Intercom systems
Feb 1, 2008 12:00 PM, BY JOHN LUFF
Spectrum auctions threaten to interfere with broadcast and sports communications.
There are three types of communication that can convey complex information: written, visual (i.e. video) and spoken. In complex tasks, such as managing real-time operations in a broadcast production, the first two are pretty impractical.
Annotated scripts provide a basis for managing the planned flow of a production. When things change, the first thing we do after analyzing the steps needed to keep things on track is speak to the rest of the production team. How we do that is an interesting topic.
The history of voice communication
Voice communication was enabled largely by the invention, about 130 years ago, of the carbon microphone. The invention was claimed by both Thomas Edison in March 1878 and Emile Berliner, who separately filed related patent applications in June 1877 and August 1879. The premise behind a carbon microphone is quite simple, with carbon granules placed between two metal plates. Sound waves cause compaction of the carbon, changing the resistance and thus converting sound waves to voltage fluctuations. We have all seen pictures of phone operators with uncomfortable headsets, which remarkably were still in wide use in our industry well into the later part of the 20
By connecting a microphone and a small speaker, the audio is propagated over an indeterminate distance, perhaps to the professional sitting next to us, or at a considerable distance. In simple intercom systems, all parties speak and listen on one circuit, not surprisingly like early telephone systems.
In carbon microphones, carbon granules are placed between two metal plates. Sound waves cause the carbon to compact, which changes the resistance. This converts sound waves to voltage fluctuations.
Often called PL, for party line or private line, intercom systems evolved little until complex productions required multiple lines with selectable talk and listen capability for all participants. For example, in the 1970s when RTS Systems, now a part of Telex, introduced sophisticated four-wire and two-wire systems such as the 802 Master Station, it raised the bar considerably. But as much as things changed, they remain the same in many ways today.
In Europe, four-wire communication has been prevalent for many years. When I first worked with the European Broadcasting Union (EBU) in 1980, it was already operating a multinational intercom system of four-wire circuits connecting control rooms in every Western European television station. I remember marveling at the ability to speak to London and Moscow from Detroit during the Republican Convention. This was no small feat, considering it was built using analog audio circuits deployed on multiple national carriers' systems, which of course used varying audio levels.
In the United States, you had to order two pairs individually to accomplish this, one for send and one for receive. Then you had to manage the levels and connections yourself.
The EBU still maintains complex communications systems, though now they are digital.
Modern intercom systems
Lately, much of the world's intercom systems have evolved into complex amalgams of both two-wire and matrix four-wire systems. A two-wire intercom is appealing because of its simplicity, with the power supplied across the pair that also carries send and receive audio. Local side-tone cancelling keeps the system from becoming an effective feedback loop. Often, two-wire systems are built on standard audio cabling, with the third wire carrying a second channel. Of course if mistakes are made, you can fry a microphone by plugging it into intercom circuits, which requires some thoughtful selection of connector sex and labeling.
Four-wire matrix intercom systems are mostly digital today. This allows complex programming and control over the volume in each crosspoint combination. It also allows setup and teardown of circuits with alacrity, or the capriciousness of the head of production. The ability to store setups, including the keys available on individual control panels, is critical to making a system flexible.
A normal newscast might require only six to 10 personnel, who could all use one circuit. But on election night, the number of private circuits and personnel explode. As individual remotes are set up, they can be added to existing circuits and later dropped off when finished from a setup station that often has graphical representations of the system configuration.
Modern systems include remote user stations with active buttons and displays connected to a complex matrix. In many manufacturers' implementations, individual matrices can be connected together over extended distances to expand systems to multiple studios, or even multiple cities. With VoIP, MADI and proprietary interconnection schemes, almost any size system can be accommodated. Major news organizations have extended studio intercom systems to transportable earth stations using satellite deployment of communications systems, including IFB, telephone and data services. By doing so, they integrate field operations — often from primitive conditions — into the production as if they were simply down the hall.
White-space dilemma
There are times when using a wired intercom does not work. We have become accustomed to using cell phones with Bluetooth headsets, which in no small measure achieves the same level of sophisticated communications that complex intercom systems provide in the closed loop. Any wireless communication comes with the propagation challenge. Four-wire systems extended by radio enable roving cameras, floor directors and other production assistants to do their tasks untethered.
These communications channels are threatened by the momentum behind white-space devices, which the FCC seeks to authorize on unused television channels. This is the same space that wireless microphones and intercom systems use. Many people are not convinced that these digital communications systems, which self-test spectrum use before transmitting, will actually work.
At the very least, the potential to affect field and studio wireless communications systems is real. The SBE and manufacturers of systems used for broadcast and sports pushed hard to have prototypes tested during the 2007 and 2008 NFL season in the harsh environment of live football games. The FCC did not organize tests, but keep looking for information. A lack of effective spectrum management could make wireless intercom and IFB much more difficult to manage.
John Luff is a broadcast technology consultant.
Send questions and comments to: john.luff@penton.com
| Want to use this article? Click here for options! |  |
