This paper discusses the design of audio games, a quite new computer game category that originates from games for players with visual impairments as well as from mainstream music games. In the TiM project (Tactile Interactive Multimedia), SITREC develops three sound-based games that point out new directions for game audio design. The TiM games demonstrate different ways in which games can be designed around an auditory experience. Several unique features of audio games are presented emphasising unexplored potentials for interactivity and future development areas are suggested. SITREC proposes an approach to the design of auditory interfaces that takes three listening modes into consideration: casual listening, semantic listening and reduced listening. A semiotic model is presented that illustrates this view on sound object design and ways in which sounds can be combined. The discourse focuses on issues of continuous display, musicality and clarity, and introduces the notion of "spatialised game soundtracks," as opposed to separated background music and game effect sounds. The main challenge when developing auditory interfaces is to balance functionality and aesthetics. Other important issues are the inclusion of meta-level information in order to achieve a high level of complexity and to provide elements of open-endedness. This refers to planning the overall gameplay, as well as to designing individual sound objects and combining them into complex, interactive soundscapes.