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Problems today with muxes 7 and 8



 
 
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  #21  
Old January 26th 18, 08:13 AM posted to uk.tech.digital-tv
Woody[_5_]
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Default Problems today with muxes 7 and 8


"Mark Carver" wrote in message
...
On 26/01/2018 08:38, Woody wrote:

There was that and the NIT, but having slept on it ISTR it was
something to do with Ch4 analogue with Sony TVs maybe 10 years ago?


Yes, but 20 years ago ! When C4 adopted PAL+ in 1994, part of that
was the requirement to have widescreen signalling on VBI line 23.

On widescreen sets, this was to enable 'zoom' mode to fill the
screen
on 16:9 letterbox material. That was fine, however for 4:3
transmissions Sonys decoded the 4:3 WSS ident as a command to go
into
that horrible non linear 'Smart Zoom' mode.
There was nothing much that could be done, as it was
more or less hard coded into the electronics, the only cure was for
C4 not to carry any WSS ident during 4:3 programming, and the
affected Sonys would then just sit in 4:3 mode. (C4 didn't do that,
arguing
quite rightly it was Sony's problem, not theirs)

It also caused the same problem once DTT/D-Sat started, and some
boxes
would use the L23 WSS commands.



No, it wasn't that. It was since I was in NTL and that didn't occur
until 1999. May even have been since I was based at Emley and that was
2004.


--
Woody

harrogate3 at ntlworld dot com


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  #22  
Old January 26th 18, 09:57 AM posted to uk.tech.digital-tv
NY
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Posts: 1,329
Default Problems today with muxes 7 and 8

"Mark Carver" wrote in message
...
On 26/01/2018 08:38, Woody wrote:

There was that and the NIT, but having slept on it ISTR it was
something to do with Ch4 analogue with Sony TVs maybe 10 years ago?


Yes, but 20 years ago ! When C4 adopted PAL+ in 1994, part of that was the
requirement to have widescreen signalling on VBI line 23.

On widescreen sets, this was to enable 'zoom' mode to fill the screen
on 16:9 letterbox material. That was fine, however for 4:3 transmissions
Sonys decoded the 4:3 WSS ident as a command to go into
that horrible non linear 'Smart Zoom' mode.
There was nothing much that could be done, as it was
more or less hard coded into the electronics, the only cure was for
C4 not to carry any WSS ident during 4:3 programming, and the affected
Sonys would then just sit in 4:3 mode. (C4 didn't do that, arguing
quite rightly it was Sony's problem, not theirs)

It also caused the same problem once DTT/D-Sat started, and some boxes
would use the L23 WSS commands.


And you've got the extra problem that some broadcasters, such as the various
BBC channels, transmit permanently in widescreen, whereas others, especially
the low-budget repeats channels such as ITV3, Drama, Yesterday toggle the
WSS flag between 4:3 programme and 16:9 adverts/trailers.

BBC's approach means that 4:3 archive programmes are transmitted in a 16:9
frame, so the centre portion of the 720 pixel frame width contains picture
info and a lot of horizontal resolution is being wasted in the black bars on
either side. I think it means that 4:3 programmes have a picture resolution
of 544x576 - the same as ITV3, Drama, Yesterday - instead of devoting the
full 720 pixels to programme. (OK, I know that BBC use 704 rather than 720
pixels, as can be seen by analysing off-air MPG recordings of BBC versus
ITV/CH4.

  #23  
Old January 26th 18, 10:00 AM posted to uk.tech.digital-tv
NY
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Posts: 1,329
Default Problems today with muxes 7 and 8

"Mark Carver" wrote in message
...
On 26/01/2018 08:53, NY wrote:
"Mark Carver" wrote in message



I wonder whether the SFN will lead to null areas of the country where two
(or more) transmitters happen to combine destructively so as to produce a
minimum signal level. Bad luck for anyone who lives in one of those
areas. :-(


Well indeed. The change of GI yesterday, is to reduce the occurrence of
those areas, but it will be interesting to see what happens as more
and more transmitters move to 55/56. We won't know for a while yet, Mendip
and Waltham are well separated !


I'm intrigued how a change in the coding of data within the UHF channel can
reduce the size of the null areas. Or does it lower the threshold signal
level where the digital cliff occurs, and make the receiver more tolerant of
weak signal?

  #24  
Old January 26th 18, 10:12 AM posted to uk.tech.digital-tv
Mark Carver[_2_]
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Posts: 439
Default Problems today with muxes 7 and 8

On 26/01/2018 11:00, NY wrote:

I'm intrigued how a change in the coding of data within the UHF channel
can reduce the size of the null areas. Or does it lower the threshold
signal level where the digital cliff occurs, and make the receiver more
tolerant of weak signal?


