BBC HD1

The geometry on a CRT is affected by the tube's angle to the Earth's magnetic field (and any local sources). When I moved house my picture got a droop to the right that I haven't been able to correct with the controls available in the service menu, so perhaps I should avoid this one.



Why isn't it feasible? Isn't it easier to leave the SD alone than convert it up to 100Hz (making it progressive in the process, as I understood it)?

David

Is that why BBC HD dosen't work in a Humax HDCI-2000 box then?

Domestic TVs can only work efficiently at a small range of line-scan rates - due to the requirement to optimise the line-scan transformer frequency response etc. Multi-sync technologies aren't really suitable for large, bright screens, they are usually both dimmer and more expensive.

The line-scan rates for 576/100i, 576/50p, 1080/60i, 480/120i (not used), 480/60p and 1080/60i are all very similar (around 32-33kHz)

The line-scan rates for 480/60i and 576/50i are much lower (around 15.625-15.75kHz) Similarly the line-scan rates for 720/60p and 720/50p are significanlty higher than those above - so usually CRT displays have to convert 720/60p and 480/60i - 576/50i to another format that has a more similar line-scan rate. (That is what happens on CRT HD displays in the US)

In the US they convert 480/60i to 480/60p for display - as they don't have a 50Hz flicker issue. In the UK they've chosen to convert 576/50i to 576/100i - the same line rate change, but a doubling of vertical refresh rate.

No - all DVB-S2 receivers are backwards compatible with DVB-S - the Humax issue isn't an S vs S2 issue - it is a difference to the way H264 video streams are flagged.

There are two ways that you can indicate that a stream is H264 - Sky and the BBC are using one, other European broadcasters are using another. The Humax receiver, until it gets an over the air upgrade which is expected very soon, only recognises one of the two indicators - so ignores the Sky and BBC H264 streams. (Last I heard Discovery HD was FTA H264 DVB-S2 and BBC HD1 was FTA H264 DVB-S, and the Humax ignores them both. The Sky HD channels - Discovery is not a Sky channel - are all encrypted now . Discovery will, I'm sure, encrypt soon if it hasn't already)

Thanks for the comprehensive explanation!



50i to 100i... do you know how they do that? Do they have to go via 50p anyway before to interpolate the extra fields? Do you know if it looks any "smoother" than 50p?

I took a look at a 100Hz TV last time I needed a new set. 2001 looked fantastic on it, but when I tried some 50i with horizontalling scrolling credits it didn't know what to do with itself and made them unreadable.

David

Different 100Hz systems use different algorithms - some preserve original fields and interpolate missing fields, others interpolate everything.

Some systems also add "Natural Motion" which can interpolate 25Hz motion (i.e. film and 25p video) to 50Hz motion - though I don't think any currently interpolate 50Hz or 25Hz to full 100Hz motion, I don't think any try to add anything above 50Hz.

Crawling and rolling credits often run quite quickly, which make them demanding to upconvert - as do semi-transparent moving objects (as you end up with motion in multiple directions for the same pixel..)

HDTV pixels aren't square, they're 16:9ish shape, so the image appears correctly on an HDTV screen, but not a PC monitor.

They can be square, but in this case they aren't, and nor are they 16:9. 1440x1080 (a ratio of 4:3) pixels are being broadcast for a 16:9 frame, making each pixel 4:3 (4:3²=16:9).

David

Thanks.

I did get it the first two times though

Only for that dimension, but 1280 x 720 and 1920 x 1080 are square pixels, which can be seen correctly on a PC.

That's for the detailed technical answer, very much appreciated noggin