This thesis concerns itself with a phenomenon found in film music that can be described as audible diegetic transitions. In short, an audible diegetic transition occurs when film music shifts from one implied musical placement to another by changing its pre­sented sound quality. This occurs predominantly through the employment of music that is pre-existing in relation to the release of the film where the music is utilised. These audible diegetic transitions are categorised as aural displacements and transaural dis­placements which are both anchored in previous re­search concerning stable musical place­ments. In order to answer the research questions regarding technical aspects and narra­tological implications, the thesis is centred around a film music analysis. The de­marcation of said analysis uses pre-existing songs from the film Joker (Philips, 2019) as its main focus. In order to provide a colourful and meaningful discussion the selected material also contains a variety of examples from other films. The analysis shows that the selected audible diegetic transitions can provide narra­tological implications both for a film as a whole and for a specific scene or se­quence in any film. In Joker specifically, the audible diegetic transitions arguably contain the narra­to­logi­cal im­plication of adding to the retrospective and unreliable narration, which is im­port­ant for the story of the film. The thesis also argues that the technical aspects of the ana­lysed audible diegetic transitions can be condensed into being either diegetic to comm­en­tary, or vice versa. Diegetic music is, in this context, defined as music that is im­­­­plied as being heard in the acoustic space of the story-world, whereas commen­tary music is an um­brella term defined as music that is not implied being heard in the acous­tic space of the story-world. The analysis shows that these transitions can transpire either instantly or gra­­­dually with the change of sound quality from being either narrow or wide. These tech­nical aspects contribute in under­standing the narratological im­plications of said au­dible diegetic transition by categorising them as either emotive or groun­ding. Both of these narratological implications can be concluded and described as swift enforcers of the relationship be­tween the one consuming the film and the char­acters, or lo­cations, of the film they are con­­­­suming. Audible diegetic transitions figura­tively breach the fourth wall that is the screen.