I took courses in colour TV during the middle to late sixties.
I understood Walter Bruch's PAL system and our 625 line variant.

But I honestly never troubled to find out how our digital TV system works.

Can someone point me to a sort of "UK Digital TV for geriatrics" that might be helpful?

TIA, Alan

--
Mint 20.3, kernel 5.4.0-124-generic, Cinnamon 5.2.7
running on an AMD Phenom II X4 Black edition processor with 16GB of DRAM.

On Sat 29/10/2022 18:54, pinnerite wrote:
> I took courses in colour TV during the middle to late sixties.
> I understood Walter Bruch's PAL system and our 625 line variant.
>
> But I honestly never troubled to find out how our digital TV system works.
>
> Can someone point me to a sort of "UK Digital TV for geriatrics" that might be helpful?
>
> TIA, Alan
>
>
>

Google the usual best bet - DVB for Dummies? (DVB is the technical name
for UK DTTV.) If that spurs you on and you want to research HD then its
DVB-T2.

In article <tjjqfd$3k5oe$1@dont-email.me>,
Woody <harrogate3@ntlworld.com> wrote:

> Google the usual best bet - DVB for Dummies? (DVB is the technical
> name for UK DTTV.)

Yes.

> If that spurs you on and you want to research
> HD then its DVB-T2.

Not really.

The connection between T2 and HD is a political decision there is no
technical link. You can transmit HD on DVB-T without issue, I know,
I'm doing it.

Bob.

"Bob Latham" <bob@sick-of-spam.invalid> wrote in message
news:5a3f21cdbabob@sick-of-spam.invalid...
> The connection between T2 and HD is a political decision there is no
> technical link. You can transmit HD on DVB-T without issue, I know,
> I'm doing it.

And conversely T2 can be (and is) used for sub-SD channels - ie 544x576
rather than 720x576. PSB3 has 5Select and TBN, and COM7 and COM8 used to
have some sub-SD channels. In fact all the T2 multiplexes had a mixture of
HD and sub-SD but no "full" SD.

It's the same as DVDs can have HD content and BluRays can have SD content.
Software players such as VLC will happily play a DVD with HD content (if you
burn the DVD yourself) though I wonder if a dedicated BluRay (and DVD)
player will play it.

"Woody" <harrogate3@ntlworld.com> wrote in message
news:tjjqfd$3k5oe$1@dont-email.me...
> On Sat 29/10/2022 18:54, pinnerite wrote:
>> I took courses in colour TV during the middle to late sixties.
>> I understood Walter Bruch's PAL system and our 625 line variant.
>>
>> But I honestly never troubled to find out how our digital TV system
>> works.
>>
>> Can someone point me to a sort of "UK Digital TV for geriatrics" that
>> might be helpful?
>
> Google the usual best bet - DVB for Dummies? (DVB is the technical name
> for UK DTTV.) If that spurs you on and you want to research HD then its
> DVB-T2.

If you have the ability to record a DVB data stream to a PC file (eg using
NextPVR, TVHeadend or VLC and a DVB-USB tuner), and you are really
fascinated by the technicalities of DVB, I can recommend a free utility
called TSReaderLite (Windows only). This is a cut-down version of a version
that costs money.

It shows you all the various tables in the DVB stream which a TV uses when
it does its initial tune/scan and then saves the information to its local
memory so when you ask for BBC1 the TV knows which frequency to tune to, and
the stream IDs for video, programme sound, audio description sound,
subtitles. There's also TVCapture, made by the same company that makes
NextPVR, which can record a 1-minute sample of any DVB multiplex - so you
get all the channels that are contained in the mux. VLC (Media | OPen
Capture Device, Capture mode=TV-digital, Transponder/mux frequency=482,000
(kHz) can tune to any mux (if you have a tuner) and can then record the
whole mux indefinitely. (Substitute one of your correct mux frequencies
where I've written 482,000).

