It's still early days in my Blog, but here I am already, typing up my THIRD post on that wondrous in its Byzantine splendor, steam and string powered world of HDMI cabling.
Truly, if you are looking for things to confound Home Theater owners, and exasperate even skilled installers, HDMI is the gift that keeps on giving! And I say that as someone whose history with digital video long predates even HDMI version 1.0!
Not the least of the problems is recognizing whether something going wrong in your setup might even BE an HDMI failure. And in light of that, I present this humble Field Guide to HDMI Failures.
Let's review what's gone before. In my post on HDMI "Premium Certified" Cables, I pointed out HDMI was intended to be, first and foremost, cheap. (Notwithstanding some companies trying to charge an arm and a leg for it!) It is inherently inexpensive, twisted pair copper cabling, connected at each end to relatively inexpensive electronics. Over the years, the industry powers behind this "standard" have had to learn it just won't work unless they get really REALLY picky about how the cables and electronics are designed. I mean in the early days it was so bad, if you bought a device built with HDMI chips from one chip maker, it likely WOULD NOT WORK when cabled to a device built with HDMI chips from a different chip maker! Over the years, the industry brains working on this problem have progressively tightened the specifications -- sometimes staying just barely ahead of the increased demands being put on these cables, such as the need to support higher video resolutions. The point here being, these evolving specifications are IMPORTANT! Each updated specification, and the associated test procedures and equipment, have enhanced the robustness of HDMI cabling. And the latest such effort is the "HDMI Ultra HD Premium Certified" program -- or "Premium Certified" for short.
Today, for the best odds of a carefree HDMI experience, you should be using only HDMI Premium Certified cabling for ALL of your connections, and if at all possible each of those cables should be 6 feet (2 meters) in length.
Then in my post on Video Turning Shocking Pink or Ghastly Green, I introduced the concept of HDMI Handshakes, and the fundamental role they play in configuring the devices at either end of each HDMI cable to be in agreement on how they will communicate THIS TIME over that cable. I also introduced the industry-mandated copy protection scheme, known as HDCP -- a scheme which is finicky by design (it LIKES to fail!) -- and the concept of HDMI as an "end to end" protocol, meaning HDMI Handshakes involve ALL the devices in the HDMI signal path from the originating source device (which is responsible for driving both the Handshakes themselves and HDCP compliance) all the way through to whatever device(s) are on the far end of the HDMI cabling chain.
I illustrated this with a classic example of how things can go dramatically wrong if the HDMI Handshake fails in its primary job of getting devices in agreement, and pointed out sometimes the most practical solution to a failure like this is simply to force a NEW HDMI Handshake!
Now in a moment we are going to step through that door, and go exploring for wild HDMI Failures, in their natural habitat! So if you need to use the bathroom -- or review those two prior posts -- this is the time to do it. We'll wait.
. . . .
Ready? OK then, here were go!
The Sparklies!
Common wisdom among HDMI users is that HDMI either works or it doesn't work. There's no in between. No, "Well it ALMOST worked, but the image is not quite right!"
That common wisdom is wrong. And the classic counter-example rejoices in the name, "The Sparklies!"
In my post discussing HDMI handshakes, I noted HDMI cables carry both high bandwidth and low bandwidth signals, BOTH of which degrade as they travel the length of the cable. The high bandwidth signals carry the video (and audio embedded inside the video). The low bandwidth signals are used for managing things like the HDMI Handshakes and HDCP copy protection. The "Equalization" circuits in the transmitter and receiver electronics have the job of making sure BOTH types of signal are received correctly notwithstanding that damage.
USUALLY, any HDMI signal failures REALLY ARE an all or nothing affair. You either get no image, or you get a badly distorted image you'd never confuse with being "nearly right". Either the Handshake fails or copy protection mutes the image.
But SOMETIMES you get a damaged image that IS "nearly right". Now this is Digital video we are talking about, so you are not going to see failures you might associate with Analog imagery. We won't see an image that's "out of focus", or with "incorrect flesh tones", or with "raised black levels". All of these things MIGHT go wrong in real viewing but those are not HDMI Failures. They are either problems in how the content was authored or how it was processed by the devices at either end of the HDMI cable.
