By David Meyer, Kordz.
Last month, we looked at why 4K is the next logical step in picture quality, what the difference is between 4K and UHD, and whether there will be any 4K content coming soon.
This month, we will look at the remaining key questions concerning 4K, plus some additional areas of interest:
Will My Current HDMI 1.4 Device Support 4K?
4K was every bit as much a part of the HDMI 1.4 specification as was 3D, Audio Return Channel (ARC) and HDMI Ethernet Channel (HEC). The poor practice of most CE device manufacturers a few years ago to reference their products as 'HDMI 1.4' was done so to declare their support for the then headline features of 3D and ARC. 4K was without exception NOT supported. That is precisely why HDMI Licensing banned the practice of referencing version numbers, as it always was, and still is, uninformative and irrelevant.
There are hardware HDMI bandwidth implications in being able to fundamentally support 4K video. This is covered in greater detail in the 'HDMI Bandwidth for 4K' section further on in this article.
Will Current HDMI Cables Support 4K?
Yes.. well, maybe. 4K as it stands now, requires approximately 9Gb/s aggregate data rate through HDMI. High Speed HDMI cable should be certified to 10.2Gb/s, so theoretically good to go, right? The reality is that HDMI has actually been cruising to date, as we have generally been using only 4.5Gb/s out of the 10.2Gb/s available. With 4K, we will finally start to really use the capacity of High Speed HDMI, so you had better make sure that the cables you choose really are what they say they are.
Many claiming to be High Speed actually are not. There are two reasons for this:
1. When the new Standard and High Speed labelling was introduced in 2010, it was accompanied by advice that you need Standard HDMI for 720p/1080i, and High Speed for 1080p. That led to a misconception that 1080p and High Speed were the same thing. At 4.455Gb/s and 10.2Gb/s respectively, clearly they are now. Many cables claimed to be High Speed simply because they worked at 1080p. HDMI compliance at 4K is a whole other story.
2. High Speed simply sounds a whole lot sexier than Standard. If you were in marketing, which would you use? Some reputable brands did not succumb to such practices, but many did.
The bottom line when it comes to choosing cables is stick with a vendor that you know and trust, and who can assure you that 4K will be supported. You do NOT need a new version cable for 4K support. Nothing has physically changed in the HDMI cable specification since 2003, other than the optional addition of the HDMI Ethernet Channel, which has nothing to do with 4K. It all comes down to the bandwidth supported by the individual products. Do not assume that you need a new cable, and for the purposes of giving interoperability its best fighting chance, always try to stick with native HDMI cabling.
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Stick with a vendor who can assure you that 4K will be supported by your cable.[/caption]
What's Happening with HDMI 2.0?
There has been a lot of chatter about HDMI 2.0 for some time now. The good news is that it is real, it is happening and it is not too far away. It is too early to reveal specifics, but here are a few facts.
Further to the six main questions above having been addressed in Part 1 last month and Part 2 this month, there are some other elements to 4K that are worth exploring. In no particular order, these are as follows:
HDMI Bandwidth for 4K
If you take nothing else away from this article, remember this: 297MHz HDMI Clock, or 8.91Gb/s data rate. They are the minimum numbers you need for 4K support in devices and cables alike. To appreciate what this really means, it may help to compare these numbers to what HDMI-enabled devices have been using to date.
The very first ever HDMI-enabled devices back in 2004 contained HDMI chipsets - transmitters, repeaters or receivers - that could support 165MHz, or 4.95Gb/s. This was surprisingly enough for 1080p right out of the gate (1080p60 is 4.455Gb/s). This means that all devices, ever since the release of HDMI, have fundamentally had the chipset capacity to support 1080p. Not as much has changed as you may think! The rest came down to the resolution, firmware and features etc, of individual products.
With the 2006 release of the HDMI 1.3 specification, Deep Colour was the headline feature, spawning a new generation of HDMI chipsets that increased the HDMI Clock to 225MHz, and the data rate to 6.75Gb/s aggregate. This unlocked the ability to go to uncompressed with 12-bit Deep Colour. To this day, most devices on the market are still employing 225MHz HDMI silicon.
4K up to 30fps requires 297MHz, or 8.91Gb/s. If current devices are using 225MHz HDMI chipsets, clearly that is not enough. New hardware is required, as the bottleneck is literally in the silicon. Firmware updates alone will not cut it.
4K TVs will all have at least one HDMI input using the new generation 300MHz HDMI chipsets, as introduced by some leading semiconductor manufacturers from last year. Also, this is just one of the new additions to Sony's PS4, amongst many other things. In time, 300MHz will be ubiquitous, just as 225MHz was from 2007 onwards.
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4K TVs will all have at least one HDMI input using the new generation 300MHz HDMI chipsets.[/caption]
However even 300MHz can only support up to 4K at 30fps. To get the more ideal 60fps (also encompassing 4K 3D), the next step is likely to be 600MHz, or 18Gb/s. That is 180 times faster than the best theoretical connection proposed by the multi-billion dollar NBN ((Australian) National Broadband Network), and HDMI needs to deliver it in real time. Those are serious numbers.
Colour Depth
It is worth noting that HDMI already supports 10- and 12-bit colour without any bandwidth premium with YCbCr 4:2:2 (Blu-ray) and 4:2:0 (DVD) formats. But if we are talking uncompressed (RGB or 4:4:4), then 10-bit comes with a 25% premium, and 12-bit with a 50% premium over standard colour. That's okay when we have supplied headroom in the HDMI chipsets, as we do currently with 225MHz for 1080p.
With 4K there is no room to move. We need 297MHz as a minimum, but the chipsets are just a nudge above that at 300MHz. That means 4K30 will only be offered in 8-bit uncompressed colour, but 10- and 12-bit will still be available for compressed YCbCr formats. That's all in theory based on current standards - we'll wait and see what the Blu-ray Disc Association do with the BD specification.
Frame Rate
Frame rate is every bit as important as resolution when talking about bandwidth. It is however, often the neglected appendage, the geek speak that hangs off the end of what the marketers like to really focus on. As an example of how important frame rate is, consider that 720p60 actually has more active pixels per second than 1080p24. Frame rate matters.
First-generation 4K will be limited to 30fps - half that of what we commonly use for 1080p(60). 4K is four times the resolution of 1080p, but being only half the frame rate is why it can fit into double the bandwidth, not four times. HDMI 2.0 will bring to the table 60fps, so at that point, bandwidth really will quadruple over 1080p60. Hang on!
Conclusion
HDMI is the ubiquitous standard for digital HD connectivity. For it to deliver 4K video system-wide, all HDMI chipsets in the signal path must support at least 297MHz Clock, or 8.91Gb/s data rate. Look for anything above these numbers in the product tech specs. HDMI cables should be demonstrably High Speed. In fact with 4K we will actually start to use High Speed HDMI for the first time ever, really challenging HDMI connectivity finally. 'With Ethernet' is irrelevant.
A few years from now, we will look back and wonder what all the fuss was about over the lack of content. It really is not a hindrance, rather a necessary step to delivering full-system 4K video performance.
It's coming. It's real. It's awesome. Be ready!
David Meyer is the Founder and Managing Director of Kordz, specialist in reliable long-reach HDMI. Following the launch of HDMI 2.0 at IFA in Berlin in September 2013, Kordz became the first approved HDMI 2.0 Adopter in the world, outside of the HDMI Forum.
www.kordz.com
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