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03. Radio Studio and Production Systems

3.1 Radio Studios
       A radio station produces on air programs with one or more live presenters and guests in a studio at the station, playing music and other program segments from various devices, and taking phone calls on the air. When needed, the On-Air studio operator also selects another studio in the building or selects a feed from a remote source and integrates that source into the on-air program. Nowadays, the process is largely automated, and whole programs may be broadcast without the intervention of a live presenter.

3.1.1 Studio Characteristics
       The audio production studio is a physical room that has an impact on the sound produced in it. Because of this, several characteristics of sound should be considered in designing the studio, including sound isolation, noise and vibration control, and room acoustics. When sound strikes a surface either the studio wall or the floor, some of that sound is reflected while some is absorbed within or transmitted through the material of the surface. Most of the sound that hits a hard, flat surface will be reflected. However, if the surface is irregular, it will break up the sound wave and disperse the reflections, known as diffusion. Sound that's absorbed into the surface is dissipated within it, but penetration occurs when sound goes through a surface and is transmitted into the space on the other side. When a sound is produced, the direct sound is the main sound that we hear.
       In a production situation, it is sound that goes from the sound source straight to the microphone. On the other hand, indirect or reflected sound reaches the microphone fractions of second after the direct sound does because it has traveled a circuitous route. Reflected sound consists of echo and reverberation. Echo is the indirect sound that has bounced off or been reflected from one surface. Similarly reverberation is the sound after reflecting from two or more surfaces before reaching the microphone. Echo provides a distinct repetition of the sound such as "hello __ hello __ hello." On the other hand, a reverb is repeated reflections and provide a continuous decay of the sound, such as "hello __ oo __ oo." The components of direct and indirect sound make up what is commonly called the sound's life cycle. In designing the audio studio, the goal is to manipulate these sound characteristics to create a proper sound environment for production work.
       When considering reflected sound, we think in terms of reverb time and reverb route. Reverb time is the time that is takes for a sound to die out or go from full volume to silence. Reverb route is the path that sound takes from its source to a reflective surface and back to the original source. Excessive reflected sound tends to accent high and mid range frequencies which produces a harsh sound. Reflected sound can also be reinforced sound. It may cause objects or surfaces within the studio to vibrate at the same frequencies as the original sound. Both absorption and diffusion are used to control reflected sound. Part of the reflected sound can be absorbed within the carpeting, curtains and walls of the studio. Absorption soaks up sound and shortens reverb time to prevent excessive reflection. Absorption provides a dead studio having a very short reverb time and a long reverb route. In contrast, a live studio has a longer reverb time and a shorter reverb route that produces more gleaming sound.
       Diffusion uses irregular room surfaces to break up sound reflections. This decreases the intensity of the reflections making them less noticeable. The sound reflections here are redirected rather than soaked up. Most studio design control reflections by a combination of absorption and diffusion techniques. Audio studio utilize soundproofing to accomplish sound isolation. Soundproofing keeps penetration of outside sound minimum form entering the studio and inside sound from escaping form the studio. Doors are heavy-duty and tightly sealed. Windows are often double-glassed with the interior pane slanted downward to minimize reflected sounds. Furthermore, walls, ceiling and flooring are covered with special sound-treatment materials.

3.1.2 Radio Air Chain      
       A radio station has two kinds of studios: on-air and production. Both share basic design features and have comparable equipment. The standard equipment found in radio studios includes an audio console, computer workstation, speakers and reel-to-reel tape decks, cartridge players, compact disc players, mini-disk players, digital effects boxes and a patch panel.
       A station's air chain is the path that its on-air program materials follows from the program source to the transmitter. The arrangement for a local radio station on-air studio and air chain up to the studio-transmitter link (STL) will be as shown in figure 3.1.

       Microphones and other program sources feed into an audio mixing console. The output of the console will usually pass through various items of audio processing equipment that adjust the overall sound of the station and then to the STL for sending to the transmitter.

