Sound Propagation or “the sounds living in the space”, a term frecuently used in Sound Design. Let’s see these two articles taken from two blogs (Interactive Sound and Sound&Music for Games), both talking about Sound Propagation in Games.
“Sound propagation is a term used to describe how sound reacts to a given space. We know that sound travels through the air as a linear wave, the wave forces the air molecules to vibrate allowing the sound to travel. Sound propagation is not simply the reduction in volume as a listener moves away from a sound, it relates to the way the sound reflects and diffracts off certain surfaces. In terms of games, replicating the propagation of sound accurately is important, as it adds to the overall impression of ‘realism’ that the game creates.”
The volume of a sound will obviously reduce as the listener moves further from it, and vice versa. The volume of the sound source will not react in a linear fashion, for a given radius the volume of the sound will react in a logarithmmic fashion. For instance as you can see in the rough graph i have made below, as the player/Listener moves slightly from the source there will be a very slight reduction in the volume of the sound, as the player reaches a certain point the sound will tail off very quickly. This happens as the energy of the sound wave dissipates and in simple terms cannot force the vibration of the air molecules any more.
The propagation of a sound mainly refers to how it is reflected, refracted and attenuated by the environment and the objects around it. These elements of propagation affect the characteristics of a sound and the better we can emulate these elements of propagation in computer games, the more realistic and immersive the games will become.
This diagram (from here) gives a basic illustration of the phenomena involved with sound wave propagation.