The terms are used in film theory to separate elements that can be said to be part of the depicted fictional world [diegetic] from elements that the fictional characters cannot see or hear [non-diegetic] and which should be considered non-existent in the fictional world (Bordwell, 1986; Bordwell & Thompson, 1997)
Jørgensen argues to reflect on the terms.
Two concepts from narrative theory that often appears in discussions about game sound are diegetic and non-diegetic (Collins, 2007, 2008; Ekman 2005; Grimshaw 2008; Grimshaw & Schott 2007; Jørgensen 2007b, 2008; Stockburger, 2003; Whalen, 2004). The terms are used in film theory to separate elements that can be said to be part of the depicted fictional world from elements that the fictional characters cannot see or hear and which should be considered non-existent in the fictional world (Bordwell, 1986; Bordwell & Thompson, 1997). According to this approach, dialogue between two characters is seen as diegetic, while background score music is seen as non-diegetic. In connection with game sound, a likely adaptation of these concepts would describe the response “More work?” from an orc peon unit in the real-time strategy game Warcraft 3 (Blizzard, 2002) as an example of a diegetic sound since it is spoken by a character within the gameworld. Music that signals approaching enemies in the role-playing game Dragon Age: Origins (Bioware, 2009) would according to this view be an example of non-diegetic sound since the music is not being played from a source within the game universe.
However, when analyzing the examples more closely, we see that using these terms in computer games is confusing and at best inaccurate. As a response to a player command, the “More work?” question has an ambiguous status in relation to the gameworld: If we ask ourselves who the peon is talking to, it appears to address the player, who is not represented as a character in the gameworld, but manages the troops and base from the outside of the gameworld. The warning music heard in the role-playing game is also ambiguous. Although there is nothing to suggest that the music is being played by an orchestra in the wilderness, there is no doubt that the music influences the players’ tactical decisions and therefore has direct consequence for the player-characters’ actions and the progression of the game. The confusion comes into being because game sound has a double status in which it provides usability information to the player at the same time as it has been stylized to fit the depicted fictional world. It works as support for gameplay, while also providing a sense of presence in the gameworld (Jørgensen, 2007a, 2009; Nacke & Grimshaw, 2011). From this point of view, diegetic and non-diegetic sounds tend to blend systematically in games, thereby creating additional levels of communication compared to the traditional diegetic versus non-diegetic divide.
Jørgensen, K. (2011). Time for New Terminology?: Diegetic and Non-Diegetic Sounds in Computer Games Revisited. In M. Grimshaw (Ed.), Game Sound Technology and Player Interaction: Concepts and Developments (pp. 78-97). IGI Global. https://doi.org/10.4018/978-1-61692-828-5.ch005