WE HAVE WALLS!
Insulation, Resilient Channels, Drywall, Sound Insulating Glue, Drywall. That pretty much sums up everything in this entry...
Notice the big stack of drywall in the background of the first picture. Also, the cables pre-wired at the bottom left corner.
resilient channels installed over the insulation directly on the framing
drywall mounted on top of the resilient channels which decouples the walls from the frame which (in theory) should cut down on the transmission of low frequencies.