use of source music. Without the common thread of Wolfman Jack’s radio station blaring throughout the film from radios and cars around town, there is no movie. The highly memorable assembly of songs in Graffiti helped the soundtrack album secure triple-platinum status. So inextricably linked are the songs and the story that George Lucas reportedly conceived of each scene with a particular song in mind.

Generally, source music is treated much more like a sound effect. The saga’s first source music, heard in the Mos Eisley cantina in A New Hope, is a perfect example. Not only does the music change channels from left to right to sound like it’s coming from the same place in every shot, but you also get the crowd reacting to the music, with the cantina patrons reacting when the band plays a new song. In Rogue One, the latest Star Wars film, source music is heard low in the mix during the Jedha street sequences, adding to the busy feel of the depressed, Empire-occupied world.

If you can’t put your finger on some instances of source music in the saga, here’s a mostly-complete list of the memorable tracks from within the Star Wars universe.

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