Nope: HDMI Failures will exhibit faults characteristic of a DIGITAL video stream. And the one you are most like to see is "bit dropouts". Each image is made up of pixels, and each pixel is made up of a set of bits -- 1s and 0s -- defining the color and brightness numbers of that pixel.
Well what happens if a bit goes wrong? If you get a 1 instead of a 0, or vice versa? THAT'S a "bit dropout", and whether you SEE it will depend on how much that incorrect bit actually changes how its pixel lights up.
As detailed in my post on Digital Video, each pixel is represented by three numbers, and those three numbers can be 8, 10 or 12 bits each. One of those bits in each number is the "high order" bit, representing the biggest change in that number. The bit at the other end is the "low order" bit representing the smallest change. If the high order bit is wrong, you are more likely to see the pixel as incorrect than if the low order bit is wrong.
Bit dropouts in the video stream are going to be random, and relatively infrequent. MOST of the bits will be transmitted correctly. Why? Because if the video stream is too messed up HDCP copy protection will have a conniption fit and just mute the video outright.
But if you are having bit dropouts, they will be dispersed over the entire image, and they will be random in nature. That is, different pixels in different locations will go wrong -- briefly -- and then they'll be fine again while some other pixels go wrong. Since the failing pixels are dispersed, you won't see whole patches of the picture go bad. It's just a few pixels here and a few pixels there. The distribution of the failing pixels will also be random. They won't follow any easy to see pattern. And the pixels may shift in either color or in brightness -- varying according to which bit got passed incorrectly THIS time.
All of this means you are going to find it very difficult to spot bit dropouts in natural looking imagery. There's just too much natural variation in the pixels making up the image. Where you are likely to see bit dropouts is in patches of uniform brightness and color. But since, on average, some intermediate bit of a pixel value will be the one that's wrong, the change won't be all that obvious.
Except in one case: When you look at a patch of BLACK!
If you are having bit dropouts, and if you get up close to the screen and focus on a patch of Black, you will see The Sparklies! Instead of being uniform black, random pixels will light up briefly and then go dark again.
If you are watching a "wider than widescreen" movie, you'll have ready-made patches of Black you can check: The Letter Box bars above and below the image. Shield your eyes from the rest of the image and focus on those black bars. Do you see The Sparklies? If so, they are actually happening all through your imagery. It's just they are much easier to spot in those black bars.
Bit dropouts represent excessive degradation of the HDMI high bandwidth signal -- the video itself; degradation beyond what the Equalization circuits in the transmitter and receiver chips can handle. The most likely reason for bit dropouts is simply your HDMI cable is not up to the task of carrying the bandwidth of video you are asking it to carry, at its cable length.
I.e., the fix is to replace the HDMI cable. (With a new, Premium Certified cable!)
The nice thing about The Sparklies is this is not something you need to constantly check. Check every now and again, while playing a high bandwidth video signal -- e.g., 4K/24 or even better 4K/60. If the cable is not up to the task, The Sparklies will be evident. If you don't see them, you can relax -- this is not something you have to check every day or with every movie for example.
It IS something you should check for now and again, because HDMI connections DO go bad. For example you may get corrosion on plugs/sockets, or the plugs may have shifted slightly in the sockets.
New Cable Syndrome
Time and again you will hear people say, I'm having video failures but I KNOW it can't be the cables, because I just replaced them -- and I even got those newfangled, Premium Certified beasties!
These folks MAY be right, of course. They might have an electronics failure, or even a type of video incompatibility between their devices. But if this problem coincides with having just switched to new cables, your first thought should be, "This is a case of New Cable Syndrome!"
HDMI is only friction fit, and the mechanical tolerances are such it's already a bit iffy whether a given plug will work reliably with a given socket. The upshot is, it only takes a small shift of plug in socket to screw things up!
The key report suggesting New Cable Syndrome is that the new cables initially WORKED, but now they are failing. So what's going on?
