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MillimeterLocation Wireless
May 1, 2002 12:00 PM, By Philip De Lancie
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 David Boyll operates the boom in San Francisco’s Golden Gate Park for a national spot for Dr. Scholl’s. |
Once exotic and remarkable, wireless audio has long been accepted into the standard toolbox of audio professionals. Used properly, today's wireless setups offer freedom and mobility while maintaining the fidelity of the captured sound. But while the quality and reliability of wireless sound are much improved, there's still an art to using the technology on location without leaving a shoot vulnerable to problems — particularly interference — that can potentially result in calamity. What follows is a set of guidelines for this art, based on feedback from a half-dozen sound professionals who make their living in the field.
Consider the alternatives
Before figuring out how best to approach a particular project using wireless, first consider whether wireless is truly called for at all. That's the advice of San Francisco freelancer David Boyll, a sound mixer, boom operator, and tape operator for broadcast/cable, commercials, corporate television, infomercials, sports, and feature films. Boyll says that often the notion that wireless is needed originates with a field producer who hasn't necessarily thought through other possibilities.
“Only use wireless mics when no other method will work,” Boyll says. “If I get my way, which happens about 75% of the time, I prefer to boom all location sound. It's easier, matches better shot-to-shot, and there are fewer pitfalls. Of course, this requires a separate, experienced sound person and the proper equipment.”
In other situations, of course, wireless may be a lifesaver. Steve Osmon of Austin, Texas, whose location sound work ranges from documentary and corporate production to ENG for major networks, offers the example of small, one-on-one interviews where portable stand lighting will be used. “Check to see if the person doing the lighting will be using any type of dimmers or fluorescent tube-type equipment that could create audio interference,” Osmon says. “If they are, plan on going wireless, because nine times out of 10 if you try hard-wired microphones in the presence of lighting dimmers or lighting that requires the use of a ballast, you will encounter hum in the audio. Using a quality wireless system will eliminate that hum.”
 Bob Charlap and fellow freelancer Didi Hill work the 2000 World Series for Fox Sports at Shea Stadium, the home of Major League Baseball’s New York Mets. |
Osmon also points out that applications of wireless systems on location include not only wireless microphones, but also wireless retransmission of audio from a mixer to a camera. “At one corporate convention,” he says, “I was tied down by a hardwire audio cable to a house mixing board, but the cameraman wanted to be able to roam the room and still pick up ‘house’ audio. So I hooked a wireless transmitter to the main output of my mixer and attached the receiver to the camera. The important thing to remember is that the cameraman must always be able to monitor the audio out of the camera with headphones or ‘ear buds’ to make sure there are no interference hits in the wireless link.”
Do your homework
While many recordists like to rely on a basic kit of their own gear, when it comes to wireless the variables are such that rental is often the preferred solution. But the trick is to rent the right tools for the job, and that means finding out as much as possible in advance about both the type of shoot and the setting.
“Wireless needs vary from job to job,” says Osmon, “so quite a few sound mixers rent equipment on an as-needed basis depending on the assignment. Therefore it makes sense to find out what the job will entail ahead of time. You can avoid renting a couple of high-end UHF diversity units when a less-expensive VHF unit with a single transmitter and receiver would work just as well.”
Osmon also suggests talking to the director of photography prior to the shoot about plans for camera placement in the room, particularly if the shoot calls for multiple cameras and you plan wireless links. And he adds that if you plan to take a wireless feed from a house system, advance coordination with the house A/V company is also imperative. “Most wireless systems require a mic-level feed of -60dB. Anything hotter than -40db and you risk damaging the transmitter or distorting the signal generated by the mixing board. But most house boards only offer a line level or +4dB output. So some sort of padding [attenuation] of the signal will be needed for you to plug in your wireless system.”
Learn the location
Another aspect of advance preparation is becoming familiar with the location itself, particularly determining if there are any systems in place that might present a problem for wireless use. “With advent of digital television and digital two-way radio networks,” Osmon says, “there is greater concern for interference with wireless microphone systems. I have learned my lesson about working in cities that I am not familiar with and encountering interference from a television station's digital transmitter, or working in an office building or manufacturing facility where there is digital paging or a two-way radio system in place.” As a starting point for avoiding such digital interference, Osmon suggests referring to resources on the Web that list broadcast frequencies used in a given city, allowing you to compare them with those used by your wireless equipment.
 Nick Kolias on location for a documentary about elephant seals on California’s San Miguel Island. |
In some cases, Osmon says, it may not be possible to use wireless equipment at all because it would interfere with equipment being used at a facility, such as a hospital or a construction site with explosives using electronic detonators. He recommends checking ahead about possible restrictions on wireless use.
Find your frequency
When you're relying on wireless, a frequency with interference is as bad as a mic cable with a faulty connection. So a top priority is finding an open channel with a clean signal. Boyll says that checking all frequencies for interference is especially critical now that DTV is off the ground and the spectrum is getting crowded with more wireless mic users.
