4K signal distribution11 February 2015
System integrators have become accustomed to using high-definition AV signal extenders and switches to transmit audiovisual signals over long distances using CatX or fibre cabling in both commercial and residential installations. These are essential pieces of equipment to overcome the minuscule lengths of cable that native HDMI and DVI signals can be carried.
The anticipated popularity of 4K video presents manufacturers and installers with new challenges: new equipment and/or techniques are needed to transport 4K UHDTV over these longer distances.
The problem lies in the enormous bandwidth required to handle 4K video at the highest levels of quality and frame rate. The current HD interface standard, HDMI 1.4, is capable of reaching the high resolution of 4K TV, but at a frame rate of 30Hz and with reduced chroma subsampling. Greater bandwidth, of 18Gbps and above, is required to fully manage true UHDTV at its higher levels of quality. This is addressed by the HDMI 2.0 and large screen displays with HDMI 2.0 ports are just becoming available from the larger manufacturers.
Distribution of 4K signals is another matter entirely. While CatX and fibre cables are theoretically capable of transmitting the higher bandwidth signals, there are currently no devices, or even chipsets capable of translating full bandwidth signals into a form necessary for transmission. HDBaseT, the most widely used connectivity standard, has a processing bandwidth of 10Gbps which is adequate for uncompressed transmission of HD and the lower levels of 4K video, but falls short of the necessary 18Gbps for full 60 frames per second 4:4:4 video.
According to Sandra Welfeld of the HDBaseT Alliance: “HDBaseT is a viable and proven alternative for 4K transmission. As of now, the new specification of the HDBaseT standard can transmit 4K, 60fps, at 4:2:0 and 4K, 30fps, at 4:4:4, which is compatible with most of the content being generated now at 4K. Our plan is to double the bandwidth so that 4K, 60fps, 4:4:4 will also be supported, if, and when the content is available.
“The lack of 4K content is more of an issue than equipment. There are many 4K displays available already, and prices are coming down every day. Content, on the other hand, has come a bit slower. However 4K brings such a leap in viewing quality, that we believe it’s just a matter of time until most content will be produced at that level, both for entertainment and commercial purposes. If anything, the fact that HDBaseT is a cost-effective option for 4K delivery is a driver for more 4K products in the pro-AV sector, as a report from FutureSource pointed out.”
Technically, it is possible and viable to transmit true UHDTV signals. Aptovision’s BlueRiver NT uses two CatX cables or a single fibre to accommodate the enormous bandwidth. “Alongside the capability of 4K 60Hz (4:4:4) transmission, BlueRiver eliminates the need for custom AV cross-point switches and allows the use of off-the-shelf Ethernet switches instead. So with the emergence of 40Gbps and 100Gbps switches there will likely be a move for AV distribution to the Ethernet platform,” says Welfeld.
For now, 4K transmission equipment is available that can handle available source and display devices at a resolution that is acceptable to viewers. Whether or not there will be a demand for better solutions is questionable, as Welfeld points out: “Experts in the industry today expect most 4K content to stick to 24fps, 4:2:0, for the foreseeable future, because the human eye cannot detect the difference in anything better, in any normal viewing distance, be it on a living room or in a movie theatre, and there is not yet economic justification to go any higher than that”.
The industry is undecided.