DTV is a set of digital television standards set forth by ATSC and bound to replace NTSC in the
DTV has certain advantages over NTSC. It uses less bandwidth per channel than NTSC requiring a narrower spectrum of radio frequencies. It allows for multichannel sound, electronic program guides, interactivity and other amenities.
In practical implementation DTV is compressed using lossy MPEG-2 codec sometimes resulting in picture artifacts.
HDTV is a subset of DTV standards. DTV is not necessarily in high definition but it defines a number of HD standards proposed for use in the