Why you should never pay more than $10 for an HDMI cable (Infographic)

Have you ever gone into a Best Buy or similar and seen the cable selection? The "cheap" cables are $50, and the Monster cables are sold right beside them. Many people compare prices on the TV before coming into the store, but are not armed with good information when the salesperson tells them that their $1200 TV is worthless without $250 in cables.

That's still not correct.

For HDMI in particular, there's no error correction at all on the video data (though there is on the audio and control data).

So if one bit gets flipped in the video data as it goes through the cable, you're going to see that wrong bit on screen. You'd have to have an insanely high bit error rate for your eyes to notice it, but it's there, and it gradually gets worse as the error rate increases.

What could flip a bit in a cable? Any number of things. EM interference from outside a badly shielded cable. EM crosstalk between conductors inside a badly designed cable. Signal reflections at badly designed connectors. Basically anything that can happen to any other cable, whether the signal that goes over it is considered to be analog or digital.

I assume the reason HDMI applies EC to the audio and control data is that errors in those channels are more noticeable to the user, whereas errors at reasonable rates in the video will mostly sneak by.

The HDMI spec at http://www.hdmi.org/download/HDMI_Spec_1.3_GM1.pdf is a great source of information about this.

The real time to worry about the quality of those cables is when you go over 6 feet.

Clearly you've never had an Ethernet Cable that got caught in a door. Or was terminated poorly. Or doesn't have the insulator sheath under the crimp. Or run parallel to a set of Florescent light ballasts. All of these events can reduce performance on Ethernet without causing it to fail outright.

There is a reason why every single TIA/EIA 568 cable plant is carefully tested for things like Near End Cross Talk (NEXT), Latency, Skew, etc..

There is also a reason why there is an entire _discipline_ dedicated to ensuring that the "Digital" signal not only has a channel, but a meticulously crafted one. (See: http://www.linktionary.com/t/tia_cabling.html for details)

To reiterates the OP - there is no "Digital Signal" - signals are analog in nature, and they need an analog channel to transmit them. That analog channel needs to be engineered carefully to get the lowest EBR (Error Bit Rate) possible.

What's interesting is the Failure case of the Digital CODEC on the other end - some may reduce transmit rate in the presence of an increased EBR resulting from dropped packets. Or some may seize up and cease to function. In the degraded case, having a pristine analog channel from the transmitter to the receiver will certainly result in a better digital signal.

There is also the issue of future proofing - We're installing an entire plant of Category 6a cable right now in one of our data centers for a gigabit environment - Category 6a is like the "Monster" version of Category 5e/6 - It seems like a douchey way to do a network install, except when you consider the following - (1) this cable plant will be in use for 10-15 years, (2) We're testing a bunch of Nexus 5010s that will likely make good use of that 6a for 10 Gigabit. So, in addition to passing _today's_ signal flawlessly, it will also pass tomorrow's. This might be an important factor if your HDMI cable is being run through hard to access cabinets/walls.

Now, with all that said, it is still probably the case that the $150 Monster Cables (under normal circumstances) don't have a lower EBR than a $10 cable, but, in the face of RF interference, It may actually be a better performer. I don't know, but I wouldn't discard the possibility without a bit of research and education.

I guess the argument should have been that once you cross a certain threshold, cable quality doesn’t matter. That was of course also true for analog signals (human senses are only so good), but the transition from good signal to bad signal might have different characteristics with digital signals.

While a image from a analog signal will only get noisier and noisier as signal quality decreases, images from a digital signal will first show artifacts and then just stop displaying altogether. That’s a rather sudden transition. One second the signal is there, the other it's gone. Something like that just doesn’t happen with analog signals. (I’m basing this on my experience with terrestrial digital broadcasting – could be totally wrong for HDMI connection but I doubt it.)

I would guess that how sudden that transition is has something to do with the error correction and the codec of the signal. How many wrong bits can the error correction reconstruct? And, as soon as the wrong bits get past the error correction, how many wrong bits can the decoder handle and still reconstruct a image (albeit one with artifacts)? It would certainly be interesting to know how that problem was solved for HDMI connections. If you know the maximum bit error rates for your cables figuring out which are the right ones should be easy, given enough testing :)