Ultra High Definition televisions, online video services, 4K UHD Blu-ray players, next-generation video game consoles, multi-channel home theatre amplifiers, home theatre speaker packs and many other audio-video devices are now well established in our living rooms. Sophisticated and high-performance, they allow us to live particularly immersive audio-video experiences. However, the use of these devices can sometimes be confusing, especially when it comes to their HDMI interconnection.
The promise of HDMI connection
The move to all-digital end-to-end with the adoption of HDMI connectivity is expected to simplify connections between different products and improve picture and sound quality.
At first glance, the connection simplification is there: a single interface makes it easy to connect a UHD Blu-ray player, a DTT/SAT decoder, a UHD-4K TV set and a home cinema amplifier, carrying both UHD 4K picture and HD sound.
But with use, the promise of improved picture quality is unfortunately not always kept. Why is that? Firstly, because the unbridled rush to high definition and 4K has literally drowned out users with an abundance of HDMI cables, some of which are clearly not performing well enough to exploit the full potential of Ultra High Definition 4K. Second, because the multiplication of standards for HDMI link and HD and UHD content is plunging some users into an abyss of perplexity when it comes to choosing the right HDMI cable for their needs. While the fourfold increase in the number of pixels compared to HD 1080p is the most common way to define UHD 2160p resolution, other features such as a wider dynamic range (the famous HDR technology) and a wider colour space (Deep Color sampling and colour depth with Deep Color technology and BT.2020 colour space) are also important.
These features impact the quality of the perceived image much more visibly than resolution alone (the quality of the pixels displayed counts as much, if not more, than their quantity). While they obviously require a video player and a compatible UHD 4K TV or UHD 4K projector to operate properly, they also require an HDMI cable capable of carrying a large amount of data per second without loss.
Several questions arise for home cinema enthusiasts who have invested in high-performance UHD 4K equipment and wish to acquire HDMI cables capable of carrying all digital audio and video signals in the best possible conditions:
- What to choose among all the HDMI cables on the market?
- How can you be sure that an HDMI cable is compatible with Ultra High Definition (UHD 4K) at full speed and supports HDR, HLG and Dolby Vision standards as well as videos with an extended color space?
- Vendors often recommend HDMI cables from well-known but very expensive brands. Is it really necessary to spend that kind of money to get good performance in HD 1080p and UHD 4K?
- How to find your way between HDMI controller standards (HDMI 1.3, HDMI 1.4, HDMI 2.0, HDMI 2.1…) and HDMI cable certifications (Standard, High Speed, Premium High Speed, DPL 10.2G, DPL 18G)?
To find your way through the plethora of HDMI cables on offer and find out which one is best suited for which use, you can refer to two certifications: the one set up by the HDMI Forum, and the one from the independent laboratories DPL Labs.
But before examining these certifications in detail, it may be useful to review some of the characteristics of the UHD 4K image resolution and their implications for HDMI linking.
Why would I prefer HDMI cables certified for UHD 4K?
What does UHD 4K resolution imply?
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| As the resolution increases, so does the level of detail and image size, requiring an HDMI cable that accepts a higher data rate. |
It’s easy to understand that a 2160p resolution image requires more bandwidth than a 1080p resolution image, since it consists of four times as many pixels. But the resolution is not the only term in the equation. Frame rate (24, 50, 100 frames/second), colour depth (the more or less precise gradation scale) and colour sampling are also important factors, also requiring a large bandwidth. Each of the different possible combinations of resolution, frame rate, colour depth and colour sampling then requires a specific minimum bandwidth. The higher the image specifications, the greater the bandwidth required.
The transmission of UHD 4K images from a source (UHD Blu-ray player, Internet box, etc.) to a UHD 4K TV is therefore primarily a matter of bandwidth. Not all cables are the same and many are not designed to provide sufficient bandwidth. The result is a dull and distorted picture, unrelated to the possibilities offered by UHD, or no picture at all in the worst case!
Colour depth and dynamic range
In addition to offering four times the resolution of 1080p HD images, UHD 4K UHD images have a wide dynamic range (HDR – High Dynamic Range) and a specific colour space (Gamut BT.2020 or Rec.2020). With a 10-bit colour depth encoded on 10 bits, i.e. 1024 possible brightness values for each colour component of each pixel (for memory, a pixel is composed of 3 sub-pixels: a red, a green and a blue), it is 1.07 billion colours that can be displayed on the screen. The BT.2020 gamut thus covers 75% of the spectrum visible to the human eye, whereas the Rec.709 (or BT-709) colour space, which defines the HDTV standard, covers only 35% (16.7 million displayable colours).
Even more than the gain in resolution, the extension of the dynamic range and colour depth really makes a difference in terms of image quality. Because the colour gradation is more progressive, many more intermediate shades between different colours can be obtained on the screen, without the phenomenon of posterisation, which causes bands of different shades to appear instead of a true gradation. On the other hand, the additional information to be transmitted between the UHD 4K source and the UHD 4K TV or UHD 4K projector requires more bandwidth.
