VALVE MAKES ALL STEAM AUDIO SDK SOURCE CODE AVAILABLE UNDER APACHE 2.0 LICENSE

Summary from the TLDR Web Dev newsletter

Valve has made the Steam Audio SDK fully open-source, with plug-ins included. Steam Audio is an immersive audio solution for games and VR. It has real-time sound propagation, VR integration, and 3D audio capabilities. There are plug-ins to make it compatible with Unity, Unreal Engine, and other game engines.