Open Al

OpenAL supports rendering audio in '3D' similar to how OpenGl allows rendering video in 3D. It allows one to identify audio 'sources', as well as the listener, as moving about in 3D space. It processes the sources for attenuation, doppler shift, etc.

But it's still incomplete, as it doesn't handle reflection (echo), or muffling of a sound that goes through a door.

OpenAL is available under LGPL.