Re: examples of digital rip-off

[Bruce]

I don't think I have ever seen you in my living room or bedroom, so probably not!

But you never know. ;-)

[Bruce]

Perhaps people wish to have a general discussion about digital TV rather than labour the point about Crystal Palace - a point that has already been made again, and again ...

And here are you, wanting to make it again. ;-)

[Bruce]

And they will affect analogue just as much as digital. ;-)

[tony sayer]

Neither is your statement dontcha tink;?..

Analogue radio on FM can be very good indeed given a clean signal and decent aerial. Digital radio which is horribly mangled by MP2 bit rate compression sounds worse..

However signals off satellite like Bayern Klassik 4 are excellent and are what digital radio should be at 334 odd K/Bits for the audio:)..

Analogue TV especially on a good clean signal with a set thats got a well designed PAL decoder will show up all what's wrong with the current implementation of T-DTV in the UK which is far too many channels compressed into the bandwidth available.

Digital TV can be excellent, but its not .. due to the amount of compression applied. Witness SD versus HD digital TV for an example of this....

[Dave]

When the weather turns nasty, digital signals can not be got from the aerial, or satellite dish. Water, snow and wet foliage can act as an R.F. screen. Analogue signals can still get through, albeit with a noisy picture.

Dave

[Paul Martin]

But exactly the same signal was output from the rack that the camera was connected to, as was fed into the TV. The back-room people strived to make sure as little of that signal was lost.

There were problems with cross-colour and the like, but the people producing the programmes knew how to avoid these most of the time.

And still the back-room people strived to make sure that nothing was lost in the transition.

Somewhere about here digital compression got involved and the pictures lost out. It's fine with still pictures, but once you've got movement the clarity disappears.

Even with HD I can see problems with pictures that have movement in them. Ever wondered why demonstration sets have low-movement scenes such as underwater reef filming?

The trend nowadays is to reduce bitrates (even on HD). There's going to be a squeezing of a quart into pint pot come DSO, with the three terrestrial public service multiplexes being reduced to two, with the third to be assigned to HD broadcasts.

If anyone notices a better picture on DVB-T over DVB-S, they must have a duff DVB-S receiver. For example, of the more mainstream channels, More4 is dire on DVB-T.

[Ian Jackson]

I think it is maybe you who are missing the point (or even two points).

Point 1 is that the discussion is about 'Digital Rip-offs', and that (in this specific example) there was no advantage in replacing the old Group A Crystal Palace aerial with a new ('digital'?) aerial. Before and after, the digital signals were OK. After, the analogue signals were worse so, almost certainly, the digital signals were also 'worse' - it's just that you couldn't see that they were.

Point 2 is that a large number of cases (the majority, I believe) majority are like Crystal Palace, ie the digital muxes will be in the same aerial group as the analogues. When this is the case, provided that the existing aerial is in good condition and the analogues are being received OK, there is nothing to be gained by replacing the aerial (and certainly not with a wideband aerial). It's just extra cost. 'If it ain't broke, don't fix it' applies.

[Dave]

No, less so. FM has the advantage in bad weather. It's called the capture effect. In the absence of another FM signal, it is possible to get intelligible info from a weak signal. Albeit, you get a poor picture. With digital, it just packs up below a certain signal level.

Dave

[Bruce]

Oh, I totally agree. I was careful not to mention the FM versus DAB fiasco, for that is what it is.

[Bruce]

Those points have already been made. The thread has moved on - thread drift is hardly uncommon on Usenet, is it.

But thank you for so eloquently setting down what has already been said.

[john]

I'll second that. Have line of site to Emley mast and perfect digi/anal reception. Soon as summer comes, trees in the garden create multipath flutter on Freeview. Things may improve when analogue is switched off and the digi power level increased but the second rate Freeview picture quality will not be improving. TV execs are pushing profits by means of digital overcompression. Flesh tones in particular, are looking more and more like paint-it-by- numbers. :)

[charles]

[Snip]

Indeed so. I'm still using my 'analogue' aerial - installed in 1978.

[Mike Henry]

Did you have both before Easter 2000? The bitrates on DSAT for the BBC in particular used to be far higher, then they dropped them dramatically.

It is fundamentally true for many of the bitrates currently in use, that's the problem. If you were comparing good analogue with the original launch DSAT and DTT bitrates, then yes the digital picture edged ahead.

[Roderick Stewart]

Regardless of anyone's experience, it's a gross oversimplification just to state that either digital or analogue terrestrial television is "better" than the other, because there are a great many factors involved.

Being able to see the whole of the picture, for example, is surely a parameter of quality, and as a decision seems to have been taken only to transmit the whole of the 16:9 picture on digital, analogue is given an unfair disadvantage straight away.

Then there's the deliberate bit-rate reduction which is applied in variable amounts to the various digital channels. When the quality is good it can be very good, but it can also be quite atrocious.

Then there are the effects of transmission and reception, and what happens to the picture when conditions are less than perfect. The two systems behave differently in response to these, and of course everybody's situation will be different too.

And so on. What works well in one set of circumstances may not work in another, but one thing that can be said as objective fact is that digital signals have gone through an extra process that analogue signals haven't.

Rod.

[Woody]

Er, Dave, go read your theory book again. Capture effect has nothing at all to do with the weather although it is a feature of FM.

Capture effect is the ability of a receiver to 'hear' one signal and suppress the effects a co-channel signal, usually on a signal strength basis. It's a long time since I did the theory, but as I remember it, if a tuner had a capture effect ratio of 2dB then it would suppress a signal that was 2dB lower in strength usually by around 30dB - well, in theory at least. If there is no other signal present capture effect does not come into the equation.

And if you don't believe me look at

why does FM come into picture quality since, in the UK, the video signal is AM?

[PeterC]

Same here, probably of similar age.

I'm on Oxford, so wideband.

[Ian Jackson]

Wasn't the rain affecting satellite signals? The analogues are FM.

And does this not depend on whether there's any AGC system? FM receivers often don't rely simply on amplitude limiting. Also, limiting itself is effectively a form of AGC (albeit crude). As the signal gets weaker, the system overall gain winds up so that a constant signal level is presented at the detector, and this brings up the noise level.

As long as the noise is well below the signal, the FM capture effect suppresses the AM noise, and you get a 'clean' signal. However, when the noise becomes nearly as strong as the signal, the recovered signal-to-noise deteriorates rapidly. On FM video, that's when you get the 'sparklies'. Below the 'knee' where the capture effect occurs, the reduction of signal-to-noise is more-or-less inversely proportional to the signal level.

[The Natural Philosopher]

Well I dont find that.

Sports is particularly irritating - you get compression artefacts round all moving objects.

I think, but am not sure, that different sets handle this better or worse.

In my experience, the

ONly have freeview.

It uses more bandwith and carries more information. This shows up.

Depending on how compressed the channel is, and how good the decoders, it can be pretty horrible actually.

[The Natural Philosopher]

Well thats is not the way I have found it. Weak signals are better on digital than on analogue. I have found that if the digital is undisplayable, the analogue is usually a ghost lost noise almost completely.

[The Natural Philosopher]

Its only a feature of wideband FM.

And IIRC the analogue video is AM antyway, not FM.