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Predicting com7/8 SFN reception deterioration due to CCI



 
 
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  #101  
Old Yesterday, 11:46 AM posted to uk.tech.digital-tv
Alex[_6_]
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Default Predicting com7/8 SFN reception deterioration due to CCI


"Indy Jess John" wrote in message ...

I also dislike the idea of throwing away perfectly serviceable equipment
just so that somebody can have the screen resolution to count the number
of twigs on a tree in winter.


Ordinarily I'd agree, but DVB-T was so bad, it was basically unfit for purpose. When its original incarnation, in the form of OnDigital (later ITV Digital) failed, many consumers cited poor picture quality as their reason for rejecting it. The collapse of these services should have been taken as an opportunity to upgrade. Picture quality hasn't improved since then, but viewers have simply become conditioned to it.
The inefficient compression is the issue, more than the resolution.

Lots of DVB-T-only receivers are still in use though, so they will probably maintain at least some service for a good while yet. SD-only receivers were still being widely sold until relatively recently.


  #102  
Old Yesterday, 12:46 PM posted to uk.tech.digital-tv
NY[_2_]
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Posts: 74
Default Predicting com7/8 SFN reception deterioration due to CCI

"Alex" wrote in message
...

"Indy Jess John" wrote in message
...

I also dislike the idea of throwing away perfectly serviceable equipment
just so that somebody can have the screen resolution to count the number
of twigs on a tree in winter.


Ordinarily I'd agree, but DVB-T was so bad, it was basically unfit for
purpose. When its original incarnation, in the form of OnDigital (later
ITV Digital) failed, many consumers cited poor picture quality as their
reason for rejecting it. The collapse of these services should have been
taken as an opportunity to upgrade. Picture quality hasn't improved since
then, but viewers have simply become conditioned to it.
The inefficient compression is the issue, more than the resolution.

Lots of DVB-T-only receivers are still in use though, so they will
probably maintain at least some service for a good while yet. SD-only
receivers were still being widely sold until relatively recently.


MPEG compression, as used for SD, does have the advantage that it is less
computationally intense to decode. Even a dedicated Sky box, let along my
reasonably fast PC, has trouble playing HD (or even sub-SD 544x576 broadcast
as T2 H264) smoothly at faster than normal speed, and there's a lot more
break up of the picture when you first start playing from a given point.

SD was better than it is now because they used higher bit rates. Some of the
earliest things I recorded from BBC and ITV in around 2010 were much bigger
files (in MB/hour) than nowadays, and the improved picture quality when
there is a lot of movement is very noticeable.

ITV1 really wound the bit rate down a year or so ago and things suffered.
Now they seem to have improved it a bit.

Terrestrial TV does have the big advantage for most people that it doesn't
require a new form of reception. The existing aerial would often work, at
least until they began using frequencies which were outside a given
transmitter's normal range, requiring a wideband aerial.

Satellite requires a brand new dish and new cabling to the various rooms. It
also suffers from the problem that it does not send all the channels down
the cable at the same time (*): you have to tune the LNB to a frequency and
polarity, which means you can't simply have a fan-out repeater as for
terrestrial. It's a shame that satellite was implemented as a large number
of small multiplexes rather than a smaller number of larger multiplexes: the
latter would at least increase the chances that two different channels that
you want to record would be on the same multiplex and so could be serviced
with a single receiver.


(*) With terrestrial, the same aerial cable gets broadcasts over the whole
UHF spectrum, and the receiver(s) on the ends of various fan-outs of that
aerial signal can choose any mux. With satellite they only map a small
section of the SHF spectrum (around 10-15 GHz IIRC) onto the 2 GHz (IIRC)
that is sent down the cable to the receiver, so you need a separate LNB and
cable for each mux that you want to receive simultaneously. That is a pain.

  #103  
Old Yesterday, 12:56 PM posted to uk.tech.digital-tv
Mark Carver
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Posts: 6,528
Default Predicting com7/8 SFN reception deterioration due to CCI

On 20/08/2019 11:46, Alex wrote:

"Indy Jess John" wrote in message ...

I also dislike the idea of throwing away perfectly serviceable equipment
just so that somebody can have the screen resolution to count the number
of twigs on a tree in winter.


Ordinarily I'd agree, but DVB-T was so bad, it was basically unfit for purpose.


There was nothing wrong (and still isn't) with DVB-T per se, it's just
that the first implementation in the UK used transmission power that was
far too weak for reliable reception for many. The picture quality was
(and still is) totally a function of bit rate selected for a particular
channel. Don't confuse break up due to reception corruption, with
artefacts due to bit rate starvation.
  #104  
Old Yesterday, 01:19 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,564
Default Predicting com7/8 SFN reception deterioration due to CCI

On 20/08/2019 12:46, NY wrote:

Satellite requires a brand new dish and new cabling to the various
rooms. It also suffers from the problem that it does not send all the
channels down the cable at the same time (*): you have to tune the LNB
to a frequency and polarity, which means you can't simply have a fan-out
repeater as for terrestrial. It's a shame that satellite was implemented
as a large number of small multiplexes rather than a smaller number of
larger multiplexes: the latter would at least increase the chances that
two different channels that you want to record would be on the same
multiplex and so could be serviced with a single receiver.


