Multiplexed Analogue Components
Encyclopedia
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
transmission standard, originally proposed for use on a Europe-wide terrestrial HDTV system, although it was never used terrestrially.
Technical overview
MAC transmits luminance and chrominanceChrominance
Chrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal . Chrominance is usually represented as two color-difference components: U = B' − Y' and V = R' − Y'...
data separately in time rather than separately in frequency (as other analog television
Analog television
Analog television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal...
formats do, such as composite video
Composite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...
).
Audio and Scrambling (selective access)
- Audio, in a format similar to NICAMNICAMNear Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
was transmitted digitally rather than as an FM sub-carrier. - The MAC standard included a standard scrambling system, EuroCryptEuroCryptEuroCrypt is a conditional access system for Multiplexed Analogue Components-encoded analogue satellite television. It had several versions . It supported receivers with card slots and those with embedded keys...
, a precursor to the standard DVB-CSA encryption system
History
MAC was originally developed by the Independent Broadcasting AuthorityIndependent Broadcasting Authority
The Independent Broadcasting Authority was the regulatory body in the United Kingdom for commercial television - and commercial/independent radio broadcasts...
(IBA) (dates unknown) in the UK for delivering high quality pictures via direct broadcast satellites that would be independent of European countries' choice of terrestrial colour coding standard.
Variants
A number of broadcasting variants of the MAC standard exist.- A-MACA-MACA-MAC carries the digital information: sound, data-teletext on an FM subcarrier at 7 MHz. Since the vision bandwidth of a standard MAC signal is 8.4 MHz, the horizontal resolution on A-MAC has to be reduced to make room for the 7 MHz carrier...
Designed as a test-bed for the MAC concept. A-MAC was never deployed by any broadcaster. S-MAC is design descendant A-MAC. - B-MACB-MACB-MAC is a form of analog video encoding, specifically a type of B-MAC is a form of analog video encoding, specifically a type of B-MAC is a form of analog video encoding, specifically a type of (Multiplexed Analogue Components (MAC) encoding. MAC encoding was designed in the mid 80s for use with...
used in South AfricaSouth AfricaThe Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
by MultichoiceMultiChoiceMultiChoice is a South African company which operates the DStv satellite television service, the main satellite TV service in Sub-Saharan Africa. It was formed out of the subscriber-management branch of the M-Net terrestrial pay TV company, and broadcasts the full range of M-Net channels on the...
, AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
by OptusOptusSingTel Optus Pty Limited is the second largest telecommunications company in Australia, and is a wholly owned subsidiary of Singapore Telecommunications...
and also used in parts of Asia until 2005 when digital compression finally replaced B-MAC. - C-MACC-MACC-MAC is the variant approved by the European Broadcasting Union for satellite transmissions. The digital information is modulated using 2-4PSK , a variation of quadrature PSK where only two of the phaser angles are used....
has a wide-screen backwardly compatible variant called E-MACE-MACE-MAC is 16:9 version of C-MAC. Originally E-MAC was designed for 15:9 pictures, it later adopted the 16:9 aspect ratio. The format is backwards compatible with C-MAC. It embeds additional information in field blanking and line blanking signals. E-MAC has a lower data capacity because of this...
. - D-MACD-MACAmong the family of MAC or Multiplexed Analog Components systems for television broadcasting, D-MAC is a reduced bandwidth variant designed for transmission down cable....
(used by British Satellite BroadcastingBritish Satellite BroadcastingBritish Satellite Broadcasting was a British television company which provided direct broadcast satellite television services to the United Kingdom...
) but not used on cable systems. This is a satellite only MAC format. Also used by NRK. This because D-MAC has 4 audio channels (D2-MAC just has 2 audio channels). Then it was possible to transmit 3 radio channels and 1 TV channel at one D-MAC channel. - D2-MAC used until July 2006 in Scandinavia and until the mid-1990s for German and French satellite television. Some cable systems may still be using D2-MAC in Europe and Asia.
- HD-MACHD-MACHD-MAC was a proposed broadcast television systems standard by the European Commission in 1986 . It was an early attempt by the EEC to provide High-definition television in Europe. It was a complex mix of analogue signal , multiplexed with digital sound...
, an early high-definition television standard allowing for 2048x1152 resolution.
Studio (non Broadcast) MAC variants
S-MAC (Studio MAC): Used mostly in North America.- Processing NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
component signals yields better results (a higher quality image) than manipulating NTSC directly – thus the need to create S-MAC. - It is not possible to mix standard MAC signals in the studio environment because the (R-Y) and (B-Y) components are carried on alternate lines.
- S-MAC's SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
like approach to bandwidth reduction is technical annoyance, but most studio users are not affected by it. - In S-MAC the luminance is compressed by 2:1 and the two chrominance signals by 4:1 so that all three may occupy the same line.
- S-MAC's vision bandwidth is 11 MHz, only ~2.8x that of NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
's vision bandwidth of 4.2 MHz. - S-MAC can be carried on a single circuit and converted losslessly to and from C-MAC at any stage.
- S-MAC is well suited for SNG applications (AKA: news gathering trucks).
MAC system innovations
Mathematical- A-MAC proved the mathematical principle that separating vision from colour for TV transmission was technologically viable.
Broadcast Engineering
- The MAC audio subsystem is very similar to NICAMNICAMNear Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
, so much so that identical chip-sets are used.
Broadcast engineering
- D-MAC satellite broadcasts provided the first broadcast sourced wide-screen television in Europe, and HD-MAC provided the first HDTV broadcasts, in 1992.
Technical challenges
Although the MAC technique is capable of superior video quality, (similar to the improvement of component video over composite in a DVD player), its major drawback was that this quality was only ever realized when the video signals being transmitted remained in component form from source to transmitter. If at any stage the video had to be handled in composite form, the necessary encoding/decoding processes would severely degrade the picture quality.- Terrestrial TV broadcasters were never able to take full advantage of MAC image quality due to multiple interactions between their composite and component signal paths.
- Direct to Home and TVRO broadcasters were able to take advantage of MAC's improved image quality because their studios and routing facilities were far less complex.
- The success of NICAMNICAMNear Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
audio for terrestrial television can be traced to the success of MAC technology. The MAC audio subsystem is nearly identical in design and function to NICAMNICAMNear Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
.
Technological obsolescence
Since the vast majority of TV stations and similar installations were only wired for composite videoComposite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...
, the fitting of a MAC transmitter at the end of the chain had the effect of degrading the transmitted image quality, rather than improving it.
For this and other technical reasons, MAC systems never really caught on with broadcasters. MAC transmission technology was made obsolete by the radically new digital systems (like DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
and ATSC) in the late 1990s.
Although MAC transmission systems are still used, the technology is obsolete. It is expected that MAC will cease to be used for TV transmission by 2012.
See also
TV transmission systems:- Analog high-definition television systems
- PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
, what MAC technology tried to replace - SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
, what MAC technology tried to replace - DVB-SDVB-SDVB-S is an abbreviation for Digital Video Broadcasting — Satellite; it is the original Digital Video Broadcasting forward error coding and demodulation standard for satellite television and dates from 1994, in its first release, while development lasted from 1993 to 1997...
, MAC technology was replaced by this standard - DVB-TDVB-TDVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
, MAC technology was replaced by this standard
External links
- Multiplexed Analogue Components in "Analog TV Broadcast Systems" by Paul Schlyter