Videography March 1998
Getting Digital and Analog
to Play Together
By Sheldon Liebman
Its Video. Its Data. Its Analog. Its Digital. Sounds like something out of the movie "Chinatown," but in fact its a description of what every video facility is facing today (or will be facing very soon). Back in the "good old days," when everything was analog, it was easy to move signals around a facility. Video here, audio there, control signals everywhere, all being operated from a single interface that was smart enough to keep you out of trouble.
Today, the situation has become much more complicated. In a sense, computer networks have an easier time of it than video networks. On a computer network, every station is capable of both sending and receiving. As long as theyre all equipped with the same type of network card and driver as the hub, everyone can send to or get from everyone else. In virtually all cases, the data gets where its going without becoming corrupted.
Are We Compatible?
What you do with the data is something else again. Once you receive a file, you need to have the proper software on your machine to make use of it. File compatibility has been a large part of computer networks for many years, so lots of effort has been put into this area. How many types of files can you import to an Avid? How many formats can you export from 3D Studio Max? Before new software is added to an existing environment, somebody usually checks to be certain that it can work with the software thats already installed.
Video, on the other hand, has traditionally been reduced to the lowest common denominator composite analog. Need to get something off a Digital BetaCam? Use the composite output. Source images on a computer? Scan convert the output and feed it into the switcher. In virtually every case, the result was destined to be viewed or broadcast as a composite analog signal anyway.
Now, however, things are really changing. The number of advanced television formats that are available is staggering. Pretty soon, it wont be possible to fall back on composite analog NTSC because the ultimate audience wont be viewing it that way. Progressive scan and interlaced video must coexist. Multiple resolutions must be supported. And there needs to be a way to move it all around together and mix it together.
Going back to the computer side, its easy to mix formats. As the files move around, the network has no idea whether they contain MPEG, JPEG, or still image data. Its just moving bits and bytes. File formats and software viewers support multiple resolutions and play them back on standard computer monitors. Need to composite one resolution over another? Software can scale one or both to the desired output size and then merge them. Usually, this isnt done in real-time, but at least it can get done.
Lets Tie One On
One of the major reasons data can be combined on the computer side is that its always digital. An individual computer might accept analog input or create analog output, but those inputs and outputs are separate from the actual data network used to move information between machines. On the video side, older equipment takes analog in and puts analog out. Even if the video is processed internally in some type of digital format, the only connections with the outside world are analog.
This means there must be an analog network in a facility to handle these signals. As newer equipment has been purchased, many facilities have created separate networks that allow signals to be moved around digitally. One example we covered recently is Crawford Digital in Atlanta.
In their new facility, everything is moved around as a digital signal. Analog information that needs to come into this network is immediately converted to digital. At the very end, an analog version can be output. During the project, however, it all stays digital.
Linking digital and analog networks together has become critical for many facilities. This is done through a process called "Tieline Management." If one analog device needs to be connected to one digital device for playback and recording in both directions, two additional pieces of equipment are needed. One is a D/A Converter (digital to analog) and the other is an A/D Converter (analog to digital). Since most video equipment is connected through a routing switcher, a pair of converters can be hooked up between two routers (one analog and one digital) to create a bridge between these two worlds. If only one stream at a time needs to be handled, one pair can be used. For more simultaneous access, more bridges can be built.
Just having the bridges isnt enough to make this happen. It also requires cooperation from the control system software being used. The analog network software, for example, must know that there is an A/D converter on output "A." The digital network software must know that this digital stream is connected to input "X." If you need to record from analog VTR 1 onto digital VTR 2, the software systems will make sure that VTR 1 is connected to output "A" and that VTR 2 connects to input "X."
If you need more than one bridge, the process can quickly become bogged down unless the two control systems can speak to each other. To address this issue, both routing switchers and control software are evolving.
On the software side, control systems are being used with protocol converters. With one of these boxes sitting between the control system from Company "A" and the routing switcher from Company "B," all the commands are converted to the proper format. In this way, the control system just thinks its dealing with many of its own routers. One example of this is from Pro-Bel America, a Chyron company. Their System 3 Matrix product uses protocol converters to link different types of routing switchers from a variety of companies.
On the hardware side, new routing switchers are becoming available that mix analog and digital signals in a single footprint. PESAs new Tiger product, introduced this month, accepts both 60 MHz analog and SMPTE 259M digital cards in the same frame. The companys WIN3500 System Controllers manage the whole process and include Tieline Management capability.
Hoping for Resolution
Moving between analog and digital formats isnt easy, but people have been doing it for the past few years. Dealing with the possibilities of multiple resolutions, however, is a completely new issue. Before the standards were set, nobody tried to create a single facility that intermixed HDTV (High Definition Television) and SDTV (Standard Definition Television). Now that the standards are in place, though, people are trying to determine how many different networks need to exist to handle everything.