One thing to be aware of: digital SD uses 720x576 because these numbers are
compatible with 625-line analogue TV, which had 575 lines of picture (the
rest was sync pulses) and the bandwidth gave a horizontal resolution (for an
old 4:3 frame) of about 720 pixels - ie it could just resolve 720 alternate
black and white lines. The reason that UK digital TV uses UHF channels which
are 8 MHz apart is that analogue needed 6 MHz to transmit *a single TV
station* and a bit of extra bandwidth was allowed (hence 8 rather than 6 MHz
spacing).

On Sat 29/10/2022 20:59, Bob Latham wrote:
> In article <tjjqfd$3k5oe$1@dont-email.me>,
> Woody <harrogate3@ntlworld.com> wrote:
>
>> Google the usual best bet - DVB for Dummies? (DVB is the technical
>> name for UK DTTV.)
>
> Yes.
>
>> If that spurs you on and you want to research
>> HD then its DVB-T2.
>
> Not really.
>
> The connection between T2 and HD is a political decision there is no
> technical link. You can transmit HD on DVB-T without issue, I know,
> I'm doing it.
>

I am talkjng here about the UK situation. I don't dispute that there are
other possibilities but I am replying - hence the insertion of UK -
about how we use it here!!

There are two things here. The first is how do the cameras create the colour
signal, ie is it completely digital from the ccd in the camera, then encoded
in your format of choice, or did or do we have a system where the old
fashioned are converted into the pixels etc later on.Similarly at the
receiving end, since there appear to be no lines as such, is the actual
screen merely created by the software that decompresses and scales the
incoming signal once its been de multiplexed to the channel you want to look
at. You hear of lots of snazzy named video processing in different
companies TV implementation, and all of one assumes are there to attempt to
make lossy compression look less bad. I guess this was analogous to the
different ways audio was encoded on tape to remove his and distortion. DBX
won hands down, but it was not the winner in the format wars, Dolby was. I
do obviously remember all the different video tape formats and later on they
started to use special processing to mask the deficiencies of the medium.
As I have never seen up to data TVs, I do not know how successful these
enhancements are, but there are usually custom video clips made to really
embarrassed them.
Brian

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"Bob Latham" <bob@sick-of-spam.invalid> wrote in message
news:5a3f21cdbabob@sick-of-spam.invalid...
> In article <tjjqfd$3k5oe$1@dont-email.me>,
> Woody <harrogate3@ntlworld.com> wrote:
>
>> Google the usual best bet - DVB for Dummies? (DVB is the technical
>> name for UK DTTV.)
>
> Yes.
>
>> If that spurs you on and you want to research
>> HD then its DVB-T2.
>
> Not really.
>
> The connection between T2 and HD is a political decision there is no
> technical link. You can transmit HD on DVB-T without issue, I know,
> I'm doing it.
>
> Bob.
>

The answer to your last question seems to be sometimes. Once again its
outside the standard and the decision,one assumes of the person making the
chips and their software. I've never quite understood why they put in
artificial restrictions.
Brian

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"NY" <me@privacy.invalid> wrote in message
news:tjk2da$3m2k2$1@dont-email.me...
> "Bob Latham" <bob@sick-of-spam.invalid> wrote in message
> news:5a3f21cdbabob@sick-of-spam.invalid...
>> The connection between T2 and HD is a political decision there is no
>> technical link. You can transmit HD on DVB-T without issue, I know,
>> I'm doing it.
>
> And conversely T2 can be (and is) used for sub-SD channels - ie 544x576
> rather than 720x576. PSB3 has 5Select and TBN, and COM7 and COM8 used to
> have some sub-SD channels. In fact all the T2 multiplexes had a mixture of
> HD and sub-SD but no "full" SD.
>
> It's the same as DVDs can have HD content and BluRays can have SD content.
> Software players such as VLC will happily play a DVD with HD content (if
> you burn the DVD yourself) though I wonder if a dedicated BluRay (and DVD)
> player will play it.

