In recent years, performing musicians have enjoyed many technological innovations that have made their lives easier. Manufacturers from all corners of the industry have developed products, from modeling amps to powered subwoofers to automatic feedback eliminators, that make gigging more manageable.
Perhaps the most encouraging long-term trend in the live-music arena is the steady development of wireless technology. Wireless systems continue to become cheaper, smaller, better, and more reliable. Whereas wireless was once a luxury item, viable for use only with the highest of the high end, today's systems have made it possible for budget-conscious working musicians to join the party, too. The increased mobility you gain by shedding the cables attached to your instruments or mics can profoundly affect your whole approach to live performance.
Although wireless systems still have their problems, advantages far outweigh disadvantages. The joys of being liberated from your cables will make you wonder how you ever put up with them, and why everything can't be wireless — even with the accompanying caveats.
HOW WIRELESS WORKS
Despite the magic of transferring your licks through the air, operating a wireless system is straightforward, old-news stuff, at least from a technological standpoint. A wireless system is just a miniature FM radio setup. Sound from a microphone or pickup is converted into radio waves by a transmitter and sent through the air with an antenna. Most systems are based on analog technology, although Sennheiser is pioneering a digital wireless approach (notably in their Digital 1000 series), in which the signal is encoded into a 20-bit data stream that is decoded on the other end.
The transmitter, connected to the mic or pickup by a short wire (and sometimes sporting an external antenna), is small enough to fit inside a handheld mic shank or a box the size of a cigarette pack that fits on a belt or straps to the small of the back. The airborne radio waves are then picked up on the other end by a receiver (a larger box, usually a single-space half-rack or full-width unit), also outfitted with an antenna, which converts them back into an audio signal. That signal then goes out of the receiver through a ¼-inch or XLR cable and into your sound system — mixer, amplifier, effects pedalboard, and so forth — exactly the same way it does with conventional wired gear. That means you can freely mix wired and wireless sources within a mixer, and your soundperson doesn't have to make any special concessions.
GO CONFIGURE
It's easiest to understand the operation of a wireless system by first considering the available physical configurations for musicians. Fig. 1 is a flowchart of the most popular musician-based wireless hardware systems. Keep in mind that these configurations represent just the standard, established setups.
Naturally, exceptions and variations to the six basic configurations occur. For example, Samson Technologies' AirLine system and AKG's WP series do away with the whole belt-pack system by putting the transmitter and antenna all in the same rig as the mic. Also, you can buy special capsules with a built-in transmitter and antenna that feature a standard three-hole XLR jack. These capsules allow you to plug right in to the bottom of your existing wired mic (like your trusty war-weary Shure SM58), transforming it into a wireless. But when a wireless system includes a mic along with its transmitter and receiver, it's best to consider the package as a whole.
Whether you're running a single setup for your particular electric guitar or considering a whole fleet of mics for your gospel choir, all wireless systems share common controls and features. Let's take a look at these elements first, because they're what you'll use to compare systems.
TRANSMITTERS
The transmitter is the first step in the wireless chain after the input device. It takes the audio signal from the input, compresses it by a 2:1 ratio, and modulates it with a radio frequency (RF) signal (digital systems do not need to compress the signal). The RF signal radiates from the antenna, propagating through the air in all directions, where, hopefully, it will meet up with a nearby receiver. Below are some of its chief controls.
Battery power
Because it is portable, the transmitter typically runs on 9-volt or AA battery power (whereas the receiver, a stationary object, runs on plug-in AC power). So a transmitter features a battery compartment, which you will access many times in your wireless career. Because reliable battery power can be generated only with an alkaline battery (never rechargeables) at or near full strength, it's best not to use any one battery continuously for more than ten hours. For a critical gig or if you're compulsive about your sound, you might change it more often than that.
