DTV

(Digital TeleVision) Transmitting TV using digital signals. The major DTV standards are ATSC (North America), DVB (Europe) and ISDB (Japan). All three use MPEG-2 video compression and Dolby Digital audio compression. DVB and ISDB also include MPEG audio compression.

In the U.S., the FCC approved the ATSC standard in late 1996 (see ACATS). In 1998, DTV debuted in major U.S. cities, and the FCC mandated that broadcasters switch to digital by 2006 and turn off analog transmission. In 2005, the deadline was extended to February 17, 2009 (see digital TV transition). Other countries have adopted the ATSC format, including Canada, South Korea, Taiwan and Argentina.

A Digital TV or a Set-Top Box
To receive a DTV program requires a digital TV set or a digital set-top box for an analog TV. However, digital TV sets may continue to have analog inputs for many years, because people have huge collections of VHS movies and recordings.

Eighteen DTV Formats
DTV offers 18 digital formats starting with Standard Definition (SD), the digital counterpart of the NTSC analog standard, except without snow and ghosts. Enhanced Definition (ED) offers the most formats (see table below). High Definition (HD) provides 5.1 Dolby Digital Surround Sound and requires a wide screen TV set (16:9) in order to eliminate the letterbox effect. Increasingly, programs are being transmitted in HDTV.

As you can see from the table below, the numerous options provide the broadcaster with a tradeoff between how many channels can be sent versus channel quality. The more HD channels, the fewer ED and SD channels, and vice versa. See digital TV transition, HDTV, letterbox, NTSC, 8-VSB, interlace, digital cable and cliff effect.

        p = progressive scan (non-interlaced)
        i = interlaced

                            Frame
      Resolution    Aspect  Rate    Pixel
      Horiz x Vert  Ratio   (fps)   Shape

  HD - High Definition TV (HDTV)
   1. 1920 x 1080   16:9    24p     Square
   2. 1920 x 1080   16:9    30p     Square
   3. 1920 x 1080   16:9    30i**   Square

   4. 1280 x  720   16:9    24p     Square
   5. 1280 x  720   16:9    30p     Square
   6. 1280 x  720   16:9    60p**   Square

  ED - Enhanced Definition TV (EDTV) - 480p
   7. 704 x  480   16:9     24p     Rectangle
   8. 704 x  480   16:9     30p     Rectangle
   9. 704 x  480   16:9     60p**   Rectangle

  10. 704 x  480    4:3     24p     Rectangle
  11. 704 x  480    4:3     30p     Rectangle
  12. 704 x  480    4:3     60p**   Rectangle

  13. 640 x  480    4:3     24p     Square
  14. 640 x  480    4:3     30p     Square
  15. 640 x  480    4:3     60p     Square

  SD - Standard Definition TV (SDTV) - 480i
  16. 704 x  480   16:9     30i     Rectangle
  17. 704 x  480    4:3     30i**   Rectangle

  18. 640 x  480    4:3     30i     Square

 ** = most popular formats


  RELATED FORMATS:

  DVD - DV/MiniDV
      720 x 480 x 30 fps (NTSC)
      720 x 576 x 25 fps (PAL/SECAM)
       Only 704 of the 720
        horizontal pixels are visible.

  D1 Broadcast Format
      720 x 486 x 30 fps (NTSC)
      720 x 576 x 25 fps (PAL/SECAM)

SDTV Vs. HDTV

The 4:3 aspect ratio on standard TV and computer screens (left) is more square than the 16:9 ratio of wide screen sets (right). (Image courtesy of Intergraph Computer Systems.)