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HDMI Quality

Discussion in 'Cables & Switches' started by bobbypunk, Jan 27, 2004.

  1. bobbypunk

    bobbypunk
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    I am not sure on the technology behind HDMI so would hope someone can answer this question.
    Is it possible to make a better quality HDMI lead?
    I would like both answers:
    and is it possible that it could be made better (Even by an unnoticable amount)?
    If so, Is it practical? (Worth the results or cost compared)
     
  2. ailean

    ailean
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    I believe the spec of HDMI kit is reasonably detailed about signal strengths and this includes the licensed cable makers. So to carry the logo the cable must pass tests no matter what the length. This should in theory mean the cable will work and the kit at either end should operate within the same tolerances. ;)

    Of course once the prime time cable makers get there HDMI gear up and running we should see plenty of expensive versions appearing, but they all have to pass the same tests so I'd guess the practical differances will be a lot less then most other cable types which have no spec to comply with.

    Just my guess thou. :)
     
  3. Nic Rhodes

    Nic Rhodes
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    yes in theory it will be possible just like DVI but in practice, with the compatibility testing, differences should be relatively small. Even mass market cables should have good performance. The days of cable madness are finishing.....
     
  4. rscott4563

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    I was thinking the same thing myself but then I read this from the HDMI website:

    $700 for a HDMI cable which should be no better than a $50 molex one!!

    Seems just like cable madness to me! :zonked:

    Cheers

    Ryan
     
  5. _Sin

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    It does seem to me like insanity kicks in when people are dealing with digital cables.

    For electrical ones I'm sure a better quality cable would be more reliable over a distance, but for the kind of lengths involved for most hifi cabling, frankly a piece of wet string ought to offer no difference at all to the most finely crafted piece of hand-woven purest silver.

    The signal may look nicer on an oscilliscope but the zeros and ones will still be zeros and ones, unless it's very broken indeed.

    I only give some thought to the build quality for the sake of the cable not falling apart if I accidentally drop something on it.

    My favourite all-time hifi techno-babble was the comparison review I saw in a certain hifi magazine between two optical cables, and discussing the finer points of the sound produced by both.
     
  6. bobbypunk

    bobbypunk
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    From what was just said, HDMI themselves are admiting that there is a possibility of improving the quality. In theory if not practice.
     
  7. Nic Rhodes

    Nic Rhodes
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    It is not to do with 0s and 1s :(
     
  8. bobbypunk

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    no, red green and blue would be more accurate, but also it has to carry the exact colour information.
     
  9. _Sin

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    I've yet to hear anyone actually try and explain why a digital signal is improved by a more expensive cable...
     
  10. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Mr Sin,

    You can read TAG McLARENs white paper on their cables at their web site.

    The Beekeeper has also written posts on this site explaining about digital signal transmissions and the cables required to do it properly. It's not about more expense it's about using the correct cable.

    Gordon
     
  11. _Sin

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    I think I've read the paper you're referring to...

    I take the point that you can't just transmit data at any rate you like down any old bit of wire of arbitrary length. Distortion of the signal will in various ways accumulate until the signal is disrupted. However I take issue with assertions that there will be any kind of subtle difference involved.

    In the majority of cases digital signals do not degrade gracefully - they either work, or they do not. Any subtle change in the signal being transmitted should *not* affect the digital data.

    If I have a digital signal I want to get from A to B I expect the precise same data coming out as went in. If anything happens to it on the way that isn't deliberate processing, it's broken.

    In the case of an audio interconnect the bandwidth required is pretty small. A video signal contains a lot more information, so I expect to have to have a certain quality of cable. But having gotten a cable which *works*, buying a more expensive one should have precisely zero improvement.

    A recent project I was involved with involved capturing data at significantly higher rate than is required by consumer video applications*. Transmitting this data over a short distance using a bunch of barely-shielded ribbon cables to the logic analyser did not result in any of the data being lost. If we looked at the captured analog waveform there might be some irregularities there, but they were not enough to influence the digital signal.


    *actually if you wanted to transmit a 2880x1800 frame at 100fps and at 48bit colour you'd be in the same ball-park.
     
  12. bobbypunk

    bobbypunk
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    but surely the subtleties of audio and images are alot more complicated than raw data. Physics laws say that there will always be loss (No matter how insignificant). With Digital transfer without conversion there must still be a limiting factor stopping the exact image being displayed (as it must degrade).
    Surely the material used, the amount of interference and how well the actual connections are made must make a difference.
    I'm not disagreeing straight out but it's just the "precisley zero" comment that goes against everything i've been taught:
    Any movement or conversion will always cause a loss.
     