HDMI Forum certifications
The HDMI Forum is the official body behind the HDMI standard. Hundreds of brands of audio-video equipment manufacturers adhere to it and comply with its standards, which guarantees the interoperability of the different devices connected to each other in HDMI, whatever their brand.
In addition to defining the HDMI standard, the HDMI Forum offers a certification program for HDMI cables based on their performance and their ability to carry different types of audio and video streams (mainly according to the data rate they allow):
Standard HDMI cable
Compatible with the 720p and 1080i resolutions used for the transmission of TV programmes via DTT, cable and satellite.
Standard HDMI cable with Ethernet
- Compatible with the 720p and 1080i resolutions used for the transmission of TV programmes via DTT, cable and satellite,
- Presence of a specific channel dedicated to data transfer via a network. This functionality is only operational if the two connected devices integrate this possibility.
HDMI High Speed Cable
- Compatible with HD 1080p and UHD 4K (24/25/30 fps) resolutions,
- Support for 3D video,
- Deep Color compatible.
HDMI High Speed With Ethernet Cable
- Compatible with HD 1080p and UHD 4K (24/25/30 fps) resolutions.
- Supports 3D video,
- Deep Color compatible,
- Presence of a specific channel dedicated to data transfer via a network. This functionality is only operational if the two connected devices integrate this possibility.
Premium High Speed HDMI Cable
- Compatible with HD 1080p and UHD 4K resolutions including full frame rate (60 fps – 60 fps),
- Compatible with different HDR standards (HDR 10, HLG, HDR Dolby Vision),
- Compatible with wide color spaces such as BT.2020,
- Compatible with color sampling up to 4:4:4.
Premium High Speed HDMI Cable with Ethernet
- Compatible with HD 1080p and UHD 4K resolutions including full frame rate (60 fps – 60 fps),
- Compatible with different HDR standards (HDR 10, HLG, HDR Dolby Vision),
- Compatible with wide color spaces such as BT.2020,
- Compatible with color sampling up to 4:4:4,
- Presence of a specific channel dedicated to data transfer via a network. This feature is only operational if both connected devices integrate this po
ssibility.
Ultra High Speed HDMI Cable (HDMI 2.1)
- Compatible with UHD 8K60 (60 fps – 60 fps) and 4K120 (120 fps – 120 fps) uncompressed with HDR, as well as 10K120 compressed, with certified bandwidth at 48 Gbps,
- Compatible with different HDR standards (HDR10/HDR10+, HLG, HDR Dolby Vision),
- Compatible with wide color spaces such as BT.2020,
- Compatible with color sampling up to 4:4:4.
DPL Labs certifications
Completely independent of manufacturers and the HDMI Forum, DPL Labs also offers a series of state-of-the-art tests to evaluate the UHD 4K performance of an HDMI cable with the highest possible accuracy. Through this comprehensive set of tests, engineers at DPL Labs subject HDMI cables to a veritable torture session. Only the best HDMI cables showing performance beyond the minimum requirements of DPL Labs are certified. This is your guarantee that an HDMI cable will deliver the best possible performance for a long time to come. High-end HDMI cables from some manufacturers have been successfully tested, including Kordz HDMI cables, Nordost HDMI cables and Wireworld HDMI cables.
HDMI cables that pass DPL Labs tests are classified into two categories:
HDMI DPL 4K 10.2G Certification
Compatibility with 1080p 50/60p and 4K video streams up to 50/60p (8-bit), certified bandwidth up to 10.2 Gbps :
- 1080p @ 50/60p, 8/10/12/16 bits, RGB/YCbCr 4:4:4
- 4K 2160p @ 30p, 8/10/12 bits, YCbCr 4:2:2
- 4K 2160p @ 30p, 8 bit, RGB/YCbCr 4:4:4
- 4K 2160p @ 50/60p, 8 bits, YCbCr 4:2:0
HDMI DPL 4K 18G DC certification
Support for 1080p 50/60p and 4K video streams up to 50/60p (8/10/12/16 bits), certified bandwidth up to 18 Gbps, Deep Color support:
- 1080p @ 50/60p, 8/10/12/16 bits, RGB/YCbCr 4:4:4
- 4K 2160p @ 24/25/30p, 8/10/12/16 bits, YCbCr 4:2:2
- 4K 2160p @ 24/25/30p, 8 bits, RGB/YCbCr 4:4:4
- 4K 2160p @ 50/60p, 8/10/12/16 bits, YCbCr 4:2:0
- 4K 2160p @ 50/60p, 8/10/12/16 bits, YCbCr 4:2:2
- 4K 2160p @ 50/60p, 8 bits, RGB/YCbCr 4:4:4
