"March 2016 NVIDIA Voxel Ambient Occlusion (VXAO) Update: Derived from our Voxel Global Illumination technology, VXAO is a new cutting-edge Ambient Occlusion technique that improves upon HBAO+ to deliver the most realistic Ambient Occlusion shadowing seen to date in games.
With VXAO,
occlusion and lighting information is gathered from a ‘world space’ voxel representation of the scene, which takes into account a large area around the viewer. Included in this voxelization are objects and details currently invisible to the viewer, and those behind the viewer, too. The result is scene-wide Ambient Occlusion shadowing, instead of ‘screen space’ shadowing based on what you can currently see. This allows AO shadows to be cast into a scene from objects near to the player but just outside of their view, and from occluded objects in the distance large enough to affect the appearance of the scene.
In addition, VXAO’s precision and accuracy enables significantly improved Ambient Occlusion shadowing in detailed in-game environments. This is particularly evident in Crystal Dynamics’ Rise of the Tomb Raider, the first game to feature VXAO. As demonstrated below in our interactive comparisons, VXAO dramatically improves the quality of Ambient Occlusion shadowing in the game’s object and geometry-filled locations.
In this first set of comparisons, VXAO's precision is exemplified. Detailed objects spread across several layers are accurately and richly shadowed, light being cast and reflected in the room is accurately accounted for, and new AO shadows rendered."
http://www.geforce.com/whats-new/gu...b-raider-ambient-occlusion-nvidia-vxao-update
It seems like VXAO isn't applied in screen space, could easily explain the performance impact. It definitely is more accurate than typical SSAO and HBAO+ though, wondering how it compares against Epics own DFAO