(*) With terrestrial, the same aerial cable gets broadcasts over the
whole UHF spectrum, and the receiver(s) on the ends of various fan-outs
of that aerial signal can choose any mux. With satellite they only map a
small section of the SHF spectrum (around 10-15 GHz IIRC) onto the 2 GHz
(IIRC) that is sent down the cable to the receiver, so you need a
separate LNB and cable for each mux that you want to receive
simultaneously. That is a pain.


In reality there's very little extra work in installing a quatro LNB and
a multiswitch. Obviously it costs more though. In poor terrestrial
reception areas a SAT IF system is by far the best solution.

Bill
  #105  
Old Yesterday, 02:03 PM posted to uk.tech.digital-tv
NY[_2_]
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Posts: 74
Default Predicting com7/8 SFN reception deterioration due to CCI

"Bill Wright" wrote in message
...
On 20/08/2019 12:46, NY wrote:

Satellite requires a brand new dish and new cabling to the various rooms.
It also suffers from the problem that it does not send all the channels
down the cable at the same time (*): you have to tune the LNB to a
frequency and polarity, which means you can't simply have a fan-out
repeater as for terrestrial. It's a shame that satellite was implemented
as a large number of small multiplexes rather than a smaller number of
larger multiplexes: the latter would at least increase the chances that
two different channels that you want to record would be on the same
multiplex and so could be serviced with a single receiver.


(*) With terrestrial, the same aerial cable gets broadcasts over the
whole UHF spectrum, and the receiver(s) on the ends of various fan-outs
of that aerial signal can choose any mux. With satellite they only map a
small section of the SHF spectrum (around 10-15 GHz IIRC) onto the 2 GHz
(IIRC) that is sent down the cable to the receiver, so you need a
separate LNB and cable for each mux that you want to receive
simultaneously. That is a pain.


In reality there's very little extra work in installing a quatro LNB and a
multiswitch. Obviously it costs more though. In poor terrestrial reception
areas a SAT IF system is by far the best solution.


The main problem is needing to run extra cables for the additional LNBs,
either through loft and down conduits (which may be full) or else long
outside of house and through additional holes in outside wall.

In our case we have an unusual arrangement installed by the previous owners
of the house: a wall plate with four coaxial leads protruding (no aerial or
F-connector sockets on wall with fly-leads to equipment). One of those is a
terrestrial feed from a distribution amplifier in the loft. The other three
"identical" leads have F connectors on the end.

However, on closer inspection (removing the wall plate) two of those F leads
come from a second distribution amplifier in the loft which is fed by one of
the two cables coming from the dish; the third lead is a totally separate
cable coming from the dish. I think the satellite distribution amplifier has
other cables going to other parts of the house, in the same way that the
terrestrial amplifier has feeds to other parts of the house. However I can't
find any other F-connector outlets elsewhere in the 0house...

I interpret this as two leads connected to one LNB (so both leads are always
tuned to the same frequency and polarisation) and one lead on the second LNB
(so that one can be tuned to a different frequency/polarisation).

I've labelled the separate feed so it is distinguishable from the other two
;-)

I'll have to get a second satellite receiver working to prove to myself that
both outputs on different LNBs really can be tuned to different multiplexes.


I'm lucky in that terrestrial seems to be good (despite Java Jive's
prediction of no reception!) although it only gets the lower frequency muxes
from Belmont - PSB1-3 and COM4, but not COM5 and 6, and not COM7 and 8
presumably because they are lower power). I suspect an old grouped aerial
and/or greater terrestrial attenuation because of a nearby hill that blocks
line of sight. In those circumstances, *any* terrestrial reception is a
bonus ;-)

For recording two simultaneous channels I need two sat LNBs (assuming
channels are not on same mux!) and SWMBO can probably manage with just
normal PSB1-3 channels on terrestrial.

Now I just need to get my Raspberry Pi that I use as PVR to recognise the
second satellite decoder: both are the same make and model but I think one
may be a newer revision with a chipset that isn't supported yet.

  #106  
Old Yesterday, 04:49 PM posted to uk.tech.digital-tv
Alex[_6_]
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Posts: 25
Default Predicting com7/8 SFN reception deterioration due to CCI


"Mark Carver" wrote in message ...

There was nothing wrong (and still isn't) with DVB-T per se, it's just
that the first implementation in the UK used transmission power that was
far too weak for reliable reception for many. The picture quality was
(and still is) totally a function of bit rate selected for a particular
channel. Don't confuse break up due to reception corruption, with
artefacts due to bit rate starvation.


Reception corruption and bit rate starvation look rather different, and I know how to distinguish between the two - I'm not quite that daft :-) But perhaps a few consumers didn't, so that may have accounted for some of the "poor picture quality" complaints.
You would need a very high MPEG2 bitrate to achieve near-transparency and approach the quality of a genuine PAL broadcast, far beyond anything DVB-T bandwidth costs could ever make economically viable.
Allocating main channels a slightly higher 'Mickey Mouse' bitrate; say, 4Mbit instead of 2Mbit, is just creating different shades of awful.

