By C. I. Source
Although HDMI 2.0 has been out for a while, this technology still
has a dark shroud of mystery surrounding it. Dealers and manufactures are afraid of HDMI while
customer demand is looming. We’ll examine some of the issues we’ve had to deal
with as we get underway with this new frontier in Part 1. Be sure to watch for
Part 2, Into the Future of HDMI in
our next installment.
The question is: “As an industry,
how do we salve the fears and provide the client with what they need to move forward with the new HDMI interface?”
To fully understand the new technology, let’s review. Let’s
look at how we evolved, where we are presently, and where we are headed in the
future:
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n the beginning, there was DVI created by silicon image
which was intended to be a computer video interface that provided a true
Digital High Speed Video connection over a relatively short distance. DVI
performed as intended -- but not without problems creating a roadblock to
future implementation. Some of the
issues were the lack of a single Plug/Wire standard; the inability for the
signal path to travel more than 15’ consistently; no audio standard; and a very
large terminal.
Not long after DVI was introduced, the movie and TV
industries started looking for ways to secure their new “HD” content. They felt motivated by and ultimately
compelled to limit market availability due to what they assumed were their
intellectual property rights. They would not release “HD” content to without a strict
level of “Intellectual Property” protection. To fix this shortcoming, Silicon Image
(creator of DVI) took the functioning structure of DVI and the HDCP protection
scheme developed by Intel and put it all together into a smallish terminal that
carried the High Speed Video, Multi-Channel Audio, Intelligence and Security
together as one.
The original HDMI Spec 1.0, 1.1 and 1.2 (2002-2006) allowed
for 5 Gbps of data transfer, this supported 1080P, 8 Bit color, Multi-channel
Audio and EDID/HDCP. In 2006 the HDMI
1.3 spec was released, this covered several new features and an expanded
bandwidth of 10.2 Gbps. This revision
had the first actual cable performance change (from 5 to 10 Gbps) since the
introduction of HDMI and is where we still are almost 10 years later! The HDMI
1.4 spec introduced in 2009 added features to the electronics but did not have
any cable changes except for the “not yet used” Ethernet support.
This brings us to HDMI 2.0 and the new 18 Gbps standard.
When HDMI 2.0 was introduced with much Fanfare in September of 2013 (wow time
flies!) there was a lot of misunderstanding and misinformation. This new
version of HDMI made a giant leap in bandwidth and now calls for 18 Gbps
bandwidth capability.
Whoa….wait a minute, did not HDMI LLC say that they would
not need to institute a new cable spec to support this? Yes, HDMI stated, numerous
times, that the current 1.4 “high end” cable spec will do everything that is
needed for this new format.
And that brings us to the reason for this article: How is
this going to work? More importantly, how do we plan for the future?
Here (in HDMI LLC’s
opinion) is how it is supposed to work:
Equalization! HDMI assumes that if you have a “true” High
Speed cable that is in fact capable of 10.2 Gbps and if you can throw 25 db of
EQ onto the signal at the display side you will be able to recover enough data
to get a “true” UHD 4K picture.
There are of course some serious issues involved with this
plan. A vast number of cables are not really 10.2 capable, even though they are
rated high speed. That means a fail. The display side equalization, while
over-all adaptive, does not appear to be frequency
specific adaptive. This means that if your cable does not have a very linear
signal loss between 10 Gbps and 18 Gbps (with a max loss of 25 db) you will have
a statistically high opportunity of failure. This theory also does not work
well with longer distances and extenders, of any sort.
Here (IMO) is how it
is working:
How is it that
there are systems with long cables and extenders working with UHD right now?
Well, they really aren’t doing HDMI 2.0.
HDMI 2.0, more importantly UHD, only needs about 9 Gbps to
carry all of the current formats. I call this HDMI 2.0 Lite.
Aren’t UHD and HDMI 2.0 the same thing? No, no they are not.
Thinking of the HDMI 2.0 spec as the USA, for example, UHD is about the size of
Rhode Island! So while all UHD formats fit into the HDMI 2.0 Spec, and as a
general rule the HDMI 1.4 spec, there is no way that all of the HDMI 2.0
features fit inside the boundaries of UHD.
Here is how current UHD 4K/60 works inside of the HDMI 1.4
spec:
Current UHD started showing up in products such as the Sony
4K server in the summer of 2013. This version was only 4K/30 meaning the
picture was refreshed 30 frames per second (FPS.) While this looked great on
static or slow moving pans, when there was an action scene the video became
very jittery. This did not go over well with the consumer. The push was on to
get the video refresh rate up to 60 FPS. The only way to accomplish this with
the cables and digital roadways that are available is to cut corners on the “chroma sub-sampling rate.”
This Chroma sub-sampling rate is represented as three numbers, 4:4:4, 4:2:2 and 4:2:0.
This is very important to both the overall quality of the picture and the
bandwidth needed to carry the signal. 4:2:0, available in UHD, cuts down on the
necessary bandwidth by doing a lot of data averaging. This is done so they can
cram a lot of data, in theory, into a small pipe. In 4:4:4 each and every pixel can display any
color independent of any other pixel. In the 4:2:0 pixels are arranged in
groups of 4 which all show the same color. This is how they cut down on
bandwidth, instead of needing enough bandwidth to provide every pixel its own
color information, they now only need enough to cover a quarter of that need.
Thank You to AVS Forum for this Graphic
That’s enough for this issue, don’t you agree? Stay tuned
for Part 2: The Future of HDMI in our
next issue.
Be sure to send me your questions and any feedback you may
have. I’d love to hear from you!
