Best Practice: What is 4K Exactly?

At a recent show I attended, I was rather taken aback with the thousand-mile stares that came back to me when I asked manufacturers about the 4K video formats that their equipment supported.

‘It supports 4K’, they replied. Not helpful… 

As we enter a world where 4K HDR content will be the norm, we are now up against the limits of copper cabling to reliably transmit high bandwidth AV signals at distances greater than around 5m.

It’s all about bandwidth
HDMI 2.0 has increased the potential bandwidth from 10.2Gbs (Giga bits per second.) on HDMI 1.4, to 18Gbs. That’s 18 billion binary bits per second. This is an important step to being able to deliver higher quality content than we currently have. The following chart (courtesy of Kordz) illustrates the required bandwidths of various video standards.

Aylett_There is no such thing as just 4K. The bandwidth needs to be qualified

There is no such thing as just 4K. The bandwidth needs to be qualified.

You can see from the chart that simply saying ‘4K’ is not particularly useful as there are many different video formats within the ‘4K’ tag. The bandwidth of a video signal is made up of:

1. Number of pixels on the screen. 4K (3840 x 2160) is around 8 million pixels, whereas HD (1920 x1080) is only around 2 million pixels.
2. Frame rate. Blu-ray is 24 frames per second. Content is available up to 60 FPS, and even higher if in 3D.
3. Colour Depth. How much information is needed to encode the colour and brightness of each pixel. HDR10 (The SMPTE standard for High Dynamic Range) will need 10bits, with the current Dolby Vision and upcoming REC2020 colour standards both needing 12 bits.
4. Chroma Sub Sampling. This is a way of compressing the signal by reducing the amount of colour information per pixel. 4:2:0 chroma subsampling is visible compression. 4:4:4 is uncompressed.

We can see from the above table that 4K, 60 FPS, 12 Bit Colour, 4:2:2 needs almost the full 18Gbs bandwidth of HDMI 2.0. A Kaleidescape Strato and most UHD Blu-ray players are able to deliver this — though they can be configured for lower quality, but still 4K, depending on the available transmission bandwidth.

The vast majority of current long distance HDMI transmission technologies are not capable of carrying greater than 10.2Gbs. This will ultimately limit the quality of signal that you are able to send to a display device in the future. Hardware can be upgraded, installed infrastructure is very difficult to upgrade in a finished building.

Planning for the future
For the systems that you are designing now, consider doing the following:
1. For sales staff, please take the time to understand what ‘4K’ means so that when discussing the options with customers you can explain the above in non-technical terms in order to justify your design recommendations and the extra costs associated with them.
2. Consider specifying fibre on the majority of your projects. This will be the only reliable way in the future that 18Gbs can be delivered reliably over distance. Today (July 2016) there are some companies who are on the cusp of releasing fibre products for the above application. These will be in two forms:

A. Pre made ‘HDMI’ cables that are in fact fibre cables with active electronics in the plugs. This cable will be powered using the 5V Hot Plug Detect pin on HDMI cables and will be distance limited (Length TBC but probably around 50m) due to limited available power.

B. Active boxes that plug into either end of terminated 50/125 OM4 fibre. The fibre can be installed, terminated, tested and then left dark for future use if needs be. These systems will carry HDMI at up to 18 Gbs, Gigabit Ethernet, IR, RS 232 and ARC (Audio Return Channel). An added advantage to this system is that you will be able to use simple and inexpensive HDMI matrix switches instead of HDBaseT systems. Please note that currently there is no commercially viable silicon to make an 18Gbs HDMI Matrix Switch. These will, however, be available by the end of the year.

Aylett_High bandwidth source components have separate outputs for audio and videoHigh bandwidth source components have separate outputs for audio and video.

3. To connect 18Gbs capable source devices, use both of the HDMI outputs:

A. The Video output is full 18Gbs bandwidth HDMI 2.0a and HDCP 2.2 and goes directly to the display device. If this is taken via an AV processor it is highly unlikely that the processor will support pass through for 18Gbs HDMI 2.0a and HDCP 2.2.

B. The Audio output (HDMI 1.4) goes to the AV processor and just carries audio and no video.

There will be a cost implication to implement a fibre infrastructure. This can be more than justified by the hugely increased flexibility that this infrastructure can bring for both current and future high bandwidth AV distribution. A simple single Cat-6/6A cable is highly unlikely to ever be able to reliably carry 18Gbs over distance.

Fibre is not scary any more
Once upon a time, terminating fibre on site was the preserve of a highly trained technician with an extremely expensive machine. Now, companies like Cleerline make fibre systems that are just as quick, easy and inexpensive to field terminate as an RJ45 plug. This removes the previously most expensive part of fibre installation, which was the labour costs involved in termination.

Aylett_Fibre is now easily terminateable on site using simple tools and connectors

Fibre is now easily terminateable on site using simple tools and connectors.

As consumer electronics become more and more commoditised, as an industry we must always strive to offer the highest performance levels possible. This means that we have to dig deeper than simple consumer labels such as ‘4K’ to truly understand how to deliver the best possible experience. This now means that we need to question our suppliers to clarify exactly what they mean by ‘4K’. Ask them what bandwidth their products support. If this is only 10.2Gbs, you are potentially restricting the level of A/V quality you will be able to deliver in the future.

Plan for this future by specifying and installing fibre. Though nothing is ‘future proof’, fibre is set to become the new high bandwidth transmission medium of choice.

Peter Aylett is a world-renowned speaker and lecturer in residential technology, and the Technical Director at Archimedia, a multinational high-end residential integrator in The Middle East. He is also currently Chair of CEDIA’s International Technology Council Applied Content Action Team, and a regular contributor to HiddenWires. 

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