Read on, and Section 2.2 is particularly relevant

https://www.radioeng.cz/fulltexts/20...04_002_006.pdf


--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #25  
Old January 26th 18, 01:21 PM posted to uk.tech.digital-tv
Richard Tobin
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Posts: 1,383
Default Problems today with muxes 7 and 8

In article ,
NY wrote:

BBC's approach means that 4:3 archive programmes are transmitted in a 16:9
frame, so the centre portion of the 720 pixel frame width contains picture
info and a lot of horizontal resolution is being wasted in the black bars on
either side. I think it means that 4:3 programmes have a picture resolution
of 544x576 - the same as ITV3, Drama, Yesterday - instead of devoting the
full 720 pixels to programme.


But if they use the same bandwidth, those 544 pixels will be higher quality.

-- Richard
  #26  
Old January 26th 18, 02:00 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,329
Default Problems today with muxes 7 and 8

"Richard Tobin" wrote in message
news
In article ,
NY wrote:

BBC's approach means that 4:3 archive programmes are transmitted in a 16:9
frame, so the centre portion of the 720 pixel frame width contains picture
info and a lot of horizontal resolution is being wasted in the black bars
on
either side. I think it means that 4:3 programmes have a picture
resolution
of 544x576 - the same as ITV3, Drama, Yesterday - instead of devoting the
full 720 pixels to programme.


But if they use the same bandwidth, those 544 pixels will be higher
quality.


Sometimes pixel resolution means more than degree of JPEG compression.

  #27  
Old January 26th 18, 04:00 PM posted to uk.tech.digital-tv
Scott[_2_]
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Posts: 1,344
Default Problems today with muxes 7 and 8

On Thu, 25 Jan 2018 20:10:34 +0000, Mark Carver
wrote:

On 25/01/2018 19:58, Woody wrote:


Don't I remember something about Sony's having problems when another
component of DTTV changed some years ago? Can't for the life of me
remember what parameter it was but ISTR there was talk of a software
update to cure it.


Audio glitches whenever the HD transmission dynamically changed from
1080-50i to 1080-25p (or back). To be fair a number of manufacturers
had similar problems with that switching.


I seem to recall there was also a problem with the aspect ratio, which
you (Mark) resolved for me on this forum.
  #28  
Old January 26th 18, 04:43 PM posted to uk.tech.digital-tv
Paul Ratcliffe
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Posts: 2,486
Default Problems today with muxes 7 and 8

On Fri, 26 Jan 2018 10:57:50 -0000, NY wrote:

BBC's approach means that 4:3 archive programmes are transmitted in a 16:9
frame, so the centre portion of the 720 pixel frame width contains picture
info and a lot of horizontal resolution is being wasted in the black bars on
either side.


We're currently digitising our Beta SP tape archive using that principle.
And we won't mention the U-matic saga...
  #29  
Old January 26th 18, 05:48 PM posted to uk.tech.digital-tv
Mark Carver
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Posts: 7,633
Default Problems today with muxes 7 and 8

On 26/01/2018 17:00, Scott wrote:
On Thu, 25 Jan 2018 20:10:34 +0000, Mark Carver
wrote:

On 25/01/2018 19:58, Woody wrote:


Don't I remember something about Sony's having problems when another
component of DTTV changed some years ago? Can't for the life of me
remember what parameter it was but ISTR there was talk of a software
update to cure it.


Audio glitches whenever the HD transmission dynamically changed from
1080-50i to 1080-25p (or back). To be fair a number of manufacturers
had similar problems with that switching.


I seem to recall there was also a problem with the aspect ratio, which
you (Mark) resolved for me on this forum.


Ah, was that to do with having to set the underscan (Full Pixel) mode in
both i and p modes ?


--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #30  
Old January 26th 18, 06:07 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 2,448
Default Problems today with muxes 7 and 8

On 26/01/2018 08:56, Mark Carver wrote:
On 26/01/2018 08:53, NY wrote:
"Mark Carver" wrote in message



I wonder whether the SFN will lead to null areas of the country where
two (or more) transmitters happen to combine destructively so as to
produce a minimum signal level. Bad luck for anyone who lives in one
of those areas. :-(


Well indeed. The change of GI yesterday, is to reduce the occurrence of
those areas, but it will be interesting to see what happens as more
and more transmitters move to 55/56. We won't know for a while yet,
Mendip and Waltham are well separated !


We had some experience of these problems, albeit in the analogue days.
Certainly coverage was 'interference limited' rather than 'field
strength limited' in many areas. However it will be easier with digital
because the directional characteristics of a good aerial will go a long
way towards obtaining a signal/noise ratio adequate for decoding.
Remember that we will be able to choose the stronger of the two signals
and align the aerial in that direction.

Bill
 




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