Thanks: Develop Conference | John Broomhall | Tandem Events | Hugh Edwards

Rollercoasters in Planet Coaster are created by users. There cannot be much prediction in how their creations behave or unfold so the implementation of audio measures real-time data and uses speed, acceleration, vertical and lateral g-force and look angles to manipulate up to 15 layers of coaster audio simultaneously (describing wind, train and tracks).
Additionally, a threshold system generates one-shots (an additional 60 one-shot sounds) to simulate the clangs and bangs of mechanical couplings and car interactions with the track turning, rolling or banking. These are fired off when crossing pre-set angle-steps for pitch, roll and yaw.
To score a wide range of coaster creations, from very mild to insanely exciting creations, coder Ian Hawkins implemented a real time parameter compressor/limiter that uses threshold settings based on current highest speed reached on the current ride. Any value below that threshold but above 25 meters per second is dynamically compressed or expanded so that all coaster creations sound exciting even if a track is build to go really fast all the time. This fixed the problem of building our systems for the fastest tracks (best "dynamic range") but not leaving enough variation for slower coasters. Choosing to treat the lower speeds more dynamically, and compressing higher speeds (when many sounds provide variation)

The swooshes and reflection system, created with coder Jon Ashby, is derived from a sphere test on each side of the coaster. The spheres test for collision with simplified world geometry (physics world). Based on distance of intersection, RTPC's (real time parameter controls == data send from the game we can use to manipulate sounds) are used to send part of the coaster audio to specially prepared buses while dampening the direct (dry) signal to simulate reflections. The buses are then hard panned to the correct side. This system is super fast and is a good impressionistic compromise between ray-casting ( a more technically correct reflection system) and not acknowledging the environment at all.

Additionally, a pooled emitter system also creates fixed place sound emitters on intersection with the sphere which play swoosh loops. A progress RTPC controls Doppler and correctly fades the swooshes. We attach these to scenery and intersection track-pieces.
Larger objects, such as buildings and caves, contribute to the "reflection" system, while smaller object (such as scenery or struts) create swooshes audio. This relatively "simple" system of reflections and swooshes helps grounds coasters in their environment better and is cheap so we can run it in real time.