Choosing the Right Radio Mic", by Larry Loewinger
"I've just passed the parking lot," my friend advised me. He was a block and a half from my apartment, walking on the streets of New York City on a cold, blustery day and talking into four wireless microphone transmitters, as tourists' heads turned from their guidebooks to watch my muttering friend. Back in the comfort of my apartment, I cruised through the dials of the mixer to which each radio mic receiver was connected. The point of this exercise was to test the mics for range and audio quality. Two were struggling-one almost dead, the other wheezing and coughing the way radio mics do. The other two were displaying reasonably good manners with only occasional drop outs. One, in fact, exhibited a surprisingly stable signal. What was significant was not the fact that these mics were struggling, but, even at their worst, that they were working at all in the intense radio-frequency environment that is New York City.
The radio microphone systems we were evaluating, all in the $1,000 list price range and all intended for the digital video market, reflect the advances that radio frequency technology has made in the last 10 years. By operating in the Ultra High Frequency (UHF) range (470-806 Megaherz), these devices were far more resistant to interference than the older Very High Frequency (VHF) units (150-216 Megaherz) they have replaced. Their radio frequency (rf) coverage has increased, too. Bear in mind that we are still only talking about a reach of some 300 feet in circumference, but within which reach the rf signal is far more stable. Wireless microphone technology has evolved to the point that, in a sense, we have gone back to basics. The emphasis is no longer on merely securing the rf signal through the use of expensive high-gain antennas, but rather on getting good sound-maximizing the sound quality of the lavalier microphone.
A wireless microphone system is a highly miniaturized FM radio station. The subject wears the transmitter which radiates between 50 and 100 milliwatts of rf power several hundred feet out to the receiver, which is somewhere near the sound mixer. Production radio microphones operate in the same bands as do television stations, both VHF (Channels 2-13) and UHF (Channels 14-80), only in between the TV channels. With the advent of digital television, the allotted bandwidth for wireless microphones is steadily shrinking. If you're buying a used rf mic, be careful not to choose one whose frequency has since been given over to digital TV.
Production people believe radio mics save time. That's true, although it is sometimes at the cost of quality. Wireless mics have other advantages as well. They convey dialogue from someone deep in the frame who otherwise couldn't be recorded. They can enhance dialogue that is softly spoken. They can retrieve dialogue in a noisy situation, such as on city streets. In a documentary environment, radio mics allow you to 'steal' dialogue when a speaker close to the subject is unaware of being recorded. Sometimes even the subjects forget they are wearing them.
But there are drawbacks as well. With radio mics one loses a sense of perspective or placement of an actor or documentary subject within the film or video frame; the sound is always up front. Clothing noise is a constant headache, especially when multiple rf mics are involved. As good as radio mics have become, rf interference can still be a problem. And radio mics, as they invade the privacy of the people wearing them, require an interaction (sometimes unwanted) between the sound mixer and his or her actors or subject. There are actors who hate them and will sabotage your efforts to use them. Nonetheless, hardly a film, TV show, or musical stage performance can proceed without them.
What should you look for when buying a radio microphone? Professional sound mixers today expect that their radio mics will be as miniaturized as possible; they expect a balanced XLR audio output, detachable antennas that attach firmly and securely to the units, a transmitter with a reasonably standard microphone input connector, mechanical ruggedness, ease of operation, comprehensive metering, a high-quality diversity switching system (more on this below), frequency switching (agility), and a secure operating range of about 300 feet in circumference. Most of all, the rf microphone should sound good. All these requirements come at a price, and the cost of professional wireless microphones can be steep. A frequency agile, diversity system begins at about $2,300, and can approach $5,000 at the very top end. If you're a filmmaker or videographer planning to spend less than $1,000 on a wireless microphone, what compromises can you expect and can you live with them?
Due to the rapid strides in rf technology, wireless manufacturers have been able to pack a lot of quality into their low-end units. Menus rather than switches have shrunk components and brought down their price, as have unbalanced mini-plug audio outputs and receiver and/or transmitter antennas that remain permanently attached to the units. Only one of the systems that we examined works on a diversity switching principle. Diversity switching (usually shortened to "diversity") involves a method of reducing multi-path dropouts by utilizing two antennas or receivers that seamlessly switch back and forth to eliminate out of phase rf signals. While diversity switching may increase the reliable reach of a radio mic, the primary gain is in an increase in rf reliability within the system's operating range. Because diversity technology is so reliable, it has meant the beginning of the end of cables on a sound cart. There are professional mixers I know who do all of their recording via wireless boom mics, lavalier wireless mics, and wireless headsets. In the digital video world, more producers, directors, and camera people want to link up the sound person and his or her audio mixer via a radio link to the DV camera. That connection is best served by a diversity rf microphone. But there is a cost to diversity, usually in money spent, the extra size of the receiver, and its power consumption.
