[Badvok]

Originally Posted by SgtWilko

If I was a broadcast engineer who needs >30m cable runs, I'm sure I'd have a more appropriate, higher specification cable/system, than HDMI to move A/V about.

Yes, professionals don't use HDMI, they use various forms of SDI.
I accept your points about why the industry adopted HDMI rather than devise a new standard or latch onto the work already being done on DisplayPort, and just like the VHS/Betamax result, I regret that this has happened but it's not something anyone can really change. I for one will always buy equipment that supports DisplayPort in preference to stuff that is HDMI only, wherever possible.
The key thing that I was trying to get across to people on this thread is that just because it is digital, HDMI is not a simple works/doesn't work interface.
Serial data transmitted over a single balanced twisted pair is very reliable as shown by Ethernet standards but all those standards also impose higher levels of error checking above the physical link layer that HDMI doesn't. HDMI also requires four twisted pairs that all need to be balanced with each other to retain synchronisation over even short distances.
I do get your point that since it is streamed video it doesn't really matter that much if there are some errors, that there is no point trying to re-transmit, and that most people will not notice. Personally, I like to know if I'm getting the best picture possible.
Although you don't need to spend much to get a fully working HDMI cable, very cheap cables are, IMO, unlikely to have very good balancing of the pairs or good robust crimp/solder joints, but this is purely my subjective opinion (which some other people here think I'm not allowed to share without hard evidence).

[Nigel Goodwin]

Originally Posted by Badvok

The key thing that I was trying to get across to people on this thread is that just because it is digital, HDMI is not a simple works/doesn't work interface.

I suggest you try reading the previous posts, both yours and others

Your frequently expressed opinion was that a cheap lead in some way gives a slightly inferior picture, this is complete nonsense. While I agree that a FAULTY lead will give problems that a working lead won't, the fact that it's digital will make the fault fairly catastrophic, and not 'slightly inferior'. The most common HDMI lead faults are not working at all, but other faults are flashing and 'sparklies' just as you would expect with digital failure - nothing 'subtle', and never a 'slightly inferior' picture.

Any HDMI lead, that isn't faulty, will give EXACTLY the same picture quality as any other - you might care not to believe it, but the rest of the world does.

Although you don't need to spend much to get a fully working HDMI cable, very cheap cables are, IMO, unlikely to have very good balancing of the pairs or good robust crimp/solder joints, but this is purely my subjective opinion (which some other people here think I'm not allowed to share without hard evidence).

You're allowed to put it forward as your OPINION - but you keep putting it forward as a FACT - and it's only YOUR opinion, with not the slightest shred of evidence to support it. All evidence, and everyone else in the world, disagrees with your personal belief.

You keep posting quotes from the spec, but these have nothing at all to do with it - we all know there's no error correction, and we also all know (except you obviously) that there's no need for any.

[Badvok]

Originally Posted by Nigel Goodwin

The most common HDMI lead faults are not working at all, but other faults are flashing and 'sparklies' just as you would expect with digital failure - nothing 'subtle', and never a 'slightly inferior' picture.

In YOUR OPINION, my opinion differs based on personal experience.

WRT the other drivel you've posted, please grow up and stop putting words in my mouth to bolster your weird agenda (whatever that is).

[Muzer]

Just bought a couple of 1m Signalex-brand HDMI cables from Poundland. They have the actual HDMI logo embossed into each connector, which would definitely imply they're genuine and certified. Now if I can only figure out how to get the packet open without searching for scissors



I have an idea for a good experiment - get a good full HD LCD TV (LCD because plasmas seem to have natural "noise" that would disrupt this experiment). Turn off any frame interpolation options for simplicity's sake. Call up a static screen (eg the splash screen on a Blu-ray player) and stare at it closely for a few minutes. See if you can see *any* pixels change colour for a frame. If they do, then you're obviously right. If not, then obviously that cable is fine (if it wasn't, they would surely show in such a test). I don't know how accurate such an experiment should be, but I would expect it would be quite easy to spot errors, even if the magic "error-smoothing" interpolation that there is no evidence for happens.

[Badvok]

Originally Posted by Muzer

Turn off any frame interpolation options for simplicity's sake.

I'm not sure this is possible on most TVs. The closest mine has is a 'Game Mode' which might reduce the image processing but I doubt it eliminates it totally. Especially since the colour space at least needs to be adjusted for the particular LCD filters used.

Originally Posted by Muzer

Call up a static screen (eg the splash screen on a Blu-ray player)

Not a good source because the large areas of solid colour and/or smooth gradients would make any compensation done for errors incredibly simple and hence unnoticeable.
As I've repeatedly said, I don't think you can know for certain if there is a marginal fault in the cable or if interference is having a small effect - that's the problem with HDMI (in my opinion).