  13. _Sin

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    The important distinction is between the signal, and the information encoded within it. With analog, the signal *is* the information (or at least it's in fairly direct corelation), and any degradation to the signal will affect the information content. With digital, it's a bit more complex.

    Digital signals start with a bunch of 0's and 1's in the source bit of hardware. These are converted into some kind of electrical (or optical) signal. When the signal gets to wherever it is going it is quantised back into 0's and 1's. So really it's already subject to massive signal-loss at reception anyway - you throw away the vast amount of detail in the signal and just look at whether it's more on than off. Provided any signal degradation isn't serious enough to make it confuse the two states then the actual information will be completely accurate.

    Audio and video in the digital domain *are* just raw data, the same as anything else.

    Of course you can get as sophisticated as you like when deciding what to do with that data, and how to convert it to something physical (like sound and light) - but the cable that moves the bits from one place to another really doesn't need to do more than just work.

    So you *do* lose some of the signal (as you say, thats pretty much inevitable) - it's just that the information is encoded in such a massively redundant and robust form, that it takes a relatively large amount of damage before the signal loss translates into information loss.

    The conversion *to* digital will involve loss. The conversion *from* digital involves a certain amount of high-tech guesswork.
    But in the digital domain, there's really not much excuse for data not getting from one place to another completely intact. And once you have that licked, you can't really improve on it...
     
  14. bobbypunk

    bobbypunk
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    So it's not necescerily going to be a case of better quality cables but more a case of the decoding and encoding could be improved. So you're final choice would be in the quality of the product you buy. Is this right?
     
  15. _Sin

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    Yes, thats pretty much what I'm saying. So long as the cable is good enough then all my money would be invested in getting the best possible bits of hardware on either end of it.

    For example, mpeg decoding (i.e. DVD playback) is massively open to interpretation by the hardware. CD playback slightly less so, but can certainly be affected.

    I bought a cheap(ish) DVD player for my parents for Christmas, and although they love it to bits I can see the difference in output (to my ageing but good reference player) from a mile away.
     
  16. Nic Rhodes

    Nic Rhodes
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    I sort of agree with what you are saying but……I think we need to put some context around it

    We are not talking about getting the 0s and 1s through successfully, it is all the other bit that cause the problems particualrly with digital. Some systems are more ‘resistive’ to these (DD / DTS) than others (PCM). They all get the 0s and 1s. In fact you have to do something really bad to stop the 0s and 1s.

    HDMI works somewhat differently to flawed interfaces like SPDIF as people have learned loads over the years. In fact it seems a really decent solution that is easy to use. I for one endorse it.

    Any cable needs to be ‘fit for purpose’. This really isn’t that difficult or expensive to do correctly but each cable needs to be ‘taylored’ for what it is doing. I have posted loads on this. The HDMI cables are basically doing this pretty well anyway and therefore a standard £8 is all you might need. I am sure there will be those who ‘want’ to spend £800 on an HDMI cable, well let the fools, I would rather educate people on what needs to done.

    A cable will never ‘improve’ a signal, at best it will transport the signal with the minimum number of degredations. This applies to any cable. At the moment with analogue and digital cables, a huge amount of money is spent on cables (when it doesn’t need to) and not enough on the equipment but I large put this down to lack of education on what is needed. I try to change this.

    There is a huge amount of ‘miss information’. I think the thing that sums it up best for me is no one is willing to do proper blind cable A / B testing despite the offer of rewards posted on this site by an eminent journalist. I have found NO ONE who can tell the difference between two ‘properly designed engineered cables’. I think that say volumes. They can’t tell a difference because there isn’t one!

    Green vs yellow anyone ;)
     
  17. _Sin

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    Yup, I think we're in agreement here :)

    Of course if anyone still has 800 to spend on a fancy digital cable, I have this nice bridge that might interest you...
     
  18. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    I think that Sin and Bee, although both agreeing that a well engineered cable is best, do not actually fully agree on the other point.

    Not wanting to put words in Bee's mouth but he is of the opinion that cables do sound different when transmitting digital information like PCM. It's just that properly engineered cables do not. In this respect using a wet bit of string may well get all the data transfered but there would still be a difference in sound between the string and the properly engineered solution.

    Gordon
     
  19. _Sin

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    I'd be interested to hear anyones opinion on why that might be the case. The only things I can think of off-hand would be timing issues with an unclocked signal (but I can't see the cable having much bearing on that) or a more subtle issue of the digital cable creating an EMF which doesn't affect the digital processing, but has a catalytic effect on the analog part of the system...
     

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