We present the latest technologies in cables and connectors, owing to their pivotal role in the transmission of data in the broadcast business
By Anisha Gakhar
Cables play a key role in the broadcast of audio and video, by annexing themselves to devices with the help of connectors. These help the respective devices perform its broadcasting function effectively. The selection of appropriate cables and their connectors, dwells on the elements that influence the utilisation of existing cables and the planning and installation thereof to ensure a cost-effective and future-proof solution in a business where everything is gradually moving to the cloud.
Cables and connectors are an integral part of the broadcast set-up, since they facilitate the means by which the information signal transmits from one device to another. The often-overlooked peripherals carry more importance in a broadcast system as they affect the quality of video and audio signals.
Dilip Kathuria, CEO, CDM Technologies and Solutions, said, “To imagine a world without cables and connectors is analogous to life stranded at a single point.”
High Definition Multimedia Interface (HDMI) has been gaining widespread acceptance as a cross-over technology, owing to their ability to convey data digitally between devices. Like USB connections, HDMI connectors are usually on the edge of a circuit board, and thus, they don’t lock. . The lack of a lock can provide a certain margin of safety.
Many broadcast companies are migrating to fibre optics, for their cable needs. One of the main benefits of this technology is that it offers a large bandwidth, over longer distances, along with a better signal-to-noise ratio. It demonstrates immunity to interference and reduced size and weight. The main applications of fibre optics are HDTV camera links, audio and video set-ups, broadcasting studios and newsrooms. According to industry experts, the key factors to determine the usage of fibre optics are whether one needs a single or multi-mode cable, the quantity required and its networking.
They also said that one of the primary rationals for the industry’s transition to digital television is high-definition television (HDTV). This transmission standard incorporates up to six times more data than conventional television signals and twice the picture resolution. The high resolution makes HDTV images more lucid and picturesque as compared to those produced by traditional formats, with the help of five channels of CD-quality audio. HDTV images have a 16-to-9 aspect ratio (the ratio of width to height), providing wider images than the primitive 4-to-3 ratio.
While HD-SDI is a global standard, the emergence of 3G-SDI technology as a worthy successor to this interface has revolutionised the way the broadcast industry perceives data communication, for their main feeds as well as backups.
CABLES THE INDUSTRY IS INVESTING IN
According to Kathuria, there are three principal factors to consider before zeroing-in on a cable-connector set. These are the center conductor, cable insulation and the shielding of the connector. Each factor has a set of pros and cons, which form an essential basis of selection of the right alternative. The center conductor of a co-axial cable is of two types, solid and stranded. Stranded is a more flexible option and therefore, the preferred choice for outdoor and stage use. The insulation can be solid, foamed or highly-foamed. Foamed and highly-foamed insulations have a better attenuation, which makes them a good choice for HD videos. As these insulations contain air physically, they are weak in external pressure; making it imperative to pay attention to where and how the cables are installed.
Shielding usually includes is usually a braiding with or without aluminium foil. These are further categorised as single, double or triple layered; and are made of either bare copper or tinned copper. The ones braided with aluminium foil are not suitable for bending and mobile applications, unlike the plain braided ones.
Kathuria added, “Propagation Delay (time required for a signal transmitted from one end of connection to another) is an important factor that should be considered before final selection of the cable.”
3G-SDI TECHNOLOGY – A FORE-RUNNER
Lately, the demand for transmitting high quality videos with higher definition, brightness and swift motions in the broadcast industry has risen considerably. Severeal industry experts believe that serial digital interface (SDI), a family of digital video interfaces standardised by SMPTE (The Society of Motion Picture and Television Engineers), is increasingly being used for broadcast-grade video. The SMPTE has described three mapping schemes for transporting uncompressed video and ancillary data like audio data, the audio control packets, the payload ID and the time code into a serial digital interface operating at a nominal rate of 3 Gbit/s. These are defined by three levels:
According to the Ebu technical report, the Level A definition is the direct mapping of an uncompressed 1080p/50 video stream into a serial digital interface operating at a nominal rate of 3 Gbit/s. Level B-Dual Link (B-DL) is the dual-link mapping of a 1080p/50 video stream into a serial digital interface operating at a nominal rate of 3 Gbit/s. The design is expected to be robust if one format (Level A or Level B-DL) is used throughout.
The Level B Dual Stream (B-DS) is the dual-stream mapping of two independent 1080i/25 (or 1080p/25) video streams into a single serial digital interface operating at a nominal rate of 3 Gbit/s. It carries two 1.5G-SDI streams on a single co-axial cable and while the ITU and SMPTE are discussing standards, Level B-DS is being used by some organisations to carry the left and right eye signals of stereoscopic 3DTV. Although, Level B-DL carries 1.5Gb/s signals, it is subject to the same 3Gb/s installation requirements as Level A and Level B-DL.
Industry professionals who do not wish to be named, said that the ITU-R BT.656 and SMPTE 259M defined digital video interfaces used for a relative standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s.
3G-SDI projection is expected to be followed by SMPTE established transmission standard, 12G-SDI, which has greater transmission capacity than 3G-SDI, and is compatible with 4K.
HD-SDI VS 3G-SDI
Whilst weighing which option to go ahead with, specifications that add utmost value to the selection should be chosen with care. HD-SDI is standardised in SMPTE292M, at a 1.5 Gb/s interface, the bit rates supported by HD-SDI are actually 1.485 Gb/s and 1.485 / 1.001 Gb/s. Most existing HD-SDI displays in the legacy systems can be used with high-resolution cameras, after checking the compatibility. Also, it is a plug-and-play solution, and thus, can be used to create a simple surveillance system. It deploys long distance cable lengths that are typically above 100m. A 3G-SDI interface requires a computer as a mediator between the camera and the monitor, where as a HD-SDI provides a direct connection between the camera and the display.
On the other hand, the use of 3G-SDI within a broadcast environment, serves the ability to send numerous different video formats, production and digital cinema formats down a single wire. 3G-SDI is an upgraded version of HD-SDI. The system supports SMPTE424M, SMPTE292M, SMPTE259M, SMPTE297M, SMPTE305M, and SMPTE310M standards. Using dual 3G-SDI, one can transport a full 12-bit 4:4:4 or RGB 1080p60 feed with space, for audio and metadata.
The development of HDTV formats such as HD-SDI and 3G-SDI were designed to encode digital video as a single signal that combines serialised data and clock reference. The use of high data rates such as 1.485 Gb/s for HD-SDI and 2.970 G/s for 3G-SDI, long cable lengths and the encoding methods are some features common to both.
THE YES AND NO
The world of cables and connectors may seem daunting, but the task can simplified keeping a few pointers in mind. A broadcast company should be cautious to use video cables for video and separate audio cables for audio, without interchanging the two. It is a smart choice to buy the right length for the right application. Long cables expose the system to hostile forces, which might in turn lead to an outage. Portable situations call for flexible cables and more rigid ones for permanent installations.
The connectors can be chosen by specifications like strand/single strand connectors, foil/mesh shielding, crimped/molded ends. The choice depends on the area of application, in many cases. Molded cables enable strain-relief to the connections, but come in the expensive category. Also, it is irreparable in cases of wear and tear. Crimped ends on cables have metal rings and cable insertion points squeezed tightly around the ends of the cable, making them susceptible to getting loose.
The selection of the best-suited combination of cables and connectors can go a long way in enriching one’s production quality, which will eventually boast of crisp, colourful visuals and crystal clear audio. Connect, for good!