Well new cables come with two characteristics. First, they've just been removed from their packaging, and second, they've just been installed in place.
The path used for new cables will seldom be identical to the path of the cables they replaced. That may mean, for example, there's more cable weight tugging on the plug in its socket at either end. In addition, new cables still have bends in them -- kinks -- due to how they were folded up for packaging. Those kinks may make it harder to aim the plug directly into the socket, and may tug on the plug once it is in its socket.
The point being, new cables are far more likely to produce shifts of plug in socket, triggering HDMI failures. They will work for a while, but eventually the plug will shift a bit too much, and then they fail.
The cure for New Cable Syndrome is to revisit your HDMI signal path, from end to end, unplugging and replugging each HDMI plug along the way -- both ends of each cable. Make sure the plug is fully re-inserted STRAIGHT into the socket, with nothing -- e.g., cable weight or cable kinks -- tugging on that plug in any direction. If necessary, add some support for the cable near the socket.
A useful test is the "wiggle test". After inserting the plug, grasp the cable about a couple inches back of the plug and give it a gentle "wiggle" while also pressing the cable in towards the socket. In addition to making sure the plug is inserted properly what you are also looking for is whether the cable gives more resistance in one direction as you wiggle it -- indicating there is stress on the cable.
Indeed if you are currently having a failure, the "wiggle test" may help you identify the culprit. See if the image comes back as you move along the HDMI path doing a gentle wiggle behind each plug in turn.
Physical Damage
HDMI plugs and sockets connect via pins which are not immune to physical damage. You may discover, for example that one HDMI socket fails whereas another works without problem for the same connection. Get a flashlight and take a close look at the socket and the plug looking for bent pins. Such mechanical damage is usually beyond your ability to repair. If the plug is damaged the cable should be discarded and replaced. If the socket is damaged, repair will likely require factory service.
It is good practice to be gentle around HDMI plugs and sockets. When removing the plug, and even more so when inserting the plug, focus on keeping the plug oriented straight into the socket. Do NOT force the plug into the socket. If necessary, back off and re align the plug and socket before inserting again.
HDMI cables can also be damaged -- INSIDE their protective sheath. For example if you step heavily on the cable or bend it too sharply around corners it is possible to get a wire break inside the cable, even though the sheath of the cable is not penetrated. Sometimes this will be evident in that the cable works or fails only if it is re-bent in a certain orientation.
A damaged cable needs to be replaced of course. This is not something you can repair.
NOTE: One of the upgrades included in the new, HDMI Premium Certified Cable specifications is tougher criteria regarding the ability of the cable to survive being bent around something -- as commonly happens when dressing cables run from one device to another.
Even with NO Physical Damage, it is possible that a given plug simply won't be a good mechanical fit for a given socket. This is less common today, with the newer, tighter specifications, but if you find a cable works well with one socket but not another, and yet a different cable works just fine with that other socket, then you are likely just seeing the variations in manufacturing tolerances. I.e., if a cable works with a different socket, don't sweat it that another cable fails to work there, even though it works with other sockets.
Or to put it in the more common parlance, "If it works, don't fix it!"
The Video Fails Only When You Power Up Your System!
A very common type of HDMI failure report is things ONLY go bad when you are turning everything On. Any of the possible failure symptoms might show -- but most commonly there is no image at all. Often the problem can be fixed by forcing a new HDMI Handshake -- for example by switching one device to a different HDMI Input and back. Usually the user is tuning things On by using a programmable remote control which is configured to turn on all the devices together.
What's going on here goes back to the concept that HDMI is an "end to end" protocol. The failure is happening because some device early in the HDMI signal chain is trying to do parts of the HDMI Handshake before some later device in the signal chain has woken up enough to respond properly.
Forcing a new HDMI Handshake fixes the failure because now, of course, all the devices have had time to fully power up.
