Quick reply - ATSC is the digital broadcast standard that includes HDTV - NTSC is generally speaking the existing broadcast standard - The 622 can receive ATSC standards off the air but can't receive the NTSC signals - most of the non-hd boxes can receive local broadcast NTSC signals. The early HD boxes including the old DISH 6000 could receive both NTSC and ATSC signals but had other limitations (notably no compatibility with MPEG4). Hope this helps...