Radio Broadcasting, Technology of

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Any discussion of the technology of radio broadcasting must, at the outset, acknowledge its rapidly changing nature. The almost exponentially increasing effect of computers is being felt in the domain of radio as it is in most other areas. Although computers have not replaced all of the tools in use in radio broadcasting by any means, they have greatly enhanced the effectiveness of most, if not all, of them.


There are a number of tools used to introduce various signals into a broadcast system, and the microphone remains one of the most basic of these input tools in use in radio. The microphone is an instrument used to transduce, or convert, acoustic energy into electric energy. During this process, sound waves are changed into electricity that can then be sent through wires as variations in voltage. There are three types of microphones that are preferred by professionals: moving coil, ribbon, and condenser. These are also often referred to as dynamic, velocity, and capacitor microphones, respectively. Each produces the waveforms that are required for transmission in a different manner.

The moving-coil, or dynamic, microphone is the most widely used due primarily to its durable and rugged design and good frequency response to voices and most music. In this microphone, a flexible membrane, called the diaphragm, is suspended between two electromagnets and is connected to a conducting coil. When sound waves move the diaphragm, they move the coil through the magnetic field. This results in an electrical pattern in the wire that is analogous to the frequency of the sound wave.

The ribbon, or velocity, microphone replaces the moving voice coil and diaphragm with a thin, corrugated metal ribbon that is connected between two poles of a magnet to generate an electrical signal. The incoming sound vibrates the foil, thereby creating the effect. The long, vertical ribbon design of earlier ribbon microphones produced a very lush sound, especially with the human voice, but it was quite fragile and highly susceptible to wind damage. Newer designs use a smaller ribbon that is placed longitudinally between the pole pieces, making this type of microphone more durable and able to withstand louder sound-pressure levels. This microphone was quite common during the "golden age" of radio and is still frequently used in modern recording studios. The printed-ribbon microphone basically operates like the conventional ribbon microphone, but its more rugged design gives it some of the durability of the moving-coil microphone with the rich sound of the ribbon microphone.

Condenser, or capacitor, microphones operate on a different principle from that of the moving-coil and ribbon types. Condensers transduce energy by means of voltage variations instead of magnetic variations. They use a device that consists of two plates—a fixed backplate separated by a small space from a thin, metalized plastic diaphragm. Acoustic energy in the form of sound waves causes vibrations in the diaphragm, which creates voltage changes, varying the signal. These microphones require a power source, so they are usually equipped with internal batteries or with an outside "phantom" power supply. Advances in microelectronics make it possible to make condenser microphones small enough to clip onto a tie or lapel yet still produce a crisp sound. Because they are considered high-performance instruments, they are now the preferred microphones for news personnel.

Two important aspects of microphone technology are impedance and directional characteristics. Impedance is the electric flow resistance of a microphone, which is a factor in its performance. Lower impedance, or lower resistance to signal flow, usually means less interference from extraneous noise such as hum and static. Therefore, better performance can be expected from a microphone with low impedance. Directional characteristics are related to the fact that microphones are designed to pick up sound in varying ways. Lynne Schafer Gross (1986) identifies four basic pickup patterns: (1) unidirectional, which picks up sound mainly from one side; (2) bidirectional, which picks up sound mainly from two sides; (3) cardioid, which picks up sound in a heart-shaped pattern; and (4) omnidirectional, which picks up sound from all directions. The preference for a particular directional characteristic depends primarily on the use of the microphone. Unidirectional microphones are preferred when only one voice is to be picked up. Newscasters and sports-casters, for example, need background noises to be minimized by the single-direction pickup pattern. Bidirectional microphones, which are important for the production of radio dramas, allow actors to deliver their lines while facing each other. Cardioid microphones provide excellent results when two people are speaking side-by-side, such as during a talk show. The omnidirectional microphone is preferable when dealing with a large crowd, such as recording a play with a large cast or recording music that involves a large number of singers or instruments.

