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DTV - technical definition

Referring to television in digital, rather than analog, form. As is the case with digital communications, in general, DTV offers the advantages of enhanced bandwidth efficiency through compression, improved signal quality due to reduced noise, and enhanced overall management and control. DTV does not suffer from the ghosting, snowy images, and generally poor audio quality associated with analog TV. Issues of signal quality in DTV transmission manifest in artifacts such as blocking, or tiling, and stuttering. Digital video content benefits from enhanced processing, storage, and manipulation. 1 2 3 A 4 5 6 B 7 8 9 C * 0 # D Hz 1209 1336 1477 1633 697 770 852 941 More specifically, digital content advantages include editing, alteration (e.g., morphing), reproduction, compression, and store-and-forward capability. DTV standards include high definition television (HDTV) and standard definition television (SDTV). The ATSC standards specify MPEG-2 compression, and the transport subsystem as ISO/IEC 13818. Packet transport involves a serial data stream of packets of 188 octets, one octet of which is a synchronization byte and 187 octets of which are payload. This packet approach is suitable for ATM switching, as each 188-octet MPEG-2 packet maps into the payload of four ATM cells, with only 4 octets of padding required. SDTV employs Reed-Solomon forward error correction (FEC) and 8-level vestigial sideband (8 VSB) RF modulation to support a bit rate of 19.28 Mbps over a 6 MHz terrestrial broadcast channel. Audio compression is based on the AC-3 specification from Dolby Digital and the ATSC. SDTV standards were developed by the Grand Alliance and reviewed, tested, and documented by the Advanced Television Systems Committee (ATSC) at the request of the United States Federal Communications Commission (FCC). See also 8-VSB, AC-3, analog, artifact, ATM, ATSC, bandwidth, broadcast, byte, channel, compression, digital, DTV, FCC, FEC, ghosting, Grand Alliance, HDTV, modulation, MPEG-2, NTSC, octet, packet, padding, PAL, payload, Reed-Solomon, RF, SDTV, SECAM, signal, store and forward, synchronize, TV, and video.

See DTV in Computer

(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, and then to June 12, 2009 at the last minute (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, TV converter box, 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.)

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