Albert's Attic Gallery

IBA Engineering Information Service:
'C-MAC, A Television System for Satellite Broadcasting', 1984

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A year after BBC Information Sheet 5001 appeared, the Independent Broadcasting Authority Engineering Information Service published 'C-MAC, A Television System for Satellite Broadcasting'.

Multiplexed Analogue Component, or MAC, was invented by the IBA's boffins. The IBA was justifiably proud of MAC, and the publication extols its virtues in no small way. MAC was a 625-line system, but it differed from PAL in two significant ways. Firstly the sound was carried as a digital signal within the line-blanking interval, so there was no separate sound carrier. Secondly, the colour and luminance signals contained in each scanning line were transmitted sequentially, rather than 'mixed up together' as with PAL. This gave RGB-type picture quality, since the PAL cross-colour shortcomings were eliminated. This very clever idea was a real leap forward. It was a brilliant achievement for the IBA's R & D people, and of course, it was British!

Why then, aren't we all watching MAC television as the 21st century gets under way? And why, if MAC sound was to be digital, was the picture to remain analogue? The two questions have the same answer. With hindsight, MAC was a halfway house between analogue and digital television. The MAC picture couldn't be digital because the technology (well, the processing power) wasn't ready. Digital picture transmission was 'not practicable.' As soon as it became practicable, well, that was the end of MAC. Another major blow was Sky's early decision to stick with PAL. In commercial terms Sky was absolutely right, of course. They needed a cheap no frills method of getting TV pictures to the viewer. They believed, correctly, that the vast majority of their potential audience didn't give a damn about the finer points of picture quality - couldn't even tell the difference, in fact. Sad but true, and of course in the end Sky won the day.

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