The biggest problem with handling multiple resolutions is that it requires handling multiple data rates. Todays routers are designed to handle up to 360 Megabits per second (Mbps) of data. At this rate, CCIR601 video can be moved around easily. HDTV signals as defined in the new standards, whether 1080I (interlaced) or 720P (progressive), require up to 1.5 Gigabits per second (Gbps) of bandwidth, or approximately four times the current limit.
Since uncompressed HDTV is approximately four times the bandwidth of uncompressed SDTV, some companies are choosing to move this high-resolution information around by using four standard resolution connections. In the Crawford Digital article mentioned above, Pluto Technologies pointed out that they can stack four HyperSPACE units together to handle uncompressed HD applications. For 480P60, a progressive scan version of traditional NTSC, two units can be hooked together.
In a routing switcher environment, upgraded control software may be able to link sets of four inputs and outputs the same way it can perform Tieline Management. If compressed HD is used (at a 4:1 compression ratio), the signal can even be routed through a single input and output port.
Coming Soon More
The best solution to the bandwidth requirements of HDTV is to get equipment that is designed from the ground up to handle it. Squeezing these signals through existing hardware and software may work for the short term, but its clearly not a long-term solution. Upgrading any facility to handle the new ATV formats requires a significant investment in new cameras, recorders, transmitters, etc. New control systems and routing switchers just need to be added to that list.
At this years NAB, well be getting our first look at the next generation of products that are designed to deal with multiple and/or high definition video formats. And this isnt just multiple resolutions, but compressed and uncompressed versions of these resolutions.
Transmitting HDTV signals from a network to an affiliate, for example, isnt likely to happen at 1.5 Gbps. It is more probably that it will be compressed and sent as MPEG-2 data at a reduced data rate. How low can that data rate go? Thats part of the discussion thats going on. If a station needs to add information over the signal like a logo or emergency weather information, its important that the signal can be rebuilt to full resolution without too much degradation.
Whatever data rates are used, the signals are going to need to move in, out and through a facility in some manner. Newer routing switchers and control systems will work together to address these issues.
One product that has been announced is the PESA Alliance Master Control Switcher, which is designed to support both SDTV and HDTV broadcasting. The product is a joint effort between PESA Switching Systems, Inc. and the Broadcast Equipment Division of NEC America, Inc. Based on NECs "Multi-Format Technology," the PESA Alliance will be shown as an engineering prototype at NAB and is scheduled to ship before the end of 1998.
In its basic form, the Alliance can handle two channels of SDTV or one channel of HDTV. It can accommodate various progressive and interlace HDTV standards and can be used for full-time SDTV, full-time HDTV or a mixture of SDTV and HDTV broadcasting.
On the routing side, Pro-Bel America will be showing a prototype of an as yet unnamed HDTV router. It will be demonstrated as part of the Harris/PBS DTV Express truck in the outdoor exhibit area.
Making the Right Connections
Neither of these products solves all the issues associated with multiple formats. Weve moved from a time when there was an analog video network, to the existence of both analog and digital networks, to a future that will add at least one HDTV network to the mix. And they all need to be connected in some way.
If compressed signals need to be rebuilt to full resolution, perhaps a single piece of equipment can be inserted that accepts the compressed signal and outputs an uncompressed signal into an existing network. If the signal needs to stay compressed, however, another network may need to be built that is designed to operate on the signal without changing its compression ratio or data rate.
Each format that a facility wants will probably need its own network, with converters sprinkled all over the place to be used as bridges from one format to another. In this type of scenario, control software will have to become extremely sophisticated to handle all the possibilities. Todays Tieline Management issues will seem incredibly simple compared to the requirements of these systems.
Imagine taking a compressed HD source, turning it into both uncompressed HD and CCIR601 signals, keying station identifiers over the top and then transmitting both results simultaneously over the air. In a simpler case, there may just be a source in one format that needs to be manipulated and converted to another format. Depending on what equipment needs to be used for which functions, it may still need to move between many formats on the journey from source to target.
If real-time results are required, its clear that multiple networks need to coexist under a single control system. But what if we arent in a real-time environment? In this case, the convergence of computers and video may be the answer.
One input for every format. One output for every format. In the middle, software that can change resolutions and process single or multiple streams of data. But now, instead of using the lowest common denominator, perhaps well use the highest. Turn everything into uncompressed HDTV format, process it all at that resolution, then output the end result in whatever format we need.
Video networks werent designed for digital data, but this is exactly what computer networks do best. Perhaps the best way to move forward, at least outside of the actual broadcasting scenario, is to play off the strengths of each. If we do, the issues of digital versus analog, compressed versus uncompressed and HDTV versus SDTV may seem a lot more manageable.
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