Sound Propagation in Games

'Sound Propagation' in games, is the term given to a system built into the game that allows for sound to be manipulated in relation to the environment. One of the benefits of realistic sound propagation in a game is that it can dramatically increase immersion of the player. The sound propagation's wave interaction effects the following:

Reflection - Absorption - Diffraction- Refraction

Sound reflection is a one of the more obvious techniques used when creating a virtual room, and is often heard as reverb or echo. Absorption is the method of blocking sound by large objects between the source of the sound and the position of the listener. An example of this could be a door, window or even large furniture. Sound travels around obstacles but results in muffling and volume alterations.

Sound diffraction is when a sound is heard that is not insight. An example of this could be a radio playing music in another room to the one the character is in. The sound is still heard even though you can not visually see the sound source. Sound refraction is the natural bending of the sound. Refraction can also add additional sound, which effectively amplifies the sound. An example of a natural amplifier is a large lake.

Limitations of game industry 

Game wants to run between 30 and 60 FPS 

Cannot “downgrade” the game for sound propagation 

Limited memory (2 to 50 MB for audio) 

Limited CPU (around 10% of the total CPU for audio) 

Up to 64 simultaneous sounds playing 

 At 60 FPS, that gives 250 ms per sound 

http://gdcvault.com/play/1015492/Real-time-Sound-Propagation-in

Due to the limitations of technology in the games industry not all game developers include a sophisticated sound propagation system. Here is an example of sound propagation being implemented in a game. The Dunia engine in Far Cry 2 enables sound propagation to be used to add extra depth to the games scenery. Interestingly the gamer is able to start a fire, which changes in sound depending on the position of the character and the addition of different landscape objects.

Another more obvious example of sound propagation is in the weather system for minecraft. The sound of rain changes when walking outside, as the gamer takes cover under trees or blocks, resulting in a much more realistic gaming experience.

Wave Types

Longitudinal Waves - Transverse Waves - Torional Waves

"To further increase immersive gameplay, several recent games (such as Valve's Half Life 2 and Crytek's Far Cry) have added an integrated physics and behavior engine to enhance that realism, as objects interact with one another in a more physically plausible way. In contrast, sound generation and propagation have not received as much attention due to the extremely high computational cost for simulating realistic sounds." - http://www.few.vu.nl/~A.Eliens/research/research/papers/@archive/science/p66-raghuvanshi.pdf

This clip shows how distance sound propagation can be perfectly emulated to enhance the gaming experience.

Below are some more examples and explanations of sound propagation in relation to digital rooms and games