Antenna
All wireless transmitters must have an antenna through which to propagate their signal. With a handheld mic, the antenna is either encased in the mic housing, rendering it invisible, or it protrudes from the base as a piece of stiff or flexible wire. In a belt-pack system, the antenna is either included in the audio cable that connects the mic or instrument plug or it dangles from the bottom of the unit, and it is typically a flexible piece of coated, coiled wire (called a whip or a rubber ducky) a few inches in length.
On/off switch
This control is fairly cut-and-dry. You turn off the power when you're not using the transmitter for long periods of time, which helps preserve battery life. But you should consider when it's appropriate to cut the power and when you should cut the audio (which you do with the mute switch, explained later). Cutting the power eliminates the “frequency lock” that your transmitter and receiver have established, requiring a little time for them to find each other when you power back up. Turning off the transmitter also allows spurious (foreign and unwelcome) signals to come through the receiver and into the sound system on that frequency.
Mute
A mute switch should be used when you want to stop transmission momentarily or for short periods of time. A mute switch is designed to make graceful audio transitions between mute-on and mute-off (without pops or hisses during operation) and should be used much more than the on/off switch.
Gain control
The gain control in a wireless system is similar to a preamp's gain control. It dictates the strength of the audio signal coming out of the transmitter and works in conjunction with the receiver's level control to determine the overall level of the signal going into the sound system.
RECEIVERS
Receivers are the end of the line as far as the wireless process is concerned. They snatch the modulated RF signal from the air, demodulate it (converting the RF signal back into audio), expand it back to its original dynamic range (by a 1:2 ratio), and then electrically prepare it for your sound system. Systems will vary in the number and implementation of features, but the following are some of the most important ones.
Antennas
Sticking up like a couple of cockeyed rabbit ears and distinguishing the receiver from other signal processors in the sound booth are the antennas. Most wireless systems feature two stiff-metal telescoping antennas that each receive a signal, the better of which gets put through the system. (This is known as diversity, which I will discuss in detail in a moment). Antennas are on swivelmounts, so that you position them for best reception (contrary to popular belief, you should not “aim” the point of the receiver's antenna at the transmitter). Reception is ideal when an open-air, line-of-sight path can be established between transmitter and receiver and the antennas can be splayed at a 45-degree angle. Some receivers offer the option of front mounting the antennas as well as top mounting them, allowing you to rackmount your receivers.
Gain control
Working in conjunction with the transmitter's gain control, the receiver's gain control determines the strength of the audio signal going into the mixing board, amp, or other signal processor. The standard gain-stage practices apply here: set the gain high enough that the signal is substantially above the noise floor, but not so hot that it distorts when a high-level source signal appears at the input.
DISTINGUISHING FEATURES
Now that you've had the tour of the controls, let's dig a little deeper and see what's going on inside the box. Here are some of the most important features to consider when choosing a wireless system.
VHF and UHF
These acronyms are short for very high frequency and ultra high frequency and refer to standardized bands (or ranges) of radio frequencies. The VHF range — which also applies to some radio-controlled toys, cordless phones, and walkie-talkies — starts at 49 MHz and extends through 108 MHz, the last numbers on the tuner display on your FM radio (see Fig. 2), and tops out at the usable limit of 216 MHz. The lower-numbered TV channels exist within that range. The advantage to using VHF is that because of their long wavelengths, VHF frequencies travel very well through the air and other nonmetallic materials. Systems designed using VHF frequencies use less battery power and are less expensive than UHF systems.
The downside to VHF is that it's more prone to interference because of all the activity in the limited number of frequencies in that band. UHF has much shorter wavelengths, and so the potential for reflection off of metal and other surfaces is greater, resulting in a potentially shorter range, given the same power. But the shorter range can work to your advantage, because it means that you're less likely to encounter interference from other wireless systems in the vicinity. In addition, because the standards allow for greater occupied bandwidth and deviation in the UHF range, the signal benefits from greater dynamic range and frequency response — both desirable qualities for musical signals. (Digital receivers, because they are looking for a unique code in a digital data stream, reject RF signals from the VHF and UHF bands — which ensures against interference — and get their dynamic range from the 20-bit encoding, not from deviation.) The highest-quality systems are UHF based, but that doesn't mean VHF won't do the job.