Music Sources

The turntable is an input tool that most radio stations no longer use. Those that do still use turntables mostly use them to access their "oldies" music files. Michael Keith (1990) lists the five primary elements of a turntable: (1) a heavy metal plate with a felt or rubber surface to protect the record and prevent slippage; (2) a power switch to control the motor; (3) a gear shift to act as a speed selector; (4) a drive mechanism that turns the plate; and (5) a tone arm or pickup arm that houses a cartridge and a stylus (i.e., a needle). The stylus picks up mechanical (analog) vibrations from the record grooves that the cartridge, acting as a transducer, then converts into an electrical signal. A phonograph preamplifier amplifies this small signal and then sends it to the console for further processing. Turntables were valuable in both production work and in on-air studios from the earliest days of radio broadcasting.

Compact disc (CD) players entered the radio production studio in the 1980s and quickly started to replace the turntable in many stations. Their almost instantaneous appeal was primarily due to superior sound reproduction. CD players offer far greater dynamic range than standard turntables, as well as a lower signal-to-noise ratio. Since the CD is "read" by a laser beam, physical contact is eliminated and distortion is virtually nonexistent. This superior sound performance derives from digital transduction instead of the analog system that is used for vinyl records; far less signal loss occurs. As a result, by 1987, the sale of CDs eclipsed the sale of records, and by 1996, vinyl records accounted for less than 2 percent of music sales. Both the buying public and the broadcast industry were opting for the better sound of digital. This CD dominance was to be of short duration, however; more changes were already on the way.

Just as the CD basically replaced the turntable in the radio station operation, computers have become the music source of preference for many broadcasters. Some stations transfer their music selections directly from CD to hard drive; others may skip the CD altogether and download directly from the music supplier. Another option for many stations is to eliminate in-house music completely. This may be especially applicable for stations that are part of multiple station operations. Music is received, usually by satellite, from outside sources. On-air personalities work from a list of preselected music that is downloaded before their show. That show may be done live, or the on-air personality might lay "voice tracks" (e.g., prere-corded song introductions and other remarks) between the songs in the computer and be at home asleep when the show is actually aired—and the listener will probably never know. The computer software perfectly times the introductions and segue remarks with the music "intro" and "outro" times to form a smooth, seamless programming flow.

Just as it took a while for CDs to replace records, it will be some time before computers completely replace CD players, especially in smaller stations. Economic factors are the primary reason for this delay; it costs more than many small-market stations can afford to completely make the switch. Still, the superior sound quality of digital reproduction will eventually bring about the change. As Joseph Dominick, Barry Sherman, and Gary Copeland (1996, p. 93) point out, "… unlike an analog signal, a digital wave is virtually constant—it is the identical shape on recording, on transmission, in the amplifier, and out of the speakers." Listener demand for digital quality will force technological change, even in the smaller markets. In the long run, the economy of replacing live on-air personnel with computer automation will also reach smaller stations.

Tape Recorders

Another input tool that is still in use but far less than in previous years is the tape recorder. These devices rearrange iron oxide particles on magnetic tape in order to store sound impulses on the tape for playing back later. Stationary heads over which the tape is run do this particle rearrangement. There are usually three heads placed in order to erase, record, and play back. The three basic types of tape recorder used in broadcasting are open reel (often called reel-to-reel), cartridge, and cassette.

One important advantage of the open reel recorder is the accessibility of the tape for editing. Audio editing on this machine usually involves physically cutting the tape and then putting it back together with an adhesive tape. Open reel recorders are available in full-track monophonic (mono), stereo, and multitrack. The four-track is the most common multitrack recorder in radio stations. The advent of digital recording and editing is making the open reel machine only a memory in most radio stations.

Another item that is becoming obsolete at most radio stations is the cartridge machine. At one time, nearly every piece of short production intended for airplay was placed onto cartridge. The cartridge is a container with a loop of tape that varies in length from forty seconds to several minutes. There could be exceptions in length for specific purposes. A cue-tone was placed onto the tape when recording so as to stop it at the beginning of the recording. The machine itself might be a single player or a series linked together in a deck in varying numbers. Some radio stations recorded their music onto cartridges for convenience and to save damaging the vinyl records that were in use at the time.

