Sound Propagation and Acoustics in Video Games.

There are several factors that must be considered when designing a realistic acoustic space. Complex large spaces not only require size and material to be taken into account, but also the complex effects on sound that walls, doorways and certain materials create. Phenomena such as Reflection, Refraction, Occlusion and Diffraction create unique properties for travelling sounds that are difficult to re-create in a virtual setting. An example could be a player standing just to the side of a doorway of a room containing a sound source.

Using just stereo audio, this may appear as if the sound is faintly travelling to the player through the wall of the room they are standing beside. While this does give some indication of where the sound is emanating from, using effective sound propagation we could use occlusion to aid the player in in locating the sound, as they could more accurately identify the origin of the sound, giving the player more accurate direction when playing the game (as can be seen in Figure 1).

Available since 2013, TrueAudio is AMD’s digital signal processing chip that offloads audio processing to a dedicated processor on AMD GPUs, which means that in addition to real-time 3D sound processing being improved, the computational load that audio would place on a system is significantly reduced. The processor was intended to be an early easy-to-use implementation of 3D audio for developers but has found little use, as since its release it has only been used in four released games, one of these being Eidos’ Thief (2014). The Thief series has always had an emphasis on audio complementing its gameplay, the original Thief released in 1998 was possibly the first game released that attempted to use propagated sound as a core game mechanic. The developers mapped out an audio layer over the physical layer of the level in order to map the propagation of sound through the environment in an attempt to make the sneaking experience more immersive through audio.

The developers of Thief (Eidos, 2014) wanted to follow up on this and decided to use the AMD TrueAudio system to do so, allowing the developers to create immersive 3D reverberant spaces to the game without the need for a bespoke 3D audio system(see example below).

In a paper conducted by researchers at the University of North Carolina at Chapel Hill, researchers used their already well understood light raytracing algorithms to create a system of propagating sound that replicates light path tracing. This works by building paths from a camera that bounce around a scene before hitting a sound source, calculating the various properties of sound in real-time. This is a very effective way of producing both light rays and sound propagation at the same time. However, a large number of rays must be simulated to obtain a satisfactory result. Many of these rays are not used in calculating the final result making them a waste of processing power. While this method may prove too intensive for a lower end consumer PC, this research helps further advance the possibilities in advanced sound modelling in the future.

In conclusion

Sound Propagation in games is advancing slowly, but new advancements from companies such as AMD and Microsoft are making it potentially possible to accomplish the integration of more advanced Propagation systems to game engines very soon. This should make sound in games more immersive, in terms of ambience and player direction.

References:

Project Acoustics, Game Developers Conference 2019 – Hakon Strande & Noel Cross. Available at: https://www.youtube.com/watch?v=uY4G-GUAQIE&t=565s&ab_channel=MicrosoftGameStack

Wikipedia: AMD TrueAudio: https://en.wikipedia.org/wiki/AMD_TrueAudio#:~:text=True%20Audio%20Next,-A%20new%20version&text=The%20TrueAudio%20Next%20SDK%20was,GPUOpen%20suite%20in%20August%202016.

Interactive Sound Propagation with Bidirectional Path Tracing. Chunxiao Cao, Zhong Ren, Carl Schissler, Dinesh Manocha, Kun Zhou. State Key Lab of CAD&CG, Zhejiang University, University of North Carolina at Chapel Hill. Available link below:

http://kunzhou.net/zjugaps/bst/bst.pdf

How Thief’s Stealth System Almost Didn’t Work | War Stories | Ars Technica. Avaliable here: https://youtu.be/qzD9ldLoc3c?t=259