The video is typically muted to black because some device in the HDMI chain has detected an HDCP copy protection failure -- basically because a later device is not responding properly. Indeed you can often tell exactly which device is being grumpy because if you try to bring up any sort of on-screen graphic display -- such as volume or content info -- the display won't appear for that device or any earlier device in the signal chain. However, on-screen displays from LATER devices in the signal chain will appear just fine on top of that Muted video.
The first assumption is the problem must be between that device (no on-screen info displays) and the next device (on-screen info DOES display), but that's often not the case. Why? Again, because HDMI is an end to end protocol. The balky device may be complaining due to a problem in something BEYOND the next device to which it directly connects.
Indeed the most COMMON problem is that the DISPLAY (TV or projector) has been slow to power up.
The fix is to power up your devices in the reverse order of the HDMI signal flow, allowing each of them enough time to power up before you move back to the one just before it. So power up your TV, then wait, then power up your AVR, then wait, then power up your disc player.
If you are using a programmable remote, confirm this power up sequencing works using the separate, regular remotes for each device -- along with getting a feel for the amount of delay you need to provide for each device. Then adjust the configuration in your programmable remote to match.
Bandwidth Related Failures
Another common failure report is that video works fine for some content but fails for other content. A typical report might be, "I can play my Blu-ray movies just fine, but when I try to play my SD-DVD movies the video keeps failing!"
The user is typically convinced this must be a problem in his devices. I.e., his disc player is just not handling SD-DVD discs correctly.
That MIGHT be true of course, but anything that LOOKS LIKE an HDMI Failure -- and video drop outs definitely fall into that category -- almost invariably IS an HDMI Failure.
So the first thing you need to do when faced with a situation like this is figure out what's actually being sent on the HDMI cable.
Suppose this user is using one of the newfangled, UHD (4K) disc players, and happens to have a UHD TV to take advantage of it. Odds are he has the UHD player set to send 4K video to the TV regardless of the content it is playing. That is, the player is upscaling all content to 4K output.
Blu-ray movies are on disc as 1080p/24 video. And that means the player will be sending 4K/24 video to the TV.
But SD-DVD movies are on disc as 480i/60 video. And THAT means the player will be sending 4K/60 video to the TV! Much higher bandwidth! And much more likely to expose problems if the HDMI cabling is not quite up to the task!
The way to sort this out is to force the player to put lower bandwidth video on the cable. For example you might set it to send out 1080p video for both types of disc. The Blu-ray movie will go out as 1080p/24 and the SD-DVD movie will go out as 1080p/60. But 1080p/60 on the HDMI cable is far less bandwidth than the 4K/24 which was already known to work before for the Blu-ray movie.
If this fixes the problem -- if there is now good video for the SD-DVD movie -- you know the player is NOT having problems playing that SD-DVD disc. The PROBLEM is that the HDMI cabling is not capable of handling 4K/60 video reliably.
I.e., it's time to upgrade that cabling -- with new, Premium Certified cables!
The maximum bandwidth signal currently allowed by the HDMI specs is 4K/60 YCbCr 4:4:4 at 8-bits per pixel component (i.e., 24 bits total per pixel). When you install new HDMI cabling in a setup with 4K equipment, it is wise to set some source device to send this video format (temporarily) so you can check whether your new cabling is able to handle this worst case signal well.
Almost all UHD discs and Blu-ray movie discs will not need that. They will send 4K/24 video. But for the few UHD movies that are on disc as 4K/60, and for Blu-ray discs (such as live concert performances) that are on disc as 1080i/60, and for SD-DVD discs, you WILL need the cables to handle 4K/60 video. So it is wise to check up front to make sure they will be up to the task when you need it.
The bottom line is MOST signal failures in Home Theater setups come down to one or another form of HDMI Failure. And far and away the most common REASON for HDMI Failures is the HDMI cabling is not up to the task.
And thus, an excellent Rule of Thumb when signal problems rear their head is Replace The Cables. That's simply the most efficient first step. If that does NOT solve the problem, then you can do more sleuthing. But time and again it has been proven HDMI cables are the most likely point of failure.
And now that you know how to spot HDMI Failures for what they are, you can get right on top of the problem!
--Bob