Sending Successful Video Signals

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As consumers living in the 21st century, we are almost constantly surrounded by video displays. Video has become an extremely popular and effective communication platform and is widely used for a large variety of purposes. Apart from cinemas and television broadcasts, people share many things from news, social media content and product marketing to showcasing talent. Whether the talent is amateur or professional, the same video platform is utilised. The consuming audience experiences all this by watching a video screen showing video content, but behind the scenes, from a professional AV perspective, it’s an entirely different ball game.

Every video system has three elementary components which comprise the system. There are the source devices, the sync devices and the connection between the two endpoints to complete the link.A source device is similar to the ‘start’ point of the particular system’s signal. This is the device that outputs or produces the video signal and it could be various different components. The most common examples are DVD or media players, personal computers and computer servers with video output ports. Another popular example of a source device is a video camera, producing and transmitting a video signal. The sync devices form the other end of the line and they are the video screens on which the playing video file is viewed. Multiple technologies are used to display video such as television screens, modular LED panels (digital billboards or big screens at sport events and concerts) and video projectors which project light onto a reflective display surface. The latter is very common in presentation venues, cinemas, auditoriums and concert stages. The connection between these endpoints is where the challenge lies.

At home it might seem like a really simple task to connect a DVD player to a television with an HDMI cable and Bob, as they say, is your uncle. In the professional video industry, systems can be a lot more complex depending on the application. Some systems require more than one video source to be routed to a single display as used in boardrooms with multiple connection points. Others require a single source to be distributed to multiple display screens similar to systems in airports and shopping centres. Apart from these there are systems that require both of the above in one solution, i.e. multiple sources to be routed to multiple displays at any desired configuration. This also requires the functionality to manipulate a current configuration and reroute any source to any screen or screens, with the press of a button. The above challenges are all doable as equipment is readily available to meet these needs as long as the video designer understands the system architecture. Accurate design will ensure that the correct components are used and configured accordingly. The users can then take charge and create configurations however they desire. As mentioned, the real challenges lie in the connection between source components and display screens. Systems such as these are mostly based on unique requirements and are designed to provide custom solutions in response. Therefore the challenges that accompany signal distribution are not exactly black and white.

Video signals are based on analogue waves which are transmitted over a specific medium, such as copper and fibre cables. Depending on the format, and the resolution of the video signal being sent, there are distance limitations. Over longer distances, the physical environment causes signals to weaken until they are no longer viable for video reproduction. Within analogue signals such as RGBHV (Computer graphics or VGA) or composite video (standard definition video from a player or camera) for example, the amplitude of the physical wave is what is important. A transmitted signal’s energy will decline as it travels further along a cable. An additional challenge is the fact that radio waves constantly exist in the air all around us, which then interfere with the cable and transmitted signal. This is called radio noise and although this noise is mostly fairly weak, it does cause interference. As radio noise exists everywhere, the interference happens across the entire length of a cable and the noise is continuously present anywhere on that cable. This phenomenon is known as the noise floor of a radio signal.

Coaxial cables, used for analogue signal distribution, are designed with a thick copper core and a foil or wire strand braiding around the outer diameter. This cable design functions as a Faraday cage and effectively reduces noise interference. The noise, however cannot be eliminated entirely. Thus from the available amplitude of the original signal, one can only utilise the section superior to the noise floor. This section is known as the signal-to-noise-ratio and needs to be sufficient enough in order for the video to be reproduced. Analogue signals can be amplified to increase amplitude or rather increased wave size. This is done in an attempt to have the waves travel longer distances. In some circumstances, the amplifying component cannot distinguish between the video signal and the noise floor and as a result it amplifies all the waves present on the cable and produces an increase in signal amplitude as well as an equal increase in the noise floor. The result is that the signal-to-noise-ratio remains unchanged. Due to this phenomenon, successful amplification needs to be applied nearer to the source where the signal-to-noise-ratio is still sufficient. Once it is no longer adequate, the signal will be present but not clear and would not suffice for video reproduction.

