Evaluation of Results and Final Conclusions

I wanted a bird's eye view of the cable tests to see how the lengths affected overall performance. I wanted trends and general principles. Here's what the tests looked like charted out:

As you can see by the chart here, the drop-offs mostly occur (in bulk) at theoretical limits and that last stage. For the most part, not a lot of cables have difficulties passing real-world current bandwidth requirements of today's 1080p sets. For cables under 3 meters the results are almost flat.

Subjective Results Back Home

I wasn't content to simply check off a box and condemn massive amounts of cables to criticism unless they actually failed when brought back to a real-world environment and tested. What I found surprised me - and brought the entire thesis of this article into question. First of all, it's important to note that most projector and display manufacturers are adding cable EQ circuits into their systems. This is a way to counteract the filter effects of a longer cable and help the system to correctly read the digital data. In addition, HDMI 1.3 removed the restrictions on overshoot which prevented the use of pre-emphasis on source components. Now, sources can improve performance at higher speeds and when using longer cables. As it turns out, most manufacturers are doing exactly this.

We took two of the worst performing cables of the bunch, a RAM Electronics 50' HDMI cable ($130) and an equally challenged Tributaries (Series 9) 15 meter cable ($899). Both understandably fail eye pattern tests at even 720p resolutions. Both, unfortunately, also claim HDMI 1.3 support at up to 10.2 Gbps bandwidth and with Deep Color support. It was fairly obvious that both of these cables would fail real-world tests when connected to a 1080p source.

Except that they didn't.

I saw clean video on two separate displays. I even used two different sources - one HDMI 1.3 and the other sporting an older HDMI 1.2 chipset. Then I got real desperate and nabbed an old HDMI 1.0 source (A Helios NeuNeo player) and slapped it up to triple check the signal.

What?!? Scratching my head I searched in vain for a way to get them to fail. I couldn't. Not at 1080p or any other resolution. Finally I actually resorted to connecting the two huge cables end-to-end. That netted me sparkles at 720p/1080i and absolutely no picture at 1080p with our HDMI 1.0 player. OK, so there are some limits after all. That's good to know.

What I expected to see on failed cables was something like this, or worse:

What I got was this - but only after connecting two very long cables end to end:

When I finally got a result, sparkles abounded on the screen, even shooting horizontal lines across parts of the picture in frequent intervals. But this was only after traversing over 65 feet of HDMI cable. So far, my theory on longer-run HDMI cables was a near-bust. Sending 1080p content through this 25 meter juggernaut from an HDMI 1.3-capable player (the Playstation 3) yielded this:

What was occurring was real-time video, but with frequent, rapid-fire areas of snow on the picture which made the movie pretty much unwatchable. Periodically, the entire picture would turn to snow or flicker off for a moment before it came back and attempted to render itself to the best of the double cable's potential. This was significant as it demonstrated to me the importance of pre-emphasis which is available via HDMI 1.3 sources and not present on older HDMI 1.0 devices (remember, with the HDMI 1.0 source we got nothing on the screen at all at 1080p).

The real test, I thought, would be to send 12-bit video through the system to the display. That would ramp up my video from 1.485 Gbps to around 2.23 Gbps. That simply wasn't in the cards, however. Despite all the hype about Deep Color - you can't get it. Not anywhere. It might as well not exist.

Statement on Deep Color 12-bit Signals

We interviewed Jeff Soo H. Park from HDMI Licensing, LLC about the lack of 12-bit ("Deep Color") sources on the market. Here was his response:

There are number of sources that support 12-bit color output (PS3, Blu-ray players) but no 12-bit content exists at this time [emphasis mine]. That doesn't mean you will not see any benefit from these 12-bit devices. Many of these 12-bit sources may have features that "upconvert" current 8-bit content to 12-bit, depending on the manufacturer. This concept is similar to how some HDTVs upconvert 60Hz source video into 120Hz video.

Like any new technologies, we will see the components (TVs usually first) start to build-in the new features and, when there is enough momentum, the content producers follow with content. We saw this with 1080p, for example. A similar trend will be likely occur for 12-bit.

With no way to cram 12-bit data into the line, I was stuck testing cables at 1.485 Gbps rates. That's practically child's play for most applications and I wasn't terribly surprised to find that even the "worst" cables passed video in real world tests. Heck, I even passed 1080p over a DVIGear 30 meter passive HDMI cable. 30 meters!!! And this coming from a company who won't sell a 10 meter cable without a cable EQ (included in the price of the cable) because it is concerned with quality.

It turns out that manufacturers aren't idiots; and I bet more than a few realize that they can spec their cables higher due to the lack of content to prove them wrong. In short, they are getting away with it... for now.

What About Future Formats?

Normally we'd say "who cares?" but with the history of HDMI, and the fact that people are putting HDMI cables behind their walls, this is a very valid question to ask. Are you really willing to put a cable in the wall that doesn't have the ability to handle any potential future bandwidth increases HDMI Licensing decides to throw into the electronics industry? To give us a fighting chance to check cables against future formats, we actually added two more empirical tests. First, we maxed out the HDMI 1.3 spec, setting up a test for 3.4 Git/s. Next we stuck on the equivalent of 1080p at 8-bit, but at double to frequency, or 120Hz. This equates to 4.98 Gbit/s. Right now only displays are performing 24/60Hz to 120Hz conversion, so this isn't necessarily anything we'll see anytime soon (hopefully never if you ask me) but it makes for an interesting scenario. As you may or may not know, the Sony PlayStation 3, being essentially a souped-up PC and graphics card, can already (theoretically) do 120Hz output over HDMI, provided this feature is activated via firmware (it's not currently).

