A term bearing little or no implications for transmission and display systems. The SMPTE and the ATSC have approved one standard for HDEP, sometimes referred to as SMPTE 240M. This standard has 1125 scanning lines per frame, 60 field per second, 2:1 interlace, an aspect ratio of 16:9, extended colorimetry, and a 30 MHz base bandwidth for each of its three color components. It is based on work at NHK, but includes considerable American modifications.

Clearly, the combined 90 MHz base bandwidth of this DHEP standard cannot be practically broadcast (not counting sound or modulation characteristics, it takes up as much bandwidth as 15 current broadcast channels).

That is why there are so many ATV transmission schemes.