If you go back to analogue, although the start and end bits were similar the
bits in between could be wildly different. NTSC of course had very little
error correction for phase problems. Pal and Secam had by reversing phases
and ending up with something closer to what was required. they both also
used colour of much less definition than the monochrome image and hence you
could get colour bleed over at times. Even transmission was different around
the world, some had positive going video, some negative some have very
different sound and vision spacing, UK was in the middle, and some used AM
and Secam, Hello France and some negative mod secam and fm sound Eastern
Europe.

Brian

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"Woody" <harrogate3@ntlworld.com> wrote in message
news:tjkbbu$3o5oa$1@dont-email.me...
> On Sat 29/10/2022 20:59, Bob Latham wrote:
>> In article <tjjqfd$3k5oe$1@dont-email.me>,
>> Woody <harrogate3@ntlworld.com> wrote:
>>
>>> Google the usual best bet - DVB for Dummies? (DVB is the technical
>>> name for UK DTTV.)
>>
>> Yes.
>>
>>> If that spurs you on and you want to research
>>> HD then its DVB-T2.
>>
>> Not really.
>>
>> The connection between T2 and HD is a political decision there is no
>> technical link. You can transmit HD on DVB-T without issue, I know,
>> I'm doing it.
>>
>
> I am talkjng here about the UK situation. I don't dispute that there are
> other possibilities but I am replying - hence the insertion of UK - about
> how we use it here!!
>

Yes I never quite understood Nicam which seemed to have a very short life
cycle, coming as it did just before full digital. To be honest my mind tells
me that nicam sound actually sounded better than the current sound which
seems to be plagued with leaden audio, which sounds like a wider band
version of some telephone codecs.
Brick wall filtering and lack of dynamics.
I often wondered what might happen to a multiplex if every channel put out
screens of totally random white noise on the video. I'd imagine it would all
go very blocky. These compression systems to get more channels into less
space are after all, a compromise.
Brian

--

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Note this Signature is meaningless.!
"NY" <me@privacy.invalid> wrote in message
news:tjk3ea$3mab2$1@dont-email.me...
> "Woody" <harrogate3@ntlworld.com> wrote in message
> news:tjjqfd$3k5oe$1@dont-email.me...
>> On Sat 29/10/2022 18:54, pinnerite wrote:
>>> I took courses in colour TV during the middle to late sixties.
>>> I understood Walter Bruch's PAL system and our 625 line variant.
>>>
>>> But I honestly never troubled to find out how our digital TV system
>>> works.
>>>
>>> Can someone point me to a sort of "UK Digital TV for geriatrics" that
>>> might be helpful?
>>
>> Google the usual best bet - DVB for Dummies? (DVB is the technical name
>> for UK DTTV.) If that spurs you on and you want to research HD then its
>> DVB-T2.
>
> If you have the ability to record a DVB data stream to a PC file (eg using
> NextPVR, TVHeadend or VLC and a DVB-USB tuner), and you are really
> fascinated by the technicalities of DVB, I can recommend a free utility
> called TSReaderLite (Windows only). This is a cut-down version of a
> version that costs money.
>
> It shows you all the various tables in the DVB stream which a TV uses when
> it does its initial tune/scan and then saves the information to its local
> memory so when you ask for BBC1 the TV knows which frequency to tune to,
> and the stream IDs for video, programme sound, audio description sound,
> subtitles. There's also TVCapture, made by the same company that makes
> NextPVR, which can record a 1-minute sample of any DVB multiplex - so you
> get all the channels that are contained in the mux. VLC (Media | OPen
> Capture Device, Capture mode=TV-digital, Transponder/mux frequency=482,000
> (kHz) can tune to any mux (if you have a tuner) and can then record the
> whole mux indefinitely. (Substitute one of your correct mux frequencies
> where I've written 482,000).
>
>
> One thing to be aware of: digital SD uses 720x576 because these numbers
> are compatible with 625-line analogue TV, which had 575 lines of picture
> (the rest was sync pulses) and the bandwidth gave a horizontal resolution
> (for an old 4:3 frame) of about 720 pixels - ie it could just resolve 720
> alternate black and white lines. The reason that UK digital TV uses UHF
> channels which are 8 MHz apart is that analogue needed 6 MHz to transmit
> *a single TV station* and a bit of extra bandwidth was allowed (hence 8
> rather than 6 MHz spacing).

