As HDMI is purely a digital signal I'm intrigued as to how one cable can be better than another? To me it makes sense for speaker cables and other analogue connections, but not for this. Any advice appreciated!

Bevan

Personally, I'm not totally convinced ANY cable makes ANY significant substantial difference. Yes, I have experienced such differences, but not under true double blind conditions and whether my experiences are influenced by bias is difficult to answer.

However, digital cables - if they make a difference at all - will likely have issues at the points of interface (such as cable to connector and connector to connector) and potential data jitter propagation issues at these points. In addition, theoretically as the cable is an electrical conductor, it's possible for impedance mis-matchs across the same points of interference.

Personally, I think that the differences between cables have been hyped beyond recognition. But, that said, HDMI seems to be particularly prone to problems in some instances, and perhaps this goes some way to explain why.

Somehow, I doubt it...

It's a popular misconception that because HDMI is digital then all connections will be the same.

Most people won't have a problem if they're only using a short cable. But if you're trying to send, say, 1080p video over a long distance, as mentioned in the article, then that is where higher quality cables become more important.

Otherwise you wouldn't see different cables rated as compatible for 1080p over 11m, 15m, and so on. There can also be issues with HDCP handshaking and other compatibility problems, but that's a whole other area.

There might be a bit of a 'snake oil' phenomenon with some of the cable-makers' claims (and resulting prices) but you'll find people in the industry who agree that HDMI cable quality matters when dealing with high bandwidth data.

And these people won't just be cable manufacturers with a vested interest but people who make the players and screens, whose interest is simply in customers getting their stuff working effectively.

If you get perfect results with a small cheap or free cable then that's great. But if you have problems, the cable is often the weakest link and the first thing to upgrade. So it's worth gradually starting to pay a bit more in those situations.

CHeers for your comments guys. Still a bit confused though! So, with my set-up (Sky HD box right beneath Toshiba 42WLT66) I'm unlikely to expect a substantial improvement in quality if I were to upgrade the 1.5M HDMI cable that came with my SKY box with a similarly lengthed cable?

The difference between cheapo and expensive HDMI cables isn't likely to be too profound on a 1.5m length. That said, if you try to push too hard - upscaling, trying to split the signal to two sources, stripping the HDCP for some perfidious means - you might find the differences more profound.

It's a digital cable and the 'improvement' is strictly digital. It's not necessarily that a de luxe HDMI cable will improve performance... it's that a de luxe HDMI cable will work in places where a basic cable will not. If you are simply connecting a Sky HD box to a TV 1.5m away, this isn't likely to be a condition where the cable struggles.

But, as Ian rightly points out, if an HDMI signal is problematic, it usually comes down to an underperforming cable.

so given the cable is passing digital signals that must mean the cable is introducing errors - how can that be ?

Well, I was sceptical too and bought a 'cheap' 8m HDMI cable through eBay and it quite simply didn't work properly. It refused to pass the HDCP signal through to the monitor which then refused to show the picture. That cable cost £20. I then spent £100 on a Chord cable - problem solved so there must be something in this.

cdrw651,

In theory, any system that carries a digital signal can introduce errors. For example, data jitter occurs when a signal arrives fractionally behind its anticipated time, causing problems in accurately reading the data in sequence. Transmitter, carrier and receiver can and do all cause jitter problems in digital links.

In this case, however, I suspect the problem is due to foreshortening of the cable's bandwidth due to increased inductance (or possibly se resistance) from using a long run of cable. This is similar to a regular audio speaker cable losing high-frequency information over about 13m. Reduced bandwidth can have a marked influence over data-dependent jitter.

OK, whether the signal to be transmitted is digital or analogue in nature, this is transmitted down a (probably copper) cable using electricity.

In the analogue case the electrical current will be on a sinusoidal nature so continually varying in amplitude. In the digital case, the current flow will simply be on or off.

However, both still could suffer from interference because both just carry electrical signals. Of course, the digital signal is easier to compensate for as there are only two states - on or off.

well I assume the only errors are going to be incorrect reading of a state due to timing errors caused by jitter & delay. Jitter in a passive device such as a cable sounds to be minimal compared to say an amplifier or decoder - I would assume any delays induced due to inductance/capacitance/resistance would be a one of affairs ( i.e. all state changes would be delayed by a constant amount over a period of time) rather than changing rapidly ( I accept they will change with temperature but again unless you have a blow torch on the cable it will be pretty static.

