Digital eXtreme Definition.


DXD is s plain PCM with 24 bit / 352.8 kHz
As DSD (single bit) is not suit for editing, this format was developed for the Merging Pyramix workstation and introduced together with their Sphynx 2, AD/DA converter in 2004. This combination meant that it was possible to record and edit directly in DXD, and that the sample only converts to DSD once before publishing to SACD. 


Source: Wikipedia