"Brian Gaff" <brian1gaff@gmail.com> wrote in message
news:tjlh2u$3a0s$1@dont-email.me...
> Yes I never quite understood Nicam which seemed to have a very short life
> cycle, coming as it did just before full digital. To be honest my mind
> tells me that nicam sound actually sounded better than the current sound
> which seems to be plagued with leaden audio, which sounds like a wider
> band version of some telephone codecs.
> Brick wall filtering and lack of dynamics.
> I often wondered what might happen to a multiplex if every channel put
> out screens of totally random white noise on the video. I'd imagine it
> would all go very blocky. These compression systems to get more channels
> into less space are after all, a compromise.

That's a good point about statistical multiplexing: it allocates a variable
bit rate to each station in the mux according to what it needs to retain
good quality. The hope is that at times when BBC 1 needs a higher bit rate
to reproduce lots of detail and motion (which doesn't compress well), BBC 2,
3 and 4 might happen not to need as much. I imagine that during coverage of
the Queen's death, lying-in-state and funeral, broadcasters had to take care
not to exceed the total bandwidth of a mux (or hit its brickwall maximum
bandwidth, affecting quality) at times when several channels in the mux were
showing identical pictures, no the normal rules of statistical multiplexing
didn't apply.

On 30/10/2022 10:26, NY wrote:
> That's a good point about statistical multiplexing: it allocates a variable
> bit rate to each station in the mux according to what it needs to retain
> good quality. The hope is that at times when BBC 1 needs a higher bit rate
> to reproduce lots of detail and motion (which doesn't compress well), BBC 2,
> 3 and 4 might happen not to need as much. I imagine that during coverage of
> the Queen's death, lying-in-state and funeral, broadcasters had to take care
> not to exceed the total bandwidth of a mux (or hit its brickwall maximum
> bandwidth, affecting quality) at times when several channels in the mux were
> showing identical pictures, no the normal rules of statistical multiplexing
> didn't apply.

Wasn't there potentially a similarly problem in analogue days when all
the Senders at the big Short Wave sites were transmitting the Queen's
Speech at the same time. It would have played havoc with the National
Grid if all exactly synchronised so they added small delays so not
synchronised.

"Brian Gaff" <brian1gaff@gmail.com> wrote in message
news:tjlh2u$3a0s$1@dont-email.me...
> Yes I never quite understood Nicam which seemed to have a very short life
> cycle, coming as it did just before full digital. To be honest my mind
> tells me that nicam sound actually sounded better than the current sound
> which seems to be plagued with leaden audio, which sounds like a wider
> band version of some telephone codecs.

My gut feeling was that NICAM sounded better than MPEG, especially on the
lower-budget channels which use 128 kbits/sec rather than 192 or 224
kbits/sec. I wonder if a digital system could have been devised that used a
NICAM-like sound stream, to give the greater dynamic range.

Another issue that hasn't been mentioned is interlacing. This was essential
in the days of CRT TVs to reduce the perceived flicker without doubling the
frame rate. Now that (almost) all TVs have LED screens, where each pixel can
be lit, simultaneously, for the full 1/25 of a frame period, interlacing is
irrelevant.

