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Is there anything that the rapist John Bunt isn't an expert on?

www.surfbaud.org

GF's little place on the web
High Definition – or not?
Monday, November 2, 2009 at 2:34 pm

As regular readers of the old blog will recall, some time ago I went out
and bought a top of the range 46" Samsung Series 7 RGB LED backlight LCD
screen / monitor / telly.

Currently it is sat in my mother's house, it was initially connected to
the bog standard Virgin TV package, but the picture was so awful
(compared to what the 1080p screen is capable of displaying) that I
upgraded her to the Virgin HD package.

Only a few of the channels on Virgin HD are broadcast in "HD", the rest
are up-sampled to 1920 x 1080 by the HD box, and of the few channels
that are in HD, I honestly cannot tell if they are up-sampled 720i or
1080i, the picture quality is so awful.

Now remember, I have run this screen off my own created 1080p material,
shot on a 1080p HD video camera, so I *know* what the screen is capable of.

The fact is, saying 480i or 720i or 720p or 1080i or 1080p doesn't
actually tell you anything except the resolution the picture is actually
displayed in, it does not tell you a damn thing about the actual
resolution of the picture itself, nor the amount of information used to
refresh that picture for the next frame in the sequence of video.

That metric is actually measured in bandwidth.

Many of you will be familiar with mp3 format music, so let me give you
an audio analogy.

The various formats such as 480i, 720p, 1080i, you can think of, in
audio terms, as mono, stereo, quadrophonic, 5.1 surround, etc etc.

What Virgin, and everyone else, are doing is this.

"Mono is crap, you need stereo at least, and ideally 5.1 surround,
upgrade and buy this product!"

So, people go out and buy a 5.1 surround sound system, it may be crap,
or it may be actually capable of exceeding the audio spec.




They plug this new system into Virgin / Sky / Freesat / whatever, and lo
and behold, they get different noises out of different speakers, and it
does, subjectively, sound better.

But, in audio terms, they have gone from 64 kBit mono to 92 kBit 5.1,
(we are talking bandwidth here) so it only sounds better subjectively.

You have gone from 1 channel using 64 kBit, to 5 channels sharing 92
kBit, or about 20 kBit per channel, when you should have had 5 x 64
320 kBit to get the SAME SOUND QUALITY on each channel as you had in 64
kBit mono.

The fact is, to get anything even approaching half decent 5.1 surround
sound, 92 kBit simply is not enough, you need 256 KBit as a minimum, 320
kBit is starting to get somewhere.

It is the same with "HD" video, you need about 25 MBit/sec to really
carry all the information that a 1080p display can use, but in practical
terms 15 MBit/sec is enough to fool everyone except the expert that you
are in fact getting the full bandwidth, a bit like only real audiophiles
can tell the difference between 192 kBit mp3 and a full audio CD sound.

So what do we get when watching Virgin HD?

It varies, thanks to variable compression and the marketing requirement
to get 150 channels of time shifted, repeat, crap programming into the
bandwidth available for 20 decent HD channels, and annoyingly, and
deliberately, the HD channels are stuffed with stuff that does not
actually show HD off, because after all, you can't have paying customers
going from an HD channel in your package to a normal channel, and
noticing a truly crap picture by comparison.

So, in reality, we get between 2 and 4 Mbit/sec when watching the 1920 x
1080 "HD" output of the Virgin HD service, which is like listening to 92
kBit audio in 5.1, and it gets even worse if you have a decent screen,
because it is then like listening to 92 kBit 5.1 audio on a state of the
art 5.1 audio system, it is little short of torture, there are as many
artifacts (artificial bits of data created by the decompression and
up-sampling processes) as there are bits of signal.

I have spent the past day researching this, and, at least here in the
UK, no broadcaster publishes the bandwidth of any of their channels, and
of course no broadcaster publishes a minimum bandwidth for any channel.

In my own experimentation (and I did many practical experiments to
determine this) the point at which a 1080p picture became degraded
enough to be actually noticeable while watching was around the 12
Mbit/sec mark, so that forms a useful metric.

(Please, please, please, do not point me at all the people on various AV
forums who think the picture quality they get is excellent, not one of
them has ever seen true 1080p @ 15 MBit/sec +)

Sadly, in consumer-land this means marketing droids either dividing the
number of channels available by 7 (no big deal, dump the shopping
channels, and all the +1 hour dupe channels, and you just divided by 3
anyway) or the bean counters shelling out for an infrastructure capable
of 7 times the bandwidth.

Part of the problem here is that NOBODY in any of the standards bodies
decided to bother with anything except picture resolution, and the
number of frames per second, NOBODY paid even the slightest bit of
attention to bandwidth, with the result that while the full studio
recording bandwidth of 1080p can be as high as 3 Gbit/sec (uncompressed)
or more normally 60 Mbit/sec, what used to be known as "broadcast
quality" e.g. the signal quality actually sent TO the transmitters, when
it comes to the consumer actually receiving this "HD" signal in their
homes, 2 Mbit/sec still is not too puny to legally qualify as "HD".

Oh, and your gold plated 50 quid HDMI cable rated at 1.5 Gbit/sec really
isn't going to make any difference when the decoder box only has 2 to 4
Mbit/sec going in.

When will this state of affairs change?

Obviously not for MANY years, if left to commercial sources alone.

So my advice is sure, buy a 1080p set if you plan on connecting it to a
PC, to a games box capable of 1080p, or to a Blu-ray or HD-DVD player,
or a 1080p HD video camera.

DO NOT EVER connect any television service, of any kind, to a 1080p set.

Instead, buy a FAR cheaper 720i / 720p set to connect to the television
service, and unless your viewing room is 30 feet long, stick to
something 32" or smaller.

Virgin is being binned from my mother's, a one off spend of £150 on a
FreesatHD install will give higher bandwidth per channel and no
until-you-die monthly expenditure.

Peace.

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