[Nigel Goodwin]

Originally Posted by Badvok

In YOUR OPINION, my opinion differs based on personal experience.

You had a single faulty lead (according to your previous posts) - how did you come to the conclusion that cheap leads give poorer pictures?, when that wasn't even your experience with the one faulty lead?.

WRT the other drivel you've posted, please grow up and stop putting words in my mouth to bolster your weird agenda (whatever that is).

The only one here with an agenda appears to be you?, telling people to spend more than they need to on an HDMI lead - and it's you spouting the drivel trying to justify it.

[Badvok]

Originally Posted by Nigel Goodwin

You had a single faulty lead (according to your previous posts) - how did you come to the conclusion that cheap leads give poorer pictures?, when that wasn't even your experience with the one faulty lead?.

Please stop trying to put words in my mouth - I have never said anything of the sort!

Originally Posted by Nigel Goodwin

The only one here with an agenda appears to be you?, telling people to spend more than they need to on an HDMI lead - and it's you spouting the drivel trying to justify it.

So your agenda becomes clear, you are simply an arrogant fool who likes to misrepresent other peoples comments to wind them up!

[Nigel Goodwin]

Originally Posted by Badvok

Please stop trying to put words in my mouth - I have never said anything of the sort!

As I said before, perhaps you should try reading your own posts?.

Oh quite true but what most people don't realise is that, unlike DTT, HDMI has no obvious 'digital cliff' the data can be mangled very slightly or quite a lot and you might never notice unless you run a side-by-side comparison.

From your post #52, where you imply that poorer pictures are possible (which they aren't).

So your agenda becomes clear, you are simply an arrogant fool who likes to misrepresent other peoples comments to wind them up!

Not at all, merely someone who can't stand by and watch incorrect advise being posted.

[alan_m]

Originally Posted by Badvok

In YOUR OPINION, my opinion differs based on personal experience.

Having recent first hand experience designing for these kinds of interfaces, my opinion is that even with the slightest mismatch in timing or with missing bits the faults on the resulting picture cannot be missed.

[Badvok]

Originally Posted by Nigel Goodwin

As I said before, perhaps you should try reading your own posts?

Or even, get this, it is a truly amazing concept, YOU should try reading them!

[Badvok]

Originally Posted by alan_m

Having recent first hand experience designing for these kinds of interfaces, my opinion is that even with the slightest mismatch in timing or with missing bits the faults on the resulting picture cannot be missed.

As I've said before, I think how noticeable the errors are will depend on the display processors. I'm pretty certain there are very few displays that actually display the data exactly as it comes out of the HDMI lead.
My own experience, though limited, showed that the errors weren't obvious until they got bad enough that they impacted on the HSYNC symbols.

[Muzer]

Considering that HSYNC/VSYNC data presumably wouldn't be sent down the same leads as the picture (but I haven't read the spec so correct me if I'm wrong with this), surely it could just be the case that the data lines went faulty on your cable, meaning that the picture was perfect before it started happening and those missing lines afterwards?

[SgtWilko]

Originally Posted by alan_m

How many households are currently receiving video over IP on many kilometres of poor grade twisted pair originally designed for frequencies of less than 5KHz? i.e. the legacy telephone system.

Sorry, I might be being thick, but I'm not sure what your point is here...

SgtWilko.

[spiney2]

professional video links use sdi over coax. hdmi was only ever intended to link consumer base unit or tv receiver to screen over a very short distance.

as previously estsblished there is some implied error detection since rll coding is used. the official spec says its up to individual manufacturers how this fact is used by various different devices.

[alan_m]

Originally Posted by Badvok

The key thing that I was trying to get across to people on this thread is that just because it is digital, HDMI is not a simple works/doesn't work interface.

In this context, yes it is. Over a short distance (a couple of metres or more) a poor quality cable is likely to work exactly the same as a good quality cable.

Over longer distances the poorer quality cable will show deficiencies BUT when the signal fails to arrive correctly the viewer will not fail to see the results.

Serial data transmitted over a single balanced twisted pair is very reliable as shown by Ethernet standards but all those standards also impose higher levels of error checking above the physical link layer that HDMI doesn't.

Not necessarily - where I work multiple videos are sent reliably over Gigabit Ethernet. There is error detection but mechanisms for re-transmitting packets are not used, There is no point in a real time system. The technology is being used on a small local network, with,say, a dozen nodes..

HDMI also requires four twisted pairs that all need to be balanced with each other to retain synchronisation over even short distances.

Although the cables may be sold cheaply in your local pound shop the machines that are twisting the pairs and assembling multiple pairs into cables cost £100,000s. Why wouldn't the wires in the cables be matched? soldering/crimping to the connector is an unknown but the wire lengths would have to be mismatched by a good few inches, which is maybe a bit difficult to do in a such a small connector.