Diversity
Diversity is a reception technique in which two antennas are used to eliminate dropouts that occur when multiple paths arrive at the receiver at different times and cause phase cancellation (see Fig. 3). A dropout can either be a “noise up,” which means the audio path remains open but the signal is weak and noise floor rises, resulting in hiss or, if the phase cancellation is deep enough, a pop as the squelch circuitry kicks in and out.
An antenna diversity system constantly monitors the antennas to see which is providing the stronger signal at any given moment. The receiver then takes the strongest signal. A True Diversity system goes one step further and uses two separate receivers housed in a single unit. Whichever receiver produces the strongest signal is the one that is used. Recent developments in diversity technology provide a number of methods for selecting the best signal (not necessarily the strongest) by using different schemes, ranging from antenna selection to dual receivers.
Frequency tuning and channel selection
Two wireless systems in the same area cannot have the same operating frequency, so any time you have more than one wireless mic in a setup, you must know what the operating frequencies are and how to change them so that each mic can have its own unique frequency. Shared by a transmitter and receiver, a channel is a discrete location for a unique frequency that includes its deviation range (the amount the signal is allowed to vary according to the changing input). Not only must each musician have his or her own transmitter and receiver, but each one must also be operating on a separate channel.
Also, you're competing for operating frequencies with more than just other wireless systems in the same room (or down the street at the local karaoke bar — remember, radio waves travel through glass and walls as well as air). Many times local TV stations cause a conflict. (When manufacturers ship wireless systems to music stores in different regions, they pretune them to noncompeting TV station frequencies, so at least you don't have a conflict right out of the box.) Your wireless transmitter is limited by government regulation to a given signal strength that will transmit as far away as 1,000 feet. But TV station broadcasts are much stronger, obviously, and so will crowd out, or at least severely interfere with, your attempts to reach your receiver. That problem is especially acute in outdoor situations where there are no barriers to block airwaves other than your own. A multicity tour of outdoor venues would be just about the most problematic scenario for a wireless system.
However, if you're diligent and you do the research, you can get a list of all the operating frequencies of the local TV stations in the cities you're visiting. You can then figure out how to tune your wireless systems so that there will be no conflicts. Manufacturers of wireless systems understand the importance of helping their customers in this regard, so many of them post helpful frequency charts on their Web sites. The Web is the perfect medium for this information, as new stations are always coming into existence and will continue to do so as the digital television market grows. Other systems operating in the same frequency range include land mobile radios, which include CB, the band used by truckers and taxi cabs. Any motor, engine, or electromechanical device that emits a powerful electronic field can also interfere with your system by producing spurious transmissions.
WHO SHOULD GO WIRELESS?
Whether you decide to introduce a wireless system into your music-making activities is entirely a personal choice. But if you're considering taking the plunge, it's a good idea to know beforehand what's involved in setting up and using such a system. What some people might consider to be an unnecessary hassle, others would view as preparation that's well worth the benefit. And wireless miking makes more sense for certain categories of musicians than others, even though virtually any player can identify some benefit from dispensing with all that cabling. Here are some of the most likely candidates for going wireless.
Vocalists
If you're a vocalist who's considering the wireless route, you may wonder whether you should go with a handheld or a headset. If you don't do a lot of wild choreography, you have a free hand (meaning you're not playing the guitar or another instrument), and you're restricting your travels to the stage, go with a handheld. Because of their larger physical size, they tend to offer better sound quality. They also look more like a standard mic, which probably means you can easily transfer your mic technique to the wireless version. For example, you may be used to using the proximity effect (the phenomenon where the bass response increases dramatically as you get closer to the mic) to your advantage.
