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GETTING STARTED 1 – 50/100 Hz DISPLAYS

 

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It's all down to an effect known as 'Large Area Flicker'. The picture on small to medium size TVs, up to screen sizes of 28-inches, say, look fine, but on larger screens and especially widescreen displays – and that's where most of us are heading nowadays -- a lot of people begin to notice that TV pictures flicker, especially in bright areas and the corners of the image. That's because a normal TV picture is made up of a sequence of static images or 'fields', shown 50 times second, (hence they are known as '50Hz' sets). Our eyes, courtesy of an effect called persistence of vision, blends the rapid succession of still images into fluid movement, but only just, and as the picture gets larger flickering becomes more apparent and for some people it can be really annoying.

 

The solution is to increase the number of fields shown every second using a technique known as 100Hz. The normal 50Hz picture is digitally reprocessed so that 50 picture fields are shown twice every second. This very neat electronic conjuring trick cures large area flicker but it creates a whole new set of problems. Early 100Hz TVs were not very good at rendering fast movement – the small differences in successive fields was exaggerated by showing them twice -- resulting in a jerky or blurred picture. Some systems also have trouble dealing with the huge amount of information in a 'busy' picture, which led to 'blocky' images or processing 'artefacts'. In the past few years 100Hz display systems have improved enormously, but inevitably some are better than others. If you are in the market for a 100Hz TV – and you should make it a priority on large screen sets -- try to see a few models in action, preferably showing a lot of movement, like a football match or motor race.  

 

 

GETTNG STARTED 2 – AV LINK

 

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A lot of TVs and video recorders these days can 'talk' to each other through the SCART cable connection that carries picture and sound signals, but what makes it interesting is that it works on products from competing manufacturers. The system, originally called Project 50 was based on an earlier system called D2B or the Domestic Digital Bus, which was meant to unify the control systems of a whole range of household domestic appliances – from fridges and washing machines to central heating systems -- by allowing them communicate with one another. The present system, now generically known as AV Link, has been greatly simplified and is specific to just TVs and video recorders.

 

It comes in various branded forms, including NexTViewLink (Ferguson, Toshiba, Sharp, Thomson, Panasonic), Q-Link (Panasonic again), MegaLogic (Grundig), EasyLink (Philips) and SmartLink (Sony). To make things even more confusing there are several different implementations or levels of sophistication, though the basic system has six core functions (but not all products support them…).

 

Nevertheless, most AV Link compatible TVs and VCRs usually have One Touch Record, where pressing one button on the VCR remote records whatever channel is being shown on the TV at the time, and Tuner Download, which speeds up VCR installation by copying the contents of the TVs tuner to the video recorder. One Touch Play is also quite common; this switches on the TV when you load a tape into the VCR and press the Play button and a lot of products also have auto power off, whereby the TV will switch off automatically after the VCR has finished playing a tape. Other less frequently seen functions, which tend to rely on the TV and VCR coming from the same manufacturer, include One Touch Video Plus+ (simpler timer programming) and One Touch Menu, where the TV and VCR share a common on-screen display system.

 

 

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Σ R. Maybury 2001, 0904

 

 

 

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