HDMI connections for Blu Ray - Misleading information in What HiFi ?

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Gerrardasnails

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Sep 6, 2007
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Andrew Everard:jam_man:Id be very interested to see someone who reviews these cables and sees such massive differences to be able to award one star or 5 stars and see how they did over a blind test, say putting 2 5 star leads in a test of 100 1 star cables and see if they can pick them out by sight.
My guess is no one would manage to...

We actually did a blind testing session with some forum members as part of a recent The Big Question article. They saw (and heard) differences, as you can read here.

And you still get people questioning the proof - like GazzyP! I've sat on the sofa and I can hand on heart say that nothing is staged and if anything Ket and the team were quite interested if we noticed something that they were not expecting.
 

GazzyP

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Jul 3, 2008
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So if I get a better quality USB cable for my printer - will I get clearer print outs?

If the copper cable between my modem and the telephone exchange are better quality will my websites be clearer?

Isnt this the whole point of a digital signal??

Did anyone see on the Gadget Show a year or so a go they did a side by side comparison of a 5 quid cable and a 100 quid cable. They could not tell the difference.
 

The_Lhc

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GazzyP:Did anyone see on the Gadget Show a year or so a go they did a side by side comparison of a 5 quid cable and a 100 quid cable. They could not tell the difference.

Regardless of whether or not HDMI cables make any difference, invoking the Gadget Show is not exactly going to do your argument too many favours...

They thought low bit-rate mp3 sounded better than CD if I'm not much mistaken.
 

Andrew Everard

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May 30, 2007
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GazzyP:So if I get a better quality USB cable for my printer - will I get clearer print outs?

If the copper cable between my modem and the telephone exchange are better quality will my websites be clearer?

Isnt this the whole point of a digital signal??

If you read back through some of the many threads on this subect, you'll see that such arguments have been cited many times before, and there are fundamental differences between the kinds of data you mention and real-time audio and video transmission.
 
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Anonymous

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The code that makes up an audio/video stream is very complex; some people seem to think that the picture will just either be on or off.

The various parts of the picture such as colour info, luminosity, timing etc each have masses of digital info which constitute their data. It is quite possible for some data to be corrupted yet a reasonably accurate overall image to be formed. Data error correction is very much a part of a digital design.

I have noticed that my sky HD signal can be weak enough to cause some artefacting to varying degrees such that the picture is still recognisable but there are some coloured streams like trails of digital blocking. My picture does not entirely freeze just because some data is clearly incorrect.

It is possible therefore for some cables to pass on more of data more accurately. After all compressed mp3 files still form a passable facsimile of the file they were created from and yet data is 'missing' by design.
 

professorhat

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Dec 28, 2007
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chudleighpaul:IMHO if someone pays £100 for a cable then they couldn't bring themselves to admit that they cannot detect any difference in picture quality.

I bought a mains cable for £130 and sent it back for a refund as I didn't think the improvements warranted the extra cash. Hence why I'd implore others to do the same - always buy from somewhere with a money back guarantee. I'm glad to see the OP did actually experiment with it - at least his judgement not to buy a more expensive cable is now based on experience as opposed to theory.

And I would also point out, no one in this thread or at What HiFi would recommend attaching a £100 HDMI cable to a budget TV and BD / DVD setup - clearly the money can be better spent elsewhere. Common sense needs to play a part and the 10% rule (i.e. spend about 10% of your system's worth on the cables to connect it all together) is still the most sensible one I know.
 
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Anonymous

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One thing to understand is that DVI/HDMI was brought in with the ability to provide copyright protection which was difficult to achieve in component video. Thus the implementation of HDMI was not firmly based with the consumer in mind, component video can be used to provide high definition video, HD is not exclusive to a digital signal. It could be argued that the HDMI std did not pay too much attention to the problems of sending a high frequency signal along twisted pair cables, ie copyright protection was more important.

It is correct that a digital signal is a stream of 1s and 0s and it is also true that if you transmit a digital signal and the same stream of 1s and 0s is decoded at the receiver then you have no loss, in effect a lossless transmission. But a 1 and zero is actually represented by a voltage level and obviously these levels need to change and this change takes time, it cannot occur instantaneously. In a perfect word these voltage states of 1 and 0 would be represented by a perfect square wave, but for a variety of reasons the wave is never perfect square (harmonics, infinite bandwidth required and noise considerations).

This change in state is handled by circuits which have capacitance and impedance and when you add in a cable you also change the capacitance and impedance of the circuit. Adding capacitance and impedance to the circuit has the effect of delaying the time it takes to change state, (t=1/CR). Further, impedance mismatches and crosstalk between the twisted pairs adds random noise to the signal.

What this means is that our square wave at the transmitter looks a loss less square when it is received, if you viewed this on an oscilloscope you would see a definite difference in the shape of the transmitted to the original. Now this can be handled at the receiving circuit as long as the signal can be sampled and reconstructed to the original. This sampling in HDMI is at a very high frequency at has to occur at a certain instant on the wave, ie if the sample occurs on a part of the wave that has not reached a certain threshold then you have will have errors in the signal.

In simple terms if you kept making the cable longer you would end up with a signal that was just noise and contained no data, therefore the quality of the cable has to play a role in the transmission of the original signal. Now I don't have experience of HDMI but I do have 20 years of experience of transmitting signals from ROVs (vehicles on the seabed) and these include some fairly high frequency signals. What I can tell you from that experience is that there are a lot of factors that dictate the noise on a signal and the quality of the cable plays a huge role.

In this thread it has been mentioned that cheap cables have been tested against more expensive. One thing to bear in mind is just because it is more expensive does not necessarily make it better, it comes down to the spec, but one thing that is certain is that a cable that is better designed and built will have less noise at the end of it. Also when testing cables the data being transmitted is vital, a close up scene with little motion and little change in colour will not test a cable as much as a scene with lots of colour changes and lots of fast motion. Further it is not just down to the cable, the size of the display, how good the source and display decoders/encoders are also plays a big part, if these are not great in the 1st place then a high quality cable cannot wave a magic wand.

Buying an expensive cable does not necessarily guarantee you will get a better picture than a cable a quarter of the price, as stated there are many factors that influence the quality. But would I spend a lot of money on equipment and then buy cheap cables, not a chance, just like if I owned a Ferrari I would not put on cheap tyres.
 

carter

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Aug 27, 2008
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ive just replased my budget hdmi lead with a piece of string and could see no loss in picture quality
 
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