On a headset mic, you can't really vary your position relative to the mic with the kind of freedom that you can with a handheld. A handheld allows you to move in and out and bob and weave as your voice alternates from booming thunder to tender whisper. Also, you can still place a handheld in a mic stand and use both hands for dramatic stage gestures (reaching both free hands out in supplication as you sing, “Oh, baby, don't leave me, I'm begging you”), or for when you strap on your guitar.
The newfound mobility that wireless affords vocalists can be fun, but it has its disadvantages. One obvious drawback is that the farther the singer is from the stage, the longer it takes the backing music to reach him, and so a confusing time-delay effect can set in between the lead vocal and the instruments. (This can be rectified with wireless in-ear monitors.) Also, if you're used to taking vocal cues from the singer, and it's a really big venue, you can actually lose sight of the wireless performer (though you can hear him or her just fine). That can result in missed cues, if the singer is used to signaling, for example, “Last time and then the tag,” or “Help, I'm being kidnapped and taken out to the parking lot by crazed fans.”
Going wireless has the most appeal for vocalists because they're generally the most mobile of the onstage performers (though Pete Townshend and Eddie Van Halen might disagree) and, as front people, have the best excuse for getting out to the audience. But other groups of musicians are joining their ranks, too, and for better reasons than just mingling with the masses.
Guitarists, bassists, and keyboardists
These days, guitarists and bassists are just as visible as lead singers, and so it's natural for them to want the aesthetic freedom that vocalists enjoy when going wireless. And with a strap-on keyboard, keyboardists can not only move front and center, they can crowd-surf the house, just like Eddie Vedder.
Playing wireless guitars, basses, and keyboards allows you not only to travel, but to spin in place without winding up cocooned in your own cables (good for circular stages). In addition, you can do-si-do around other more stationary musicians onstage without fear of entanglement. Here's a tip: if you're a guitarist or bassist who is considering buying a wireless system, listen to its compansion performance. (Compansion is a process that involves compression of a signal before transmission and expansion after it's received.) Compansion can sometimes have adverse effects on your tone. Inferior schemes can cause companding artifacts, which are especially noticeable in bass guitar signals as the audio trails off.
Horns, strings, and other band instruments
For horns and strings, wireless miking offers the prospect of not only increased stage mobility but freer movement all around. Horn players like to bob and weave, too, and when you have your whole body into the groove, unburdened by a cable, you can't help but play more expressively. If your horn section is entirely wireless, there's no reason why you can't give them a choreography routine to rival that of Gladys Knight's Pips. Going wireless for section members means it's easier for an individual to step out front quickly for a solo or featured passage and duck back upstage to rejoin the section, without fear of getting tangled.
Horn and string players who appreciate the increased freedom can adapt a lavalier mic or opt for a clip-on mic specially built for acoustic instruments. Such mics are typically larger than lavs, for which part of the aesthetic is to hide the microphone itself. With acoustic-instrument clip-on mics, the element's presence doesn't have to be so surreptitious, so it can be constructed with larger diaphragms and attendant housings. In addition, microphones designed for instruments instead of voices are better built for high sound pressure level (SPL), something lavaliers don't generally encounter.
LOW END OR HIGH END?
Like any other technology, wireless systems include a range of solutions that vary in quality and features. Because the technology is imperfect (subject to dropouts, distortion, and interference), the wireless system you buy should be the best your budget will allow. It's an integral part of your signal chain, after all, and when the wireless goes on the fritz, it's just as bad a broken string, a shorted audio cable, or a blown speaker.
However, you can get away with an inexpensive VHF system if you meet one or both of the following criteria: (1) you don't mind lowering your expectations in exchange for the savings or (2) you intend to place limited demands on the system, such as working in a well-insulated room (a basement club) with a short transmission range.
But if you plan to outfit a band, travel and play outside, and perform in large venues, you'll need to get a UHF system with true diversity and multichannel selectability. You'll need to be aware of which TV stations broadcast on what frequencies so that you can tune your units to avoid conflicts. A TV station is much more powerful than your Chiclet box of a transmitter and will still have sufficient juice to find your receiver and wreak havoc with your sound, even when you're ensconced in the back room of the aptly named Dungeon Dance Club.