When we added these advanced "future" formats, our eyes were opened to the real danger of using "just any old HDMI cable." They don't all work, or at least they don't look like they'll work according to our tests. Even at less than 5 meters. For example, while Gefen's 2 meter cable we tested works flawlessly with the full capabilities of HDMI 1.3, it doesn't pass our Max test at 4.98 Gbit/s (the only 2 meter cable that didn't). At 15 feet, Infinite Cables failed to pass the maximum HDMI 1.3 spec (3.4 Gbit/s). Other companies' 5 meter cables, from Blue Jeans, Cobalt Cable DVIGear, MonoPrice, RAM Electronics, WireWorld, and Next Generation Home Products (3 meters on this last one) passed the current 1.3 spec, but showed that they may not be ready for future formats at this length - failing the 4.98 Gbit/s data rate test.

Will Active Cable Solutions Save the Day?

We were unable to test active cables with the HDMI cable testing system. If we had, the insurance company for Monster Cable would have had words with us since it would have essentially fried the hundreds of thousands of dollars worth of components we were using to measure the cables. The system documented above cannot be used on active cables without special add-ons that weren't available to us. Any cables with embedded or active electronics would have had catastrophic results.

What we were able to do was test some active solutions on our failed 65+ foot run above. For example, remember that unavailable 1080p image when using the Helios player? It came back and looked just fine when we inserted an active HDMI Cable Extender from DVIGear. It also eliminated the stuttering, snowy signal from the PS3, bringing it right back to pristine picture quality. Active HDMI solutions, whether internal or external to the cable are going to be a big deal as the technology expands. What it told me is that not all is (necessarily) lost when your cable can't cut the mustard - provided you are using decent cables to begin with. I don't think any cable EQ in the world is going to help a truly bad cable, but for those who buried HDMI in a wall back in the days of 720p - there's still hope.

Conclusion

Well, what started out as a quest to prove the fact that longer HDMI cables really matter ended up schooling me in the fact that real world performance differs very much from lab results. It also demonstrated that not all manufacturers' cables are created equal - nor will all of the cables labeled as "HDMI 1.3-ready" likely pass all of the potential aspects of category 2 (3.4 Gbps) cables without help.

I have to come away saying that most cables under 4-5 meters will pass just about anything in today's arsenal of 1080p - and that's likely to include Deep Color if and when it ever makes an appearance (not likely soon due to current Blu-ray limitations). For cables over 5 meters it's a good bet that you'll want to stick with trusted manufacturers who deliver on their specs. For long cables, Blue Jeans Cable, DVIGear, MonoPrice, Monster Cable 800HD, and WireWorld seem to be the best bets of the cables we tested - however the price variance between these cables is revealing. We're sure there are also other cables we didn't test which are also likely to perform well. Some of the other manufacturers, such as NGHP, RAM Electronics, Sewell Direct, and Tributaries also showed themselves to be great performers at <7.5 meters, however they either didn't have longer length cables or they didn't supply them in ~10 meter lengths for our testing.

Your take-away from all this should be the following:

• At lengths less than 4 meters you can just about use silly string (OK, not really) and get HDMI to pass at any current resolution. At less than 3 meters you'll even extend that to 12-bit color and possibly the next crazy idea HDMI Licensing decides to throw at consumers. Don't spend a lot on these cables and if you want to save money you won't let anyone at a big box store talk you into buying from them.
• At long lengths (over 10 meters) you really need to pay attention to the manufacturer if you don't want to risk running into potential problems with 1080p and future formats such as Deep Color. With that said, just about any cable at or under 10 meters will pass 720p/1080i and nearly everyone will pass 1080p at 8-bit color as well.
• If you have an existing HDMI cable and are running into problems, we'd suggest at least attempting the insertion of an active component at the sink (display) side. This is going to be far cheaper than ripping out your walls and re-running new cables - and likely just as effective.
• HDMI has proven to be a moving target and there is no telling what crazy (likely unnecessary) format they will try to push down the cable next. Due to this, it's always good to "overbuild" your cable install, especially if it's a longer distance and going to end up behind drywall.
• If you're not prone to upgraditis and think 1080p will be your maximum resolution for the life of your install, don't sweat it...

There are going to be exceptions to all these "rules" but in the end I'd have to say that I really thought I'd see more differences in the real-world performances of longer-length cables. Since we're all basically pinned at 8-bit 1080p, I didn't. It's likely you won't either. So all those people saying "buy any cable you want, it doesn't matter" are, for the most part, correct - at least until manufacturers advance to 12-bit software and signal transmission. Where they are not accurate is in assuming HDMI (since it is digital) is either "on" or "off" (it either works or doesn’t). HDMI signals can be partially corrupted as you saw above. The other area in which they are off concerns the future. If and when 12-bit "Deep Color" video truly comes to market (as more than just a listed spec) individual cable situations can (and likely will) change. For this reason take all of the above measurements and principles into account and make sure you build your installation wisely.