Multiplexed Analogue Components
Multiplexed Analogue Components (MAC) was an analog television standard where luminance and chrominance components were transmitted separately. This was an evolution from older color TV systems (such as PAL or SECAM) where there was interference between chrominance and luminance.
Originally proposed in the 1980s for use on a Europe-wide terrestrial HDTV system, although it was never used terrestrially. However, tests have been done in France with terrestrial transmission but no commercial exploitation.

Various systems were developed, collectively know as the "MAC/packet" family. In 1985 these were recommended for satellite and cable broadcasts by the EBU. C-MAC/packet was intended for Direct Broadcast Satellite (DBS), D-MAC/packet was intended for wide-band cable, and D2-MAC/packet was intended both for DBS and narrow-band cable.

History 
MAC was originally developed by the Independent Broadcasting Authority (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.

In 1982 it was adopted as the transmission format for the UK's forthcoming direct broadcast satellite (DBS) television services (eventually provided by British Satellite Broadcasting). The following year MAC was adopted by the European Broadcasting Union (EBU) as the standard for all DBS.

By 1986, despite there being two standards, D-MAC and D2-MAC, favoured by different countries in Europe, an EU Directive imposed MAC on the national DBS broadcasters, to provide a stepping stone from analogue PAL and Secam formats to the eventual high definition and digital television of the future, with European TV manufacturers in a privileged position to provide the equipment required.

However, the Astra satellite system was also starting up at this time (the first satellite, Astra 1A was launched in 1989) and that operated outside of the EU's MAC requirements, due to being a non-DBS satellite. Despite further pressure from the EU (including a further Directive originally intended to make MAC provision compulsory in TV sets, and a subsidy to broadcasters to use the MAC format), most broadcasters outside Scandinavia preferred the lower cost of PAL transmission and receiving equipment.

In the 2000s, the use of D-MAC and D2-MAC ceased when satellite broadcasts changed to DVB-S format.

Variants 
A number of broadcasting variants exist, according to the way the digital signals are multiplexed with the MAC vision signal.
 A-MAC 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-MAC used in South Africa by Multichoice, Australia by Optus. Used in the US by Primestar and American Forces Radio and Television Service. Used in parts of Asia until 2005 when it was replaced by digital compression. 
 C-MAC required a bandwidth of about 22MHz, making it problematic for broadcasting. It could carry eight high quality (15 kHz bandwidth) sound channels. It has a wide-screen backwardly compatible variant called E-MAC.
 D-MAC was a UK standard (used by British Satellite Broadcasting) for satellite broadcasts, needing a bandwidth of approximately 10.5 MHz. It could carry eight high quality (15 kHz bandwidth) sound channels Used in Norway by NRK, transmitting 3 radio channels and 1 TV channel at one D-MAC channel.
 D2-MAC further reduces the bandwidth to 7.8 MHz allowing usage on cable and satellite broadcast. It could carry four high quality (15 kHz bandwidth) sound channels or eight lower quality audio channels. Adopted by Germany and France, it was used on satellite broadcasts (TV-Sat 2, TDF 1 and TDF 2). The system was used  until July 2006 in Scandinavia and until the mid-1990s for German and French sound channels. Some cable systems may still be using D2-MAC in Europe and Asia.
 HD-MAC, 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 NTSC 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 SECAM 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 NTSC'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).

Technical overview 
MAC transmits luminance and chrominance data separately in time rather than separately in frequency (as other analog television formats do, such as composite video). This allows for full separation of the components.
The signals are also time-compressed (with ratios of 3:2 for luminance and 3:1 for chrominance) and the two color difference signals are transmitted on alternate lines, further increasing compression. The color space was YPbPr, with a luminance component and red blue color difference chrominance components.

Audio and scrambling (selective access) 
 Audio, in a format similar to NICAM was transmitted digitally rather than as an FM sub-carrier.
 The MAC standard included a standard scrambling system, EuroCrypt, a precursor to the standard DVB-CSA encryption system

Technical details 
In MAC color is encoded using the YPbPr color space. Luma () is derived from red, green, and blue () after gamma-correction (formula similar to PAL):
 

Color information is computed based on B-Y and R-Y differences, generating two compressed and weighted color-difference signals know in older MAC references as E'Um and E'Vm or CB and CR. To avoid any confusion, and since the signals are analogue and bi-polar, these terms were replaced by PB and PR.
 
 and  are used to transmit chrominance.  On C-MAC, D-MAC and D2-MAC the following formulas apply: 

 

Luminance signal range is -0.5 to 0.5 volts; color difference signals vary between -0.65 to 0.65 volts.

The following table lists the main technical parameters of the various MAC variants:

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 NICAM, 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 NICAM 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 NICAM.

Countries and territories that used MAC
This is a list of nations that used the MAC standard for television broadcasting:

Technological obsolescence 
Since the vast majority of TV stations and similar installations were only wired for composite video, 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 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
 PAL, what MAC technology tried to replace
 SECAM, what MAC technology tried to replace
 DVB-S, MAC technology was replaced by this standard
 DVB-T, MAC technology was replaced by this standard

References

External links 
 Multiplexed Analogue Components in "Analog TV Broadcast Systems" by Paul Schlyter
 IBA Engineering Announcement broadcast 3 February 1987 with more information on MAC

High-definition television
Satellite television
Television transmission standards
Television technology