The third type of tape recorder, the cassette, has more value for on-air play than for production purposes. Many stations still receive programs from outside sources on cassette. News personnel carry the small hand-held recorders to cover stories. Also, copies of advertisements are sent to sponsors on these tapes. Therefore, the cassette recorder may be the one recorder that is the most used by stations. Digital audiotape technology (DAT) has enhanced the usefulness of tape with a smaller cassette that holds more information yet allows a full 48-kilohertz frequency response. The digital signal processing also allows for fast-speed searching, quick cueing, and track programming, among other features.

The Audio Console

The place where all of the inputs meet is the audio console, or control board, as it is more often called. This is the piece of equipment through which all audio signals are processed. It can range in size from as few as five channels with two inputs each to dozens of channels with multiple inputs, looking as complicated as an airplane cockpit. The console has three basic functions: (1) allow the selection of one or more inputs, such as microphone, music, or tape, (2) amplify the sound, and (3) allow the operator to route the inputs to a number of outputs, such as monitors, transmitter, and so on.

A key, or toggle switch, allows an incoming signal to be routed to either an audition or program channel. Channels have volume controls called potentiometers, or pots or faders for short. These control the audio level, or gain, of each amplifier. Pots come in two forms: rotary and vertical slide, with the latter being more in vogue. In addition to individual pots for each channel, there is also a master gain that is usually set by the engineer, a monitor gain that controls the studio speakers, a cue gain, and a headset gain. The output signal is routed to the program amplifier, the final amplification stage before being distributed to a tape recorder or a transmitter.

Monitors, Audio Processors, and Transmitters

The signal is also sent to the volume unit (VU) meter, a device that measures the amount of sound that is being routed through the output of the console. Monitoring audio levels and keeping them consistent from one audio source to another are important in maintaining a consistent station sound. The modulation monitor indicates how the transmitter is performing and can reveal transmitter problems. A stereo monitor helps make sure that the left and right channels are not out of phase, since out-of-phase channels will cancel the majority of the signal in monophonic radio receivers.

Equalizers allow producers to correct problems by boosting and/or cutting frequency lows and highs. Equalizers help create parity between the different elements of production and are useful in creating special effects.

Compressors are used to enhance loudness and eliminate noise. Compression, which can remedy certain problems and get the listener to take greater notice of a piece of production, can make voices sound warmer, production tighter, and levels near perfect. Audio processors can be used to create a wide range of special effects, such as reverberation, echo, and so on.

When the transmitter receives the signal, usually by telephone line or microwave transmission, it is modulated, which means the electrical energy is superimposed onto the carrier wave that represents the frequency of the station. The modulated signal then travels to and through the antenna to, hopefully, many receivers.


As was stated earlier, radio is undergoing much technological change. Digital is thought to be the wave of the future and is already a powerful presence. Computers are replacing many of the input and storage devices in larger stations and will, doubtless, do so in all stations eventually. This is very important to the industry, but from the listeners' standpoint, the quality of what they hear is all that really matters.

See also:Radio Broadcasting; Radio Broadcasting, Careers in; Radio Broadcasting, History of; Radio Broadcasting, Station Programming and; Recording Industry; Recording Industry, Careers in; Recording Industry, History of;Recording Industry, Production Process of; Recording Industry, Technology of.


Alten, Stanley R. (1994). Audio in Media, 4th edition.Belmont, CA: Wadsworth.

Dominick, Joseph R.; Sherman, Barry L.; and Copeland, Gary A. (1996). Broadcasting/Cable and Beyond: An Introduction to Modern Electronic Media, 3rd edition. New York: McGraw-Hill.

Gross, Lynne Schafer. (1986). Telecommunications: An Introduction to Radio, Television, and Other Electronic Media, 2nd edition. Dubuque, IA: Wm. C. Brown.

Keith, Michael C. (1990). Radio Production: Art and Science. Boston: Focal Press.

Montgomery, Ed. (1996-1997). "The Basics of AMRadio" (a twelve-part series that was originally published in Radio World beginning with the Oct. 16, 1996, issue). AMradio/1999/rram2a.html.

Rathbun, Elizabeth A. (2000). "Radio Dreams of Digital." Broadcasting and Cable 30:68-70.

Hal Hughes