Certain applications require video transmission over such large distances that constant amplification fails to qualify as a viable solution. Balun technology was developed to extend signal ranges. The architecture requires a transmitter and receiver with a CAT cable in between. Baluns – a name derived from the terms balanced and unbalanced – uses technology similar to balanced audio systems where the video signal is duplicated at the transmitter end and both signals are sent over multiple twisted pair cables to the receiver end. The only difference between the two is that the second signal’s frequency is inversed to a negative version of the first. The noise floor, however, cannot be manipulated and thus remains constant and equal on both signals. The receiver end then collects from the two signal feeds, a positive video signal, a negative video signal, and two X positive noise floors signals. All of these are compared and all matching signals – in this case only the noise – gets eliminated, leaving only the two X video signals of which the positive one is used, noise free.

In the digital world things work a bit differently. Digital video is not the only component to be distributed. Many formats exist such as DVI and SDI to cater for different applications but HDMI is the most common signal for High Definition digital video distribution. However it’s not video alone but rather a multi-media format which hosts a collection of additional signals such as audio feeds, power, Ethernet, EDID (Extended Display Identification Data) which is used to automatically identify a matching, optimum resolution between a source and a display, and lastly HDCP (High-definition Digital Content Protection), a protocol initiated by film producers which prohibits end users from duplicating copyrighted content. This is a large amount of information to be transported and the distance limitations are much bigger than with analogue video.

A digital video signal is still an analogue wave but the polarity is manipulated to be either positive or negative. A positive wave represents a 1 and a negative wave represents a 0. In a previous article I explained how the analogue metric information is converted to a binary string. Binary numbers consist out of only 1s and 0s and the strings can thus be sent over larger distances. The receiving end collects the strings with 1s and 0s and reconstructs the information prior to being converted back to analogue signals, for human beings to comprehend. The noise floor is still present but the signal-to-noise ratio is irrelevant as the receiver only needs to establish whether a wave’s amplitude is positive or negative in order to identify the strings.Thus no information is lost. Unfortunately though as soon as the signal is interrupted or becomes too weak and it loses as much as a single digit, the strings become corrupted and initial information cannot be established, nor reproduced. The entire signal is then obsolete. In other words, a digital signal works 100% or 0%. There is no in-between. This is known as the ‘cliff-effect’.

In spite of this amazing technology, HDMI is still limited and as soon as a cable exceeds 15m, an alternative solution is required to distribute the signal. The beauty of these challenges within the current technologies is that they receive a lot of attention and funding. Solution focused technologies are constantly seeing the light of day. Range extenders similar to baluns exist and are a popular solution. A few years back, HDBaseT was introduced to distribute HD digital video. HDbaseT uses high quality Cat5e and up to distribute media signals, control signals and electricity to power equipment (depending on their consumption) all over one cable. HDBaseT technology was really well received and many display manufacturers invested to get their products to accept HDBaseT as an input, thus eliminating the receiving component of the HDBaseT distribution system. A further popular way to extend digital signals is to use fibre systems instead of copper. Fibre transmitters send light along a fibre pipe or cable at much longer distances than copper because of the lower resistance. The same strings containing 1s and 0s are sent and the same principle applies at the receiver end.

The latest and greatest form of distributing video (and media signals) is to convert them to IP packets and distribute them over an IP network. The world is full of IP networks and in principle it makes sense to simply connect to a network and introduce the media signal to the network and then collect it anywhere else on the same network, or even at multiple places, at different times. This great idea was halted as soon as the bandwidth requirements became evident. Video has been streamed over networks for many years but it has had to be compressed to such a low quality in order to make it viable to send and download. Like anything in today’s world the technology caught on and video over IP is becoming more and more available. Technology even exists to distribute 4K resolution uncompressed, that still supports HDCP. Due to of the massive amounts of bandwidth required, the network limitations needs to be 10Gbps – which is not excessive anymore. Slowly but surely the IT world will upgrade networks to 10Gbps. The only other obstacle for video over IP systems is to convince the IT managers and network-security teams. The latter might be the biggest challenge but it will have to be addressed.

 

Video distribution has come a long and innovative way to where it is today. The current pace of technology development is unlikely to slow down. The near future is leaning towards integrating into existing IT technology which will then form the backbone to all our communication needs. But then again, who knows what the future holds?