Do modern TV cameras actually scan the frame interlaced (ie all the odd rows
followed by all the even rows) or do they scan progressively (rows 1, 2, 3,
4 etc)? In other words, do you still get two fields that are exposed 1/50
second apart, with movement between the fields, or are all the pixels
exposed simultaneously, with no movement between the odd and even fields?
The movement or lack of movement was one of the biggest ways of
distinguishing between film and video in the days when most drama was film
exteriors and studio video interiors. Obviously another giveaway was the
grain and muddy colours of film, versus no grain, vibrant (over-vibrant! *)
colours and comet-tails on highlights ;-)

(*) I remember a shot-on-location-on-video production of As You Like It, in
the late 1970s when I was studying it for O level Eng Lit, and a newspaper
reviewer derided the "holiday brochure unsubtle colours".

On 30/10/2022 09:45, Brian Gaff wrote:
> Yes I never quite understood Nicam which seemed to have a very short life
> cycle, coming as it did just before full digital. To be honest my mind tells
> me that nicam sound actually sounded better than the current sound which
> seems to be plagued with leaden audio, which sounds like a wider band
> version of some telephone codecs.

NICAM-728 was used for nearly twenty years I think and only ended with
Digital Switch Over.

On 30/10/2022 10:50, MB wrote:
> On 30/10/2022 09:45, Brian Gaff wrote:
>> Yes I never quite understood Nicam which seemed to have a very short
>> life
>> cycle, coming as it did just before full digital. To be honest my
>> mind tells
>> me that nicam sound actually sounded better than the current sound which
>> seems to be plagued with  leaden audio, which sounds like a wider band
>> version of some telephone codecs.
>
>
> NICAM-728 was used for nearly twenty years I think and only ended with
> Digital Switch Over.
>
>
>
NICAM was used internally by the Beeb from the early 80s (it replaced
the linear PCM streams on their national radio distribution)

It formed the 'guts' of what became the broadcast to the home 728 kb/s
system (Which in some areas lasted 25 years)

On 30/10/2022 09:25, Brian Gaff wrote:
> The first is how do the cameras create the colour
> signal, ie is it completely digital from the ccd in the camera, then encoded
> in your format of choice, or did or do we have a system where the old
> fashioned are converted into the pixels etc later on.

You are confusing sampling with digital, and furthermore, you are
specifying a specific technology which is a sampled analogue one. CCD
definitely reads out a sequence of analogue values that correspond to
pixels. I suppose the A/D convertor may be on the same chip, so the
analogue signal might not leave the chip.

I'm sure CMOS does the same, except that it is not physically
constrained to reading out lines sequentially.

> Similarly at the
> receiving end, since there appear to be no lines as such, is the actual
> screen merely created by the software that decompresses and scales the
> incoming signal once its been de multiplexed to the channel you want to look
> at.

There are lines on the screen, but there are negligible gaps between
them, so you need to get out a magnifying glass to see them. The images
are also rectangular arrays of pixels, so there are lines in the image
as well. A specialised IC will interpolate the images pixels to fit the
display ones, e.g. "scaler" in the diagram in this 2014 article:
<https://www.electronicproducts.com/system-block-diagram-for-atsc-digital-tv/>.

On 30/10/2022 10:39, NY wrote:
>
> Another issue that hasn't been mentioned is interlacing. This was
> essential in the days of CRT TVs to reduce the perceived flicker without
> doubling the frame rate. Now that (almost) all TVs have LED screens,
> where each pixel can be lit, simultaneously, for the full 1/25 of a
> frame period, interlacing is irrelevant.

So called LED TVs are actually LED (as against cold cathode) backlit LCD
ones.

Setting the image on the screen does involve scanning, even if it
doesn't decay significantly between scans.

I believe interlacing is desirable for sports, as the ball's position is
updated more often.

On Sun, 30 Oct 2022 10:39:34 -0000, "NY" <me@privacy.invalid> wrote:

>Do modern TV cameras actually scan the frame interlaced (ie all the odd rows
>followed by all the even rows) or do they scan progressively (rows 1, 2, 3,
>4 etc)? In other words, do you still get two fields that are exposed 1/50
>second apart, with movement between the fields, or are all the pixels
>exposed simultaneously, with no movement between the odd and even fields?

