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#21 Colin Pykett

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Posted 09 April 2015 - 07:45 AM

In the old analogue TV days a few years ago one could get time of day on-screen (e.g. when viewing teletext) accurate to far better than one second - you could see the seconds counter 'ticking' away.  With the move to digital TV this is no longer possible, which is why time is displayed only to the nearest minute.  The amount of time delay is undefined, and is especially uncertain if there is an internet- type (packet switching) protocol somewhere in the transmission chain because the receiving element (your TV) has to wait until it has assembled a whole screen's worth of info in its memory before it can be displayed.  And there is indeed a difference between the audio and video delays, which is sometimes compensated for but sometimes not.

 

This does not help solve the problem, but merely confirms what others have said.  However it might assist to know that the term for this which most tecchies will understand is 'latency', next time you are dealing with firms such as PC World, Maplin, etc, etc!  (And if they didn't know what it means, they will be dead impressed with your smartness as a customer).

 

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#22 John Robinson

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Posted 09 April 2015 - 09:10 PM

So is it no longer possible to obtain analogue CCTV systems?



#23 dave the pipe

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Posted 10 April 2015 - 10:19 AM

It would seem so. I am hoping now to find something second - hand perhaps.  Presumably if you pay enough you can have anything. I am sure that a director in a TV gallery has instant feedback on monitors from the cameras on the studio floor!



#24 Contrabombarde

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Posted 10 April 2015 - 10:49 AM

This is really interesting - an example of how something that in many respects is an advance in technology (digital over analogue) can come back to bite the unwary.

 

It's a recognised problem in concert halls around the world, so much so that many professional settings and TV broadcasters (Broadway theaters, Sydney Opera House etc al) have analogue video cameras of the conductor feeding to analogue CRT monitors. And a shed full of old CRT tellys round the back as a space for when the monitors break down (I don't even know if anyone still makes new CRTs). Samsung and probably other companies do still make analogue CCTVs for this reason.

 

You can get professional broadcast standard monitors for a price (a few thousands of pounds) which boast typically less than 1 frame per second latency - but at 25 frames per second that still amounts to admitting up to 40ms latency!

 

This is a real problem for avid computer gamers too as they need the picture on the screen to update as soon as they move their joystick. Gamer forums are full of discussions about which monitors have the lowest latency. Interestingly it can sometimes be the cheaper ones (since they have less advanced video processing to articificially "improve" the quality of the image being received from the camera). Some monitors have a "gamer" mode that disables the processing. (Conversely some upmarket audiovisual amplifiers have a built in adjustable sound delay so that you can slow your sound down to synchronise with the delay caused by your expensive TV's built in video processing that slows the picture down - an expensive solution to an expensive problem!) Some gamers advocate connecting a source directly via HDMI as digital out (in your case from a camera with HDMI out) to digital in should mean no additional processing of analogue to digital images (especially if the onboard processer is disabled). Others say use VGA or component out for certain monitors since if they can detect an HDMI signal and assume you want it to have additional processing!

 

If you use off the shelf monitors there are additional considerations. There are two common types of LCD monitor, TN and IPS. TN is cheaper and has a faster response time (which is quite different from latency - it's how long an image persists for on the screen after the source has changed). So TN screens are better for gaming - fast movement can appear blurred. However, they have quite poor viewing angles other than viewed from head-on. If you are sitting at an organ bench and moving your head around, the colours of the screen will shift depending on which angle you are looking at it from. That's not the case with an IPS screen - but it might be slightly more blurry when the conductor is waving their arms around. Ideally you would want an IPS screen with minimal latency and minimal response time - but they come at a hefty price. OLED screens are a third type but are also in the very high price bracket.

 

Frankly your cheapest "best bet" is perhaps to look for secondhand ex-broadcast equipment on Ebay. Failing that if you have the time to try out or seek out off the shelf combinations of camera, cable and monitor that work for you great, or pay for an expensive pro-grade set up. Make sure if you go for professional shopping advice that you explain why you need as close to zero lag/latency as possible. And if the shop assistant doesn't know what lag is, or confuses it with response time, go to another shop.



#25 John Robinson

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Posted 11 April 2015 - 09:28 PM

I posted the question on another specialist site and received the following response:

 

"The recorders are digital. But the inexpensive cameras are still analogue, surely?

The cameras use a digital imaging chip same as CCTV cameras have done for the last 30-odd years. The output is on a BNC, and the signal is basic composite video. Whether there's any inherent delay in the camera's own processing is hard to say if the camera has processing (image enhancement, iris control etc), but with a simple cam I wouldn't expect it to be any different to basic CCTV cams from 20 years ago.

The area with the most significant delay will be the monitor. LCD TVs have inbuilt processing time that delays the picture anything up to 120ms. The answer is to buy a secondhand CRT portable TV. They have no significant delay at all."

 

I hope this may be of some help.



#26 Colin Pykett

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Posted 12 April 2015 - 07:36 AM


The answer is to buy a secondhand CRT portable TV.

 

 

 

I'm afraid there are several misunderstandings in the mind of whomsoever posted that advice, John.  However this is not an AV forum.  But I did get to the LOL stage on reading "buy a secondhand CRT portable TV".  BUY, BUY?  I don't think so.  I had a couple of these in the loft until only the other week and even charity shops wouldn't take them.  So they went to landfill instead, into a special skip which was crammed to the brim with them, all smashed to smithereens of course.  So if you can find any at all, their owner ought to be paying you to take them away I think!

 

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#27 John Robinson

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Posted 12 April 2015 - 09:34 PM

I do take your point, Colin.  We threw out a perfectly good CRT TV a few years ago because no-one wanted it.

Nevertheless, there do seem to be some for sale.  Just one site I found:

 

http://www.ebay.co.uk/bhp/crt-tv






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