There are six manufacturers who dominate the digital video radio microphone market: AKG, the Austrian microphone manufacturer; Audio-Technica, a Japanese maker of consumer and prosumer products; Lectrosonic, the leading American maker of rf technology; Sennheiser, Germany's largest producer of microphones and headsets; Sony, whom we all know; and Telex, an American company best known for its communication systems. I have investigated the four most popular brands-Audio-Technica, Lectrosonics, Sennheiser, and Sony-to see how each responded to the DV market. While we did no formal rf measurements and no test instruments were involved, we subjected the mics to several rigorous but informal tests that you as a consumer can do. We placed the mics on someone just as they would be used in the field and had that person walk the streets of New York to see how they performed. We jangled keys close to the lavaliers, and we shouted into them as a way of measuring the quality of their compandors and limiters. Jangling keys produce an enormous amount of high frequency energy that can severely tax the compandor circuitry of a radio mic. Reproducing this sound without distortion is a major challenge to an rf mic. And shouting into the lavalier is a measure of how these systems' limiters protect them from audio overload which can overload the transmission system as well.
All four systems we looked at were frequency agile. In two cases the frequency alterations were made by mechanical switches, and in the other two they were accomplished by a digital display and software. All systems were supplied with lavalier microphones of varying quality.
Only one of the mic systems comes with a balanced audio output delivered via an XLR connector: the Audio Technica U100 series, which is also the only diversity receiver among the group. Its rf and audio parameters are changed by means of mechanical switches, and it requires two batteries to operate the receiver, the only one to do so. Since it is not as ergonomically pleasing as some of the other units, the question we had was whether its performance would override its appearance and the large size of its receiver. The answer is yes. The Audio Technica's rf reach was the longest, if not by much. Its audio quality is exemplary, as was that for all the systems we examined. The Audio Technica U100 wireless mic is a good buy if you don't need a small receiver to attach to your DV camera.
The smallest system and probably the most ergonomic is Sony's WRR-805A receiver and its companion transmitter, the WRT-805A. It is the only system to use AA batteries and be encased in hard plastic rather than metal, making it the lightest of all four mics. Sony also supplies a very clever and flexible receiver harness that should make it easy to attach to various DV cameras. While Sony provides a multilingual operating manual, it also prints the basic operating instructions on its transmitter and receiver-a very handy thing. (Lectrosonic does the same.) Generally speaking, radio mics are very easy to operate. Rare is the situation where you need more than the kind of elemental advice offered on the shells of the Sony and Lectrosonic systems. Sony's functions were altered by a blend of hard switches and software. As you might expect from a manufacturer of DV cameras, Sony has produced a system that is attractive in all parameters save one-the strength of its rf signal. Its rf operating range was the weakest of all four units. While this is a serious weakness, it is not a fatal flaw as long as you don't push the rf envelope.
Lectrosonic may be the most accomplished American manufacturer of wireless microphones. Their entry into the DV market is the 100 Series transmitter and receiver. As a non-diversity system it had excellent rf range, approaching Audio Technica's diversity system. The transmitter physically resembles Lectrosonic's high-end transmitters. The microphone input features a Switchcraft connector, the same as is found on Audio Technica's wireless mic. Wouldn't it be nice if all manufacturers standardized to this connector? All switching in the Lectrosonic system is done mechanically. Its receiver is small, with one drawback-a permanently attached antenna-and its output appears on an unbalanced female mini plug. Clearly this receiver is intended as a camera-mount unit. The Lectrosonic system is the most expensive of this particular group.
In Germany, Sennheiser is a major manufacturer of both consumer and professional audio products. It exports high-quality regular microphones, headsets, and high-end radio microphones which are found mostly in the theater world. The Evolution series, which is their entry into the DV market, is a solid example of current technology. Like the Sony unit, it makes its frequency changes through software. Both of its antennas detach from their respective cases. It is mechanically rugged and performed in the field with good rf range, trailing the Lectrosonic and Audio Technica microphones by only a small amount. However, when it came to audio results, the Evolution 500 performed less well. Keys distorted badly when jangled too close to the lavalier. If you listened closely, the system's compandor seemed to have some difficulty in reproducing low-level sound information. Background noise appeared gritty. In most situations, when the transmitter's mic input gain is set carefully, this problem won't be apparent. Given that Sennheiser is the leading manufacturer of regular microphones-its Evolution 500 is available with one of the better lavaliers on the market-the Sennheiser MKE2-EW, for which you will pay a premium. While the Sennheiser mic has its virtues-namely its rugged build and its good rf reliability-it clearly has some notable drawbacks.
Which to choose? If your requirement is for a camera mount system, your choices are either the Sony or the Lectrosonic, which have better rf reach but greater cost. If you want the superior reliability of diversity technology, then your only selection is the Audio Technica U100. The Sennheiser Evolution at this price range is a middle of the road choice that does many things well, but no design element stands out.
To most of us, radio frequency technology is one of life's little mysteries. Few of us understand it, but we happily take it for granted every time we turn on the radio. When you go into the broadcasting business, which you inevitably do when you buy a radio mic, ignorance is no longer bliss. One item to help you comprehend this mystery is a substantial booklet published by Lectrosonics, Wireless Microphone Systems: Concepts of Operation and Design. While this may include far more information than you want to absorb and it may promote Lectrosonic products (though not too heavily), it is very useful as a reference. What's more, even though it lists for $15.95, it is free from the Lectrosonic website (www.lectrosonics.com, click on Wireless guide). And that's a blessing when the switch to digital technology keeps filmmakers digging into their pockets.
Larry Loewinger is an audio engineer and documentary producer.