The last time I worked with broadcast cameras was some years ago, but
I remember them being switchable between the two modes, so the answer
would be "it depends".

Rod.

NICAM isn't 'lossy' in the same way as modern codecs. It just tends to
generate a dither noise level rather than guess what it can leave out from
the sound pattern that won't be missed.

In article <tjlh2u$3a0s$1@dont-email.me>, Brian Gaff
<brian1gaff@gmail.com> wrote:
> Yes I never quite understood Nicam which seemed to have a very short
> life cycle, coming as it did just before full digital. To be honest my
> mind tells me that nicam sound actually sounded better than the current
> sound which seems to be plagued with leaden audio, which sounds like a
> wider band version of some telephone codecs. Brick wall filtering and
> lack of dynamics. I often wondered what might happen to a multiplex if
> every channel put out screens of totally random white noise on the
> video. I'd imagine it would all go very blocky. These compression
> systems to get more channels into less space are after all, a
> compromise. Brian

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article <20221029185426.f45b47e35be4196c0e590d50@gmail.com>,
pinnerite
<pinnerite@gmail.com> wrote:
> I took courses in colour TV during the middle to late sixties. I
> understood Walter Bruch's PAL system and our 625 line variant.

> But I honestly never troubled to find out how our digital TV system
> works.

> Can someone point me to a sort of "UK Digital TV for geriatrics" that
> might be helpful?

> TIA, Alan

Try books by John Watkinson.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

In article <tjk3ea$3mab2$1@dont-email.me>, NY <me@privacy.invalid> wrote:
> If you have the ability to record a DVB data stream to a PC file (eg
> using NextPVR, TVHeadend or VLC and a DVB-USB tuner), and you are
> really fascinated by the technicalities of DVB, I can recommend a free
> utility called TSReaderLite (Windows only). This is a cut-down version
> of a version that costs money.

FWIW VLC will also record station streams if you wish that, and shows the
programme as it goes. Quite handy as a recorder.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
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Audio Misc http://www.audiomisc.co.uk/index.html

David Woolley wrote:

> So called LED TVs are actually LED (as against cold cathode) backlit LCD ones.

Apart from OLED TVs.

Yes I have problems with diagrams for obvious reasons. As for your input
analogy, I was trying to figure out when things are changing, IE could it
be possible to effectively have a pixel level connection, so that there is
no overall screen refresh.
Brian

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"David Woolley" <david@ex.djwhome.demon.invalid> wrote in message
news:tjlmn8$4j3r$1@dont-email.me...
> On 30/10/2022 09:25, Brian Gaff wrote:
>> The first is how do the cameras create the colour
>> signal, ie is it completely digital from the ccd in the camera, then
>> encoded
>> in your format of choice, or did or do we have a system where the old
>> fashioned are converted into the pixels etc later on.
>
> You are confusing sampling with digital, and furthermore, you are
> specifying a specific technology which is a sampled analogue one. CCD
> definitely reads out a sequence of analogue values that correspond to
> pixels. I suppose the A/D convertor may be on the same chip, so the
> analogue signal might not leave the chip.
>
> I'm sure CMOS does the same, except that it is not physically constrained
> to reading out lines sequentially.
>
>> Similarly at the receiving end, since there appear to be no lines as
>> such, is the actual screen merely created by the software that
>> decompresses and scales the incoming signal once its been de multiplexed
>> to the channel you want to look at.
>
> There are lines on the screen, but there are negligible gaps between them,
> so you need to get out a magnifying glass to see them. The images are
> also rectangular arrays of pixels, so there are lines in the image as
> well. A specialised IC will interpolate the images pixels to fit the
> display ones, e.g. "scaler" in the diagram in this 2014 article:
> <https://www.electronicproducts.com/system-block-diagram-for-atsc-digital-tv/>.

