Audio Maps

Abstract: In most modern computer games, ambient soundtracks are used to enhance the immersive quality of the game. These ambient tracks are often simply stereo samples playing on repeat for as long as the player's avatar is within a simply specified – for example, within a given distance – area in the game world. This kind of ambient sound provides only the crudest form of navigational information – whether the player avatar is inside or outside the ambient source's area of effect. This thesis discusses the idea and implementation of a system that allows for arbitrarily shaped areas of effect by using painted maps. The source fields are generated from the maps in order to emulate directionality and distribution of the ambient sound. In addition, the implementation should also take the height map of the game terrain into account, and change the behaviour of the source fields accordingly. The implementation uses the OpenAL interface to position point audio sources, according to the calculations based on the input maps, for the audio output. Two different approaches to point source positioning were examined; the grid layout, where the point sources were positioned uniformly around the avatar, and the dynamic sector approach, in which the positioning depends on how big a circle sector the source field describes as seen from the avatar position. The terrain interaction uses a ray-tracing algorithm that “crawls” over the landscape to find the shortest possible straight path from avatar to source over the terrain. In the current version of the implementation, a simple intensity modification accounts for the terrain impact on sound propagation.