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ciderdude
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A question about Hertz

Post by ciderdude »

Apologies if this is a dumb question.

When I bought a new Telly a couple of years back I noticed that, despite the TVs 100HZ capability, when viewing TV via my Toppy the TV only operates at 50HZ. It doesn't appear possible to up it to 100HZ. I quickly came to the conclusion that this is probably a limitation of the Toppy or SCART or perhaps the SCART port on the rear of the Telly. I am sure that there is someone out there that can enlighten me on the subject.

Anyway, I am in the process of looking for a new Telly for my parents and am reading various on-line reviews about the current crop of LCD TVs on the market. One of the key metrics that gets mentioned in almost every review is Hertz. Some do 50 others do 100 or 200, and some even claim 400. However, my parents source is an ancient and venerable SKY box. It isn't SKY+ or even SKY HD, just a plain old SKY box (thompson I think) that hooks up via a SCART or a good old COAX aerial cable, its so old its silver :shock:. There are currently no plans to upgrade to a more modern sky offering due to the perceived expense.

So, as with the Toppy, am I right in assuming that the best they will get from the old SKY box is 50HZ regardless of the capabilities of the TV?
alan_m
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Re: A question about Hertz

Post by alan_m »

ciderdude wrote:Apologies if this is a dumb question.

When I bought a new Telly a couple of years back I noticed that, despite the TVs 100HZ capability, when viewing TV via my Toppy the TV only operates at 50HZ. It doesn't appear possible to up it to 100HZ.
All UK broadcasts are only 50Hz. TVs that claim 100Hz functionality are creating an extra picture for between two broadcast pictures. In some cases it can appear to improve the viewing experience. In other cases the TV can get it so wrong that it degrades your viewing experience. On my TV I have this feature turned off.

Some TV claim 200 or 400Hz - this is mainly B*** S*** and there to simply fool the people who believe big numbers are better. It is doubtful that even the best LCD TV can panels can respond to so fast a change.
I quickly came to the conclusion that this is probably a limitation of the Toppy or SCART or perhaps the SCART port on the rear of the Telly. I am sure that there is someone out there that can enlighten me on the subject.
It's nothing to do with your Toppy although it could be a limitation on the TV AV input method. On my TV the 100Hz function works on the SCART inputs (RGB).
Ex Toppy 5800 user - now migrated to Xtrend ET10000 Enigma 2 box with 2 terrestrial and 2 satellite tuners. Second box Zgemma H9S (Enigma 2, satellite)
nvingo
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Post by nvingo »

Hi, someone with more knowledge than I may come along and fill in where I miss anything.

Basically before there was any storage in TVs, the screen had no option than to show the signal as it arrived.

In UK the standard definition signal is colour encoded to PAL standard with 25 frames per second interlaced to 50 fields (ie. fields 1,3,5.. start on even scan lines and 2,4,6.. start on odd scan lines).

With larger screens there is an effect where the human eye is more more sensitive to flicker caused by the persistence of the phosphor in a CRT television screen (each pixel is energised when the electron beam scans it, then decays for 1/25th second until it is refreshed during the next field scan). There is a similar effect with LCDs due the need to switch each pixel fast enough to eliminate the smearing traditionally visible on this type.

So a TV set can now store each 50Hz field and scan it onto the screen twice, ie. at 100Hz, or multiple times depending on the native speed of the display panel.

However, the TV may still tell you the rate of the incoming signal, ie. 50Hz PAL or 60Hz NTSC (USA standard).
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ciderdude
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Location: Milton Keynes

Post by ciderdude »

That makes sense. I suspect therefore that my TV is just telling me what the incoming signal is.

Thanks folks.
ROWANMOOR
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Post by ROWANMOOR »

Try looking at your TV (when you know it is in 100Hz mode) and a 50Hz CRT out of the corner of your eye. You should be able to see the difference - one will seem to flicker, the other won't. If you can then try it showing the Toppy picture and you should be able to tell.

Personally I can see the difference looking directly at the picture of just about any size screen now as I am so used to only seeing 100Hz or LCDs for many years. I find it quite uncomfortable to watch a 50Hz screen these days!
Cheers,
Rowan.


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