Despite the wondrous range of new gizmos and gadgets currently available to bend, shape, twist and color sound signals, there is still nothing that can substitute for the right microphone in the right position for the job at hand. The variables among microphone characteristics are substantial, however, general guidelines provide a solid start to any task using microphones for the more frequent television production formats.
Dynamic and condenser mics
It's important to choose the proper mic type and polar pattern. Dynamic microphones work on electromagnetic induction and are comparatively simple in design. For TV production purposes, their primary advantages are that they are tough (you can actually drive nails with some of them, though it won't help the cosmetics), and they don't require phantom power to operate. That's generally why these end up in ENG vans and road kits.
The dynamics share this space with electret condenser microphones, which require either an internal battery or phantom power from a mixer to operate a tiny preamplifier inside the microphone case. They generally provide better frequency response and higher output than dynamics.
The manufacturers of some field recorders recommend using condenser mics to provide a better signal-to-noise ratio from the recorders' microphone preamps. Condenser mic design has come a long way, but for pickup of loud sound sources like musical instrument amplifiers, a dynamic mic is less likely to produce SPL overload and distortion because it doesn't have an internal preamplifier.
However, many of the newer condenser microphones have a switch on the case that can attenuate the signal by 10dB or 20dB for loud source pickup. Wireless mic body pack transmitters have a similar attenuation switch inside the case, and this is typically used when the transmitter is empolyed with an electric guitar or similar instrument with a higher output than the microphone.
Pattern and frequency
The second basic consideration is the pattern. Any new microphone should come with a polar pattern printout showing the directionality at various frequencies and the effect of pattern-changing switches. This should always be accompanied by a frequency response graph.
Due to basic audio frequency physics, microphones are less directional as the frequency goes toward bass. Low-frequency sounds penetrate, while higher audio frequencies bounce off solid objects like walls. Did you ever notice that you can hear the bass and kick drum from a live band while standing in the parking lot, but when you walk in the dance hall door, suddenly there are drum cymbals? In real-world use, microphones represent a typical case in which you don't get something for nothing. There is always a trade-off, and this is the essence of experience in microphone selection.
Omnidirectional microphones are less sensitive to breath popping and sound coloration when used for close-up handheld vocal applications, such as a reporter doing a standup in a high-noise environment.
Cardioid microphones pick up less background ambient sound, but require thicker (and more obtrusive) pop filters. Also, they tend to have a proximity effect that emphasizes bass when held close to the mouth. Singers often use this effect to their advantage.
Shotgun or hypercardioid microphones provide a tighter pattern but emphasize the proximity effect. For this reason, these types are used in situations where the microphone can't be placed close to the sound source.
Hypercardioid podium microphones can help prevent PA system howling by providing more gain before feedback, and this is a typical case in which the correct microphone choice should come before twisting any EQ knobs on the mixer. One hallmark of inexperienced sound operators is that they tend to think that EQ knobs only turn to the right.
Levels and power
Microphone lines carry weak, tiny signals that are vulnerable to inductive noise and hum from motors, lighting dimmer packs and ground loops. Balanced lines help reject induced noise. However, the best defense against background AC hum and other sound system trash is to kick up the signal level at the earliest possible point with a preamp.
A good battery-operated preamp can sometimes be placed inside a podium and supply the phantom power necessary for condenser mics. Most include a limiter, and gain can be adjusted, usually in 5db to 10dB steps. Many of the newer digital snakes also have preamps built into the snake head, and these may be remotely operated. Any time a mic signal is being split for separate house, broadcast or stage monitor feeds, the splitter should include a direct path for mixer-supplied phantom power and a transformer isolated path with a switchable ground lifter. Every sound kit needs to have one because it can also be used to isolate powered speakers and other sound gear that may get its power from an AC source incompatible with that running the main mixer. Phantom power levels typically run from 12V to 48V, and the higher the original sound levels, the higher the voltage on the phantom power that may need to be used. Podium microphones for normal speech can usually get by on 12V phantom power.
Among the more frequently used techniques of mic placement for stereo recording is the coincident pair using two cardioid pattern microphones angled at about 90 degrees with the capsules placed as closely together as possible without touching. This works particularly well for recording sources that are spread out over a wide area, such as symphony orchestras, studio audiences and crowds at sports events. (See Figure 1.)
The coincident pair best guarantees monaural compatibility, while a spaced pair enhances the spatial effect of channel separation. In the case of the orchestra, the mics are typically hung about 20ft above and behind the head of the conductor. A number of coincident pairs may be needed on tall stands to capture the stadium or gymnasium crowd at a football or basketball game.
It is important not to put the signal from the ambient mics through the same compressor that is used for the announcer or sideline reporter microphones. Instead, group the mic signals for compression, because the variations in their close-mic levels will cause the compressor to pump the crowd sound, and this can be distracting to listeners. (See Figure 2.)
Parabolic mics used on football games can also have a noticeable effect on the crowd ambience because they are normally heavy on upper middle frequencies due to the size of the parabolic bowl. Parabolic mic faders should be treated like an airplane throttle — smoothly up and smoothly down.
Panel talk with lapel mics
The electret condenser lapel mics used on talk shows can be either omnidirectional or cardoid, but once again there is a trade-off. With half a dozen guests on the set, cardioids sound less reverberant but usually require pop filters.
Omni lapel mics don't pop as easily, but tend to pick up the other guests nearby. In a free-form discussion format, noise gates are no panacea because they can be triggered by guests on either side of the one talking, depending on which way the speaker's head is turned.
The best results are reached by anticipating the flow of conversation and keeping each guest's mic slightly below normal operating level until they begin to respond to the host. Multitrack recording can clean it up perfectly. However, in most production situations, the time required for post mixing is a luxury and, of course, not an option on live shows.
Once the characteristics of the microphones are familiar, audio for TV production formats isn't especially difficult to learn, but there's no substitute for on-the-job experience.
Bennett Liles is a writer and TV production engineer in the Atlanta area.