  #107  
Old Yesterday, 06:24 PM posted to uk.tech.digital-tv
NY[_2_]
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Posts: 74
Default Predicting com7/8 SFN reception deterioration due to CCI

"Alex" wrote in message
...

"Mark Carver" wrote in message
...

There was nothing wrong (and still isn't) with DVB-T per se, it's just
that the first implementation in the UK used transmission power that was
far too weak for reliable reception for many. The picture quality was
(and still is) totally a function of bit rate selected for a particular
channel. Don't confuse break up due to reception corruption, with
artefacts due to bit rate starvation.


Reception corruption and bit rate starvation look rather different, and I
know how to distinguish between the two - I'm not quite that daft :-) But
perhaps a few consumers didn't, so that may have accounted for some of the
"poor picture quality" complaints.
You would need a very high MPEG2 bitrate to achieve near-transparency and
approach the quality of a genuine PAL broadcast, far beyond anything DVB-T
bandwidth costs could ever make economically viable.
Allocating main channels a slightly higher 'Mickey Mouse' bitrate; say,
4Mbit instead of 2Mbit, is just creating different shades of awful.


On the other hand, which is worse: SD digital broadcast with a typical BBC
One bitrate, or analogue PAL with no noise or ghosting but with the normal
PAL artefacts?

I much prefer digital (apart from when there is a lot of movement and I look
at single frames) because the picture is free of coloured fringes on
vertical edges (especially captions). It is also sharper. It is very easy to
distinguish between archive material that was generated using a digital
workflow and material which has a PAL footprint on it. I wouldn't class 4
Mbps as "awful". It's only when you get down to the 1 Mbps rate that ITV1
used to use a couple fo years ago that things start to look a bit iffy, and
for true "awful" you need to descend to the sub-SD 544x576 very bit-starved
channels like Yesterday and Drama - and even that isn't too noticeable if
you are engrossed in the story and aren't looking critically at picture
quality.

HD is much better, for not much increase in bitrate despite having about 5x
the total number of pixels per frame. That's the beauty of the more
efficient H264 compression. It would be interesting to see SD (720x576)
versions of the same channel by both MPEG and H264 at the same bitrate, and
then to see H264 reduced to a level that gives a picture which is
subjectively similar to the MPEG version - I imagine that will happen at a
significantly lower bitrate for H264 than for MPEG.

  #108  
Old Yesterday, 06:45 PM posted to uk.tech.digital-tv
Alex[_6_]
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Posts: 25
Default Predicting com7/8 SFN reception deterioration due to CCI


"NY" wrote in message ...

On the other hand, which is worse: SD digital broadcast with a typical BBC
One bitrate, or analogue PAL with no noise or ghosting but with the normal
PAL artefacts?


PAL on a decent CRT any day for me, but when the two (DVB-T and PAL) were simulcast together, the latter was of course derived from a digital feed, so with artefacts of reduced colour depth, deinterlacing, aspect ratio conversion, horizontal bandwidth reduction, etcetera, making an objective side-by-side comparison impossible.


I much prefer digital (apart from when there is a lot of movement and I look
at single frames) because the picture is free of coloured fringes on
vertical edges (especially captions). It is also sharper.


It isn't sharper - quite the opposite! But you get used to the artefacts of whichever system you've been watching for a while I suppose.

It is very easy to distinguish between archive material that was generated using a digital
workflow and material which has a PAL footprint on it.


Depends on the channel. The BBC seem to be expert at making SD PAL sources look bloody awful - washed out colours and approx 540x576 playout resolution (even when upscaled on an HD channel). Channel 5 HD do a much better job.
Also the two don't mix well - analogue noise on a PAL recording consumes MPEG bandwidth, creating more artefacts, PAL colour footprint becomes more noticible when digitally quantised and compressed, etc.

  #109  
Old Yesterday, 08:53 PM posted to uk.tech.digital-tv
NY[_2_]
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Posts: 74
Default Predicting com7/8 SFN reception deterioration due to CCI

"Alex" wrote in message
...
Also the two don't mix well - analogue noise on a PAL recording consumes
MPEG bandwidth, creating more artefacts


Or requiring more bandwidth. I have a recording of Abigail's Party (made on
PAL equipment) that BBC Four repeated a few years ago. The file is 4.5 GB
for 100 minutes, so about 45 MB/min, whereas a typical sourced-on-digital
modern programme on BBC 1 (using an episode of Gentleman Jack, earlier this
year, as a test) is about 1.3 GB for 60 mins, so about 22 MB/min. ITV
(episode of Endeavour from earlier this year) is about 1.2 GB for 90 mins,
so 13 MB/min. All those were recorded as SD (MPEG) from terrestrial TV
rather than satellite.

I imagine the extra tape noise and analogue signal processing noise, and the
PAL footprint, in Abigail's Party meant that greater bandwidth was needed to
give good picture quality, and the BBC's statistical multiplexing was
tweaked to allow that to happen on this occasion.

 




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