I do get your point that since it is streamed video it doesn't really matter that much if there are some errors, that there is no point trying to re-transmit, and that most people will not notice. Personally, I like to know if I'm getting the best picture possible.

Over compression of the transmitted signal by the broadcasters means that you are not getting the best picture possible But that's life, some people just want more dross channels rather than fewer channels with a better technical quality.

Although you don't need to spend much to get a fully working HDMI cable, very cheap cables are, IMO, unlikely to have very good balancing of the pairs or good robust crimp/solder joints, but this is purely my subjective opinion (which some other people here think I'm not allowed to share without hard evidence).

There will always be a market for the Russ Andrews cables

Do the £5/£10/£20/£50/£80 cables from the high street retailers have good balanced pairs, good/robust crimp terminals etc. I for one would not be able to tell from the packaging or just looking at the made up cable that it has well balanced pairs or the crimps are well made.

Albeit not HDMI cables, but I have taken apart the shells on many connectors and have often found the £2 cable is a lot better made than the £10+ cable.

Unfortunately, the saying "you get what you pay for" doesn't necessarily hold true when it comes to buying digital connection cables as some retailers use them as a cash cow to fleece a technically uneducated public.

Knowing that a £1 cable can work in an identical way to one costing £100s over the distances that most people arrange their boxes and TVs doesn't stop someone buying a more expensive cable that may have smaller shells or may be mechanically more robust. However, as you have indicated, these shouldn't cost much more than the pound shop offerings.



You can usually tell if a cable is ~@*! because they will have gold plated the connector

[munstru]

Comet tried to flog me HDMI for about £40 when I bought the TV about 5 years ago ..... told them to get lost and bought TV somewhere else for taking the *i$$

Originally Posted by Night Watchman

And if you want the views of an expert see this article from TechRadar entitled "Why you don't need to spend more than £2 on an HDMI cable" !

http://www.techradar.com/news/video/...-cable-1071343

[SgtWilko]

I think I may have confused people. My reference to professional video links was due to the statements towards the beginning of the article that Badvok linked to:

Originally Posted by Badvok

On issues with HDMI: http://www.audioholics.com/education...tter-with-hdmi

For those that haven't read the article, but have read my comments, in the article they stated:

Had the DVI standard been designed by broadcast engineers rather than computer engineers, things probably would have turned out very differently.

Consider, by contrast, what the broadcast world did when it needed to route digital video from point to point. The result was HD-SDI, high-definition serial digital interface. One coaxial cable can route an HD SDI signal hundreds of feet without errors, with no repeater hardware or EQs in the line. Had the consumer industry opted for a coaxial-based standard, we'd be able to do the same in our homes.

Hence my reference to professionals, as the article seemed to be suggesting that professional broadcast engineers would have developed a better standard, and better by the articles definition seemed to be something that can run for professional length cable runs. I wasn't trying to state that professionals should, or do use HDMI for > 30m runs (or at all), just that you should use the right tool for the right job.


Sorry for any confusion,

SgtWilko

[Badvok]

Interesting quote from that TechRadar article:

"Should I buy cheap HDMI cables on eBay?

We found HDMI cables selling on eBay for as little as £1.29, but they can't be as good as bone fide big brand cables, can they? Well, actually … for short-runs – i.e. taking video from a Sky box to a TV nearby – the chances are that these kind of cables are absolutely fine.
They come from exactly the same no-name factories as the expensive cables, but haven't been through pricey testing procedures, so they could be duds – and they're low price suggests they've probably without decent shielding – but these logo-less HDMI cables are from the same production line as cables that have passed the test.
Buying from eBay is in some ways risky, but at this kind of money, who cares? If it doesn't work, throw it away! We would, however, give cheap, long HDMI cables the swerve."

As I've said all along, don't spend ridiculous amounts, but if you go super-cheap you are taking your chances. Though I also don't believe it is always a simple matter to determine when it is not working.

[spiney2]

part of the dvi/hdmi idea is to avoid coax. the trend being towards current loops that have some but limited energy loss. since in coax the loss is dielectric absorbtion. following the trend of baseT etc ...... one reason is the amount of copper used .......

[AndrewLG]

This thread will be coming out in a paperback version soon!

Or a condensed version titled:

For normal use don't spend a lot of money for an HDMI cable unless you want to make someone else rich (and yourself poor)!

The content is the same as the title.

[spiney2]

use of current loops does resist external interference.

use of coax wd have required some sort of framing system and data separation. whereas each of the 3 hdmi video ccts is synchronous with master clock.

its only intended to work the short distance between receiver and screen. which it does..