Audio is always an important part of a game, even more so in training simulations. Generally audio is done binaural, panning between the left and right ears to give a sense of hearing the direction of which the sound is emmitting. The last Virtual Technology class' subject was about spatial audio in Virtual Reality. With Virtual Reality it becomes that much more important to have a proper audio system to immerse the user into the world. There is a lot to learn when looking at how sounds and the human ears work in real life. One of the biggest aspects is how sounds are perceived differently depending on the direction it comes from. So called HRTFs (Head-Related Transfer Functions) are a sort of filter that changes the way the sound is perceived (YouTube video showcasing the difference between audio with and without HRTF in Counterstrike: Global Offensive can be found here). Another thing to take into account is how sound travels through space. Air itself already has effect on soundwaves, but so does every other material. Concrete absorbs and transfers sound differently that a piece of cloth does. There's even a difference in concrete that's connected to the world or disconnected. The students were tasked with finding a way to replicate some of these features in Unity and see how Unity handles audio. From itself Unity has a rather lacking audio feature. There's an option to enable 3D sound which opens up the option to use spatial audio, panning, rolloff, doppler effect and some other settings. Above all of this, hidden in the project settings, the audio source can be set to make use of HRTF filters, provided by Microsoft. Unity audio is relatively wholesome for simple average projects but lacks in features like reverbing sound from surfaces and materials. For our project we wanted to delve deeper into audio and Virtual Reality.
To demonstrate the differences and pros and cons between Steam Audio and Unity audio I created a scene with a concrete room and a few walls. Within this room there are two spheres that can be turned on and off. One uses Steam Audio and the other uses Unity audio. The spheres circle around the player, passing behind the concrete walls in its path. In case of the Unity audio sphere no difference can be heard when the sphere dissapears behind the concrete walls in the middle. The only noticible feature is the HRTF filters and the direction the audio comes from. The Steam Audio sphere on the other hand loses a lot of it's volume and higher pitches once it travels behind the walls. Sound becomes more clear once the sphere reaches the corners of the walls before being visible again. During the next Virtual Technology I let the teacher and some other students try the application and listen to the differences. With both spheres everybody was able to tell where the audio was coming from. Wether it was above or below them. The added value of Steam Audio however is the fact that the perceived sound changes based on the position of the source and the objects between the source and the player. Steam Audio offers more features like placing sound probes in the rooms where sound can in fact travel to better replicate the HRTF filters. For the KLM training simulation we decided to continue using Steam Audio. An airplane muffles sound in an interesting manner due to use of materials and shapes and Steam Audio has the power to simulate these filters.
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