A big help in this regard, if you've got the equipment to do it, is to scan the location for possible frequency problems. “I always bring my Sony Wavehawk Scanner when going to a new city,” says Todd Johnson, a New York-based sound recordist who works shoots for network magazines, news, documentaries, sports, and corporate projects. “Before the shoot I will use the scanner at the location to see if anybody else is using the same frequencies I do. If I find interference, I can either change transmitters or the frequencies they are set to.”
To change frequencies, of course, you need a “frequency-agile” system, which offers a user-selectable range. “A frequency-agile system is always preferable to a fixed-frequency system,” says Seattle-based Nick Kolias, who does production sound for news, broadcast, commercials, documentaries, and corporate projects. “In this world of RF overload, it's a lifesaver having a system that can be retuned away from trouble. Just because a frequency is clean one minute doesn't mean it will stay that way for the day or even the next hour.”
Once you've got a clear frequency, you may have to take steps to keep it clear if there are many other users in the vicinity of the shoot. “When I get into a situation where a lot of people will be showing up with a lot of unknown freqs, I will burn batteries in my transmitters from the time I arrive,” says Bob Charlap, a Dallas sound man with 18 years of experience for clients such as Fox Sports, ABC News, and CBS Sports. “This will prevent the latecomers from firing up on your freqs, providing they scan for used freqs when they arrive. It may cost a little more in batteries, but it keeps people away from your planned frequencies for that event.”
Product placement
When working with wireless body-pack transmitters, the position and placement of the antenna can greatly affect the performance of the system. Kolias says it's typical to clip the transmitter on a belt at the back of the talent or to slip it in a pants pocket. “This is convenient and easy to do, but it won't always give you a good RF signal. The problem is that the human body is basically a large saline sack that is very efficient at absorbing radio waves. When the line-of-sight path between the transmitter and receiver is blocked by a body, it can cause significant RF loss. Clothing can make the problem worse if it pushes the antenna toward skin and thus increases RF absorption.”
Clothing can also affect the rubbing noises picked up by the mic. “The cable is very sensitive to rubbing noise,” Boyll says. “Instead of running my mic cable to the body-pack transmitter sideways around the waist, I try to keep it away from the shirt-front and tie, which are very prone to noise. Instead, I run it up the talent's back and over the shoulder. But be sure to create some strain-relief by taping at several points along the path of the cable on the inside of the shirt or jacket.”
The first rule of choosing a location for a receiver is to minimize the distance from the transmitter. “Make long cable runs — taped down for safety — do the work that wireless cannot,” Boyll says. “Then put the receiver as close to the edge of frame as possible.”
Beyond simple distance, another consideration is whether the transmitter is surrounded by obstacles. “You can minimize interference by having an unobstructed path between the transmitter and receiver,” Johnson says, referring to “metal, bodies, steel or concrete pillars, anything that could cause interference. It's a good idea to get as near to the person or people wearing the transmitter and still be out of the shot.” Johnson says that on some shoots he's even had a PA walk holding the receivers in order to maintain a clear path.
Gain throughout the chain
Sending a microphone signal through the additional stages of wireless transmission means there are more opportunities for variance in the gain structure, so you have to be extra careful to optimize levels throughout the signal path. According to Kolias, that starts with setting the microphone input level adjustment on the transmitter correctly. “If that's not done properly, it can have a major effect on the quality of sound no matter what the cost of the wireless system.” He also suggests using high-output microphones. “This allows the transmitter gain to be set lower,” he says, “and usually results in a much better signal/noise ratio that can easily be heard.”
Kolias also says that high-power transmitters, which are available from several manufactures, can make a real-world difference in the performance of wireless systems in certain applications. Similarly, he adds, high-gain receiver antennas are “great for pulling in weak signals or greatly increasing the reliability of a wireless link at a short distance.”
Whatever system you use, the likelihood of problems is further reduced if the equipment is tweaked for peak performance. If you own your own, Boyll recommends having the transmitting and receiving units professionally “tuned up” once a year.
Don't skimp on batteries
In certain situations it can be inconvenient or even impossible to change a wireless transmitter battery without causing a major disruption.
“On an all-day project, changing batteries can become a dreaded and stressful event, especially with multiple wireless systems,” says Kolias.
“That's when lithium batteries are the only way to go. All things being equal, a lithium battery — 9V or AA — will usually last at least three times as long as an alkaline battery. The only downside to lithium batteries is the cost: they range from four to five times more expensive than alkaline counterparts. While it may not be cost-effective to use lithium batteries exclusively, they can be a vital tool.”
Back it up
Even when you've done everything right, there may be times when circumstances conspire to make wireless unworkable. “Offhand, my biggest tip with wireless would be: back yourself up,” says Tracy Forrestal of Los Angeles, who speaks from 17 years of network experience covering politics, disasters, entertainment, features, and travel. “Much of what I do — red-carpet arrivals at premieres, parties, award shows, etc. — allows only one take, so you can't afford dropouts, interference, or hits on your wireless. Use a hard line, too, or have one standing by, or use a second wireless, or your boom. With wireless, you lose a bit of control, so backup becomes that much more important.”
Philip De Lancie is a freelance writer covering media production and delivery technologies in areas including DVD, professional audio, multimedia, sound for picture, and the Web. He can de contacted at delphi@mindspring.com.
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