You can easily prepare for any venue, however, by doing a little advance research on the Web, and you can also troubleshoot problems that spring up if you're fearless in the face of opening the transmitters and tweaking the receivers.
UP IN THE AIR
If you have a genuine curiosity about the activity going on in the airwaves around you, you'll have no problem handling a wireless. Manufacturers offer extensive charts and tables that help in this regard, and you can get the hang of tweaking your system in no time. After a while, it's just like tuning: it's another task, maybe, but not one that creates a lot of anxiety.
After you acclimate to a wireless system, you'll find you move more freely and that you don't have to check your impulses — at least the ones that inspire you to jump, strut, crowd-surf, or just dance around like an unbound fool. When you're onstage and you can do several 360s without worrying that you're going to wind up like a spool of thread, or when you can jump off the riser and into the crowd without getting yoked back by your mic cable, you'll feel as though you have slipped the surly bonds of the earth, if only for a moment. And if you ever feel the need to stage-dive while simultaneously playing your guitar, it's nice to know that with a wireless system, you can.
GLOSSARY OF WIRELESS TERMS
Adjacent channel rejection
The ability of a radio receiver to reject interference from an undesired signal on another nearby or adjacent channel.
Antenna
On a transmitter, the device that radiates the radio waves through space; on a receiver, the device that receives radio waves.
Carrier
The RF signal that contains the audio information.
Channel
The specific frequency used by a transmitter and receiver and the associated bandwidth necessary for the transmission (typically plus or minus two times the deviation).
Companding or compansion
The process of compressing a signal before transmission and expanding it after reception to help increase dynamic range and eliminate interference. Wireless systems compand at 2:1 and 1:2.
Crystal
A small quartz crystal that serves as a stabilizer for the designated operating frequencies of the transmitter and receiver.
Demodulation
Decoding the modulated RF signal introduced by the system's transmitter.
Diversity
The ability to avoid weak and phase-cancelled signals by selecting the strongest signal at a given moment from any active antenna.
Dropout
A momentary loss of audio signal that results in no sound, or noisy sound characterized by hisses and pops.
Helical antenna
A flexible, plastic-coated, coiled-wire antenna. Also known as a rubber ducky.
Interference
Any unwanted signal or frequency introduced into the system that produces undesirable results at the output.
Intermodulation
The mixing of signals in a wireless system that creates new, undesirable frequencies at the output.
Limiter
Circuitry that limits the amount of modulation in accordance with government regulations.
Modulator
Circuitry that superimposes an audio signal on an RF signal by varying its frequency in synchronization with the audio signal.
Multipath or multipath null
RF signals that arrive at a receiver at different times because of different direct and reflected transmission paths. These signals are out of phase, resulting in signal loss. If the signals are of opposite phase, they will cancel completely, creating a multipath null.
Mute
The control that silences the audio signal in a transmitter.
Propagation
The process of a signal radiating through a medium, such as air.
RF
Radio Frequency. In wireless technology, any signal above approximately 1 kHz (0.001 MHz).
RFI
Radio Frequency Interference.
Selectivity
A receiver's ability to reject signals near its operating frequency.
Squelch
Circuitry that mutes the output when it detects that the audio has dipped below the user-established threshold. In smart squelch systems, the output is muted when the system detects unwanted signals regardless of level.
True diversity
A type of diversity that uses two separate antennas and two separate receiver channels tuned to the same frequency. Also known as dual diversity and space diversity.
UHF
The frequency spectrum in the range of about 300 MHz to 900 MHz.
VHF
The frequency spectrum in the range of about 50 MHz to 300 MHz.
Wavelength
The distance a wave travels in time in one complete cycle.
Whip
A flexible or stiff antenna that dangles or protrudes from a receiver.