Not only that but the of stages of tuners were and maybe still are affected
by the adjacent channel being strong, either desensing the set or
intermodulation effects in the rf stages. Obviously they tried not to use
Adjacent channels, but often you could get another region almost as strongly
as yours. Brian

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"NY" <me@privacy.invalid> wrote in message
news:tjk3ea$3mab2$1@dont-email.me...
> "Woody" <harrogate3@ntlworld.com> wrote in message
> news:tjjqfd$3k5oe$1@dont-email.me...
>> On Sat 29/10/2022 18:54, pinnerite wrote:
>>> I took courses in colour TV during the middle to late sixties.
>>> I understood Walter Bruch's PAL system and our 625 line variant.
>>>
>>> But I honestly never troubled to find out how our digital TV system
>>> works.
>>>
>>> Can someone point me to a sort of "UK Digital TV for geriatrics" that
>>> might be helpful?
>>
>> Google the usual best bet - DVB for Dummies? (DVB is the technical name
>> for UK DTTV.) If that spurs you on and you want to research HD then its
>> DVB-T2.
>
> If you have the ability to record a DVB data stream to a PC file (eg using
> NextPVR, TVHeadend or VLC and a DVB-USB tuner), and you are really
> fascinated by the technicalities of DVB, I can recommend a free utility
> called TSReaderLite (Windows only). This is a cut-down version of a
> version that costs money.
>
> It shows you all the various tables in the DVB stream which a TV uses when
> it does its initial tune/scan and then saves the information to its local
> memory so when you ask for BBC1 the TV knows which frequency to tune to,
> and the stream IDs for video, programme sound, audio description sound,
> subtitles. There's also TVCapture, made by the same company that makes
> NextPVR, which can record a 1-minute sample of any DVB multiplex - so you
> get all the channels that are contained in the mux. VLC (Media | OPen
> Capture Device, Capture mode=TV-digital, Transponder/mux frequency=482,000
> (kHz) can tune to any mux (if you have a tuner) and can then record the
> whole mux indefinitely. (Substitute one of your correct mux frequencies
> where I've written 482,000).
>
>
> One thing to be aware of: digital SD uses 720x576 because these numbers
> are compatible with 625-line analogue TV, which had 575 lines of picture
> (the rest was sync pulses) and the bandwidth gave a horizontal resolution
> (for an old 4:3 frame) of about 720 pixels - ie it could just resolve 720
> alternate black and white lines. The reason that UK digital TV uses UHF
> channels which are 8 MHz apart is that analogue needed 6 MHz to transmit
> *a single TV station* and a bit of extra bandwidth was allowed (hence 8
> rather than 6 MHz spacing).

Hang on though, most am stations tended to be on the same frequency, and
they had no echo so you could get phase effects, but not echo. Nowadays
however nobody bothers on am to make sure all the stations on the same
frequency are synchronised at all resulting in a togl echo mess most of the
time after dark.

Brian

--

--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"MB" <MB@nospam.net> wrote in message news:tjlk77$3v90$1@dont-email.me...
> On 30/10/2022 10:26, NY wrote:
>> That's a good point about statistical multiplexing: it allocates a
>> variable
>> bit rate to each station in the mux according to what it needs to retain
>> good quality. The hope is that at times when BBC 1 needs a higher bit
>> rate
>> to reproduce lots of detail and motion (which doesn't compress well), BBC
>> 2,
>> 3 and 4 might happen not to need as much. I imagine that during coverage
>> of
>> the Queen's death, lying-in-state and funeral, broadcasters had to take
>> care
>> not to exceed the total bandwidth of a mux (or hit its brickwall maximum
>> bandwidth, affecting quality) at times when several channels in the mux
>> were
>> showing identical pictures, no the normal rules of statistical
>> multiplexing
>> didn't apply.
>
>
> Wasn't there potentially a similarly problem in analogue days when all the
> Senders at the big Short Wave sites were transmitting the Queen's Speech
> at the same time. It would have played havoc with the National Grid if
> all exactly synchronised so they added small delays so not synchronised.
>
>
>