HD-MAC

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HD-MAC was a proposed broadcast television systems standard by the European Commission in 1986 (MAC standard), a part of Eureka 95 project. It was an early attempt by the EEC to provide High-definition television (HDTV) in Europe. It was a complex mix of analogue signal (Multiplexed Analogue Components), multiplexed with digital sound. The video signal (1250 (1152 visible) lines/50 frames in 16:9 aspect ratio) was encoded with a modified D2-MAC encoder.

HD-MAC could be decoded by a standard D2-MAC receivers (SDTV), but in that mode only 625 (576) lines and certain artifacts were visible. To decode the signal in full resolution required a specific HD-MAC tuner.

PAL SDTV broadcasts use 6-, 7- (VHF), or 8 MHz (UHF). For HD-MAC, the transmission medium must guarantee a baseband bandwidth of at least 11.14 MHz.[1] This translates to a 12 MHz channel spacing in cable networks. For satellite broadcasting, due to FM modulation spectrum expansion, an entire satellite transponder would be used, resulting in 27 to 36 MHz of bandwidth.[2] Because UHF spare bandwidth was very scarce, HD-MAC was usable "de facto" only to cable and satellite providers, where their bandwidth was less constricted. However, the standard never became popular among broadcasters. For all this, analog HDTV could not replace conventional SDTV(terrestrial) PAL/SECAM, making HD-MAC sets unattractive to potential consumers.

It was required that all high-powered satellite broadcasters to use MAC from 1986. However, the launch of middle-powered satellites by SES and the use of PAL allowed broadcasters to bypass HD-MAC, reducing their transmission costs. HD-MAC (the high-definition variant of MAC) was left for transcontinental satellite links, however.

For the 1992 Winter Olympics and 1992 Summer Olympics, a public demonstration of HD-MAC broadcasting took place. 60 HD-MAC receivers for the Albertville games and 700 for the Barcelona games were set up in "Eurosites" to show the capabilities of the standard.[3] A CRT Video projector was used to create an image a few meters wide. There were some Thomson "Space system" 16/9 CRT TV sets as well. The project sometimes used Rear-projection televisions. In addition, some 80,000 viewers of D2-MAC receivers were also able to watch the channel (though not in HD). It is estimated that 350,000 people across Europe were able to see this demonstration of European HDTV. This project was financed by the EEC. The PAL-converted signal was used by mainstream broadcasters such as SWR, BR, and 3Sat.

The HD-MAC standard was abandoned in 1993, and since then all EU and EBU efforts have focused on the DVB system (Digital Video Broadcasting), which allows both SDTV and HDTV.

Technical details

The signal was captured with 50 full frames per second, each at a resolution of 2048×1152. This was only available behind the camera, though, as a source for the HD-MAC encoder, which could only transmit a reduced part of this video information. To increase horizontal resolution of the D2-MAC norm, only its bandwidth had to be increased. This was easily done as unlike PAL, the sound is not sent on a sub-carrier, but multiplexed with the picture. However, to increase vertical bandwidth was more complex, as the line frequency had to stay at 15,625 Hz to be compatible with D2-MAC. This offered three choices:

  • 50 frames per second with only 288 lines for fast moving scenes
  • 25 frames per second with 576 lines for normally moving scenes
  • 12.5 frames per second with all 1152 lines for slow motion

As none of the three modes would have been sufficient, the choice during encoding was not made for the whole picture, but for little blocks of 16×16 pixels. The signal then contained hints that controlled which de-interlacing method the decoder should use. To fully decode the picture, the signal had to be digitized and then read from the memory several times.

The bandwidth reduction process resulted in a final 1440×1152i/25 (50 Hz field rate, interlaced) reconstructed video signal at the receiver side.

See also

TV transmission systems

  • Analog high-definition television systems
  • PAL, what MAC technology tried to replace
  • SECAM, what MAC technology tried to replace
  • A-MAC
  • B-MAC
  • C-MAC
  • D-MAC
  • E-MAC
  • S-MAC
  • D2-MAC
  • HD-MAC, an early high-definition television standard allowing for 2048×1152 resolution.
  • DVB-S, MAC technology was replaced by this standard
  • DVB-T, MAC technology was replaced by this standard

Related standards:

References

  1. ↑ ETSI specification of the D2-HDMAC/Packet system (ETS 300 352), section 4.1
  2. ↑ ETSI specification of the D2-HDMAC/Packet system (ETS 300 352), section 10.3
  3. ↑ http://tech.ebu.ch/docs/techreview/trev_253-production.pdf, HDTV programme production, the development of 1250/50 HDTV, 3. The Olympic games

External links

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