So I'm still not sure I can see much in this. I guess Nyquist, transmission line theory and Fourier transforms might explain some of it but it's a bit late at night for that and I think I've forgotten it all years ago !

Yes, jitter in a passive device is minimal at audio rates - which is why I think the fancy claims made by purveyors of 1m long TOSlink and coaxial digital cables are at best nonsense on stilts - but at the sort of frequencies we are dealing with to parse a video signal, these become more significant, especially when used with comparatively long distance cable runs.

You are on the money when you suggest Nyquist and transmission line theory nails this, though. The problem is signal attenuation and jitter from intersymbol interference. If you look at eye pattern charts of an HDMI signal and compare them to the same signal run through 10m of cable, you'll notice the height of the eye opening will have reduced (due to signal attenuation) as will its width (due to ISI). In the worst cases, the eye of the eye pattern will have disappeared altogether, meaning the signal is swamped.

As you can understand, 'jitter' is a convenient short hand for the above paragraph, which is itself acting as shorthand for a lot of mathematics.

I think this all comes down to...
"Buy a reasonable cable for most domestic purposes" {by reasonable I mean not a £1 knockoff from a cheap shop} and only seek out the more expensive types if you have a problem or peculiar installation.
Whatever cable, the more expensive they get, the less improvement you will see for your cash.
I've seen Optical cables hyped up for having "Gold" connectors; as there is no electrical conductor in these cables having a tarnish free plug does you no good at all! This is typical of some of the rip off claims that some dealers/manufacturers are making to what they must figure are very gullible consumers.

Hello all

HDMI.org (the folk behind the HDMI specs) claim that all 'on spec' HDMI cables up to 5m ought to perform equally well.

Over 5m and the cable can introduce problems - especially so with 1080p.

Lots of folk report good results with relatively inexpensive cables (even up to 15m) - though lots of other folk report problems with these same cables in different systems with the same or different Source and Display devices.

Where your 'installing' a long HDMI cable always ensure you fully test the cable at all required resolutions before you 'install' it into a wall or ceiling cavity.

When you don't want to 'take a chance' there are some long HDMI cables your Supplier can pretty much guarantee will work in all systems at all resolutions.

Joe

will a hdmi cable connect to a sky+ settop box

Yes Lu, that's the easiest and only way you'll get HD TV (up to 1080i)out of your HD box. Just make sure the quality is good if the cable length is longer than 2m or so

This is VERY simple. There is ZERO difference between different types of hdmi cables. If there is a flaw in the signal then there would not be a "loss in colour" but the picture itself will be severley messed up. HDMI does NOT support error correction, so any loss in singal WILL cause the image to simply break up. This is comming from someone with a degree in electrical engineering. Yes when you do long runs such as 10m + then a high quality cable will be needed to ensure the singal makes it there, but again you will know if something is wrong because there will simply be no image. If you do see any difference then this is simply you wanting to see a difference due to speding a ton of money on useless copper.

there is a difference, dont ask me why but there is. me and a friend compared the cable that came with skyhd with a techlink, swapping them around in a kind of blind test. i picked out the techlink every single time, my friend most of the time. the picture definately looks sharper with more depth and colour. also the techlink was twice the length. it was even more noticable running from an upscaling dvd player (denon 3930).

This sounds all very familiar, for years the arguments have been going on in the hi-fi world, even to the point of declaring the use of gold plated mains plugs! I often asked myself 'why stop there' get the electricity companies to dig up the road, replacing that audibly corupting copper with silver threads and even change the sub-station wiring to help get the sound improvements 'I know will result'
Of course cables make a difference, technically its true, I worked in the telecomms business for years and spent hours evaluating cables and interconnects to ensure they met the standards required.
However there are only two tests in the home domestic environment

1. Does it work?
2. Are you happy?

Have just come across this entertaining thread.It immediately brought to mind Ectoplasm, Levitation & out of body experiences,et al.
Thanks to Matthew H for injecting a little realism!.

OK This Should be put on the Home Page of EVERY Trustworthy AV Site (Questioning this one).

http://boardsus.playstation.com/playstation/board/message?board.id=ps3&thread.id=828972&view=by_date_ascending&page=1

Read this, this guy exaplins it perfectly as to why it is physicaly IMPOSSIBLE for the to be any iddference what so ever. If you still belive there to be a difference, then ok more power to you, enjoy your expensive pice of copper but just remember the scientific facts of why that shiny cable is pointless.