3.1.3 Audio Console
       The audio console, also called a Mixer, is the very heart of a radio station. Different manufacturers produce audio consoles, and although design characteristics vary, the basic components remain relatively similar. Console come in all different size and shapes and may be monaural, stereo, multi-track and digital. They contain:
- Input that permit audio energy to enter the console.
- Outputs through which audio energy is fed to other locations.
- VU meters that measure the amount or level of sound.
- Faders that control gain or the quantity of sound.
- Monitor gains that control in-studio volume.
- Master gains used for the purpose of controlling aggregated output levels.
       One common type of VU meter has a moving needle on a calibrated scale. Usually the top position of the scale is calibrated in decibels (dB), and the lower portion of the scale is calibrated in percentages. In audio engineering, a reading of 0 dB is 100 percent volume. Mixers also have amplifiers at various stages so that the signal is loud enough when it eventually goes to the transmitter. These amplifiers are covered inside the mixer. In addition, audio console can have many other features to help the operator work more efficiently and creatively.
       Any control board has three primary functions such as mix, amplify and route audio. First, the audio console enables the operator to select any one or a combination of various inputs. Audio consoles are referred to as the mixtures because of their ability to select and have several inputs operational at the same time. It has controls that allow the operator to select each source and feed one or more simultaneously to a mixed program output called a bus. Each input has a level control known as a fader.
       Amplifying the income audio signal to an appropriate level is the second function of the control board. Although all sound sources are amplified to a degree, some sound sources produce such a small electrical current that they must be further amplified to be used. The third function of the audio console is to enable the operator to route the inputs to a number of outputs, such as monitor speakers, or the transmitter. This function allows the operator to determine where the signal is going and to provide a means for listening to the signal. Figure 3.2 shows a type of such an audio console.
Figure 3.2: Digital Audio Console
       Mixer inputs are two main types: microphone and line inputs. Each feeds a channel on the mixer. Microphones have very small analog signal outputs and require sensitive channel inputs. Most other equipment and distribution system provide audio at a much higher line level. On an audio console, a channel refers to a group of switches, faders and knobs that are usually associated with one or two sound sources. Individual input selectors, output selectors, volume controls and on/off switches are also associated with each individual channel. The board also produces a mix minus version of the program to send back to telephone callers. This contains the complete program but without the contributor's own audio. Another function found on most audio mixer is called cue or prefade listen (PFL) monitoring, which allows previewing an input sound source. In the cue position, the audio signal is routed to cue amplifier and then, normally to a small speaker built into the console.
       The most common arrangement for the output selectors on an audio console is series of three buttons for program, audition and auxiliary outputs. When no button is pushed in, the output is stopped at this point. When the program button (PGM) is pushed, the signal normally goes to the transmitter if the console is in an on-air studio or to an audio recorder if the console is in a production room. Some audio console include a master fader that controls the volume of the signal leaving the board. A stereo console requires two masters.
       Audio boards are often referred to by their number of inputs and outputs, so a 16-in/4-out board has 16 inputs and 4 outputs. Many sound console include simple equalizers (EQ). These increase or attenuate certain frequencies, thus altering the the sound of the voice or music by changing its tonal quality. The input signal of the analog channel is split into three frequency ranges: high, midrange and low. Some mixers have a built-in tone generator. This reference tone generally used for checking the audio level and placed on an audio recording before the actual program material.
         A few boards have a talk-back switch, which is a simple intercom system consisting of a built-in microphone and a push-button control that turns the microphone on or off. The normal position of this switch is off so that the button must be pushed in to activate the microphone. The signal from the talk-back microphone is sent to a speaker in another studio. It allows the operator at the audio console to communicate with the announcer in a studio at a separate location.

3.2 Analog Recording Devices
3.2.1 Turntable
       The turntable was the first piece of analog equipment used in recording industry. Its function relate only to playing back sound material because a turntable cannot record. The two basic functions are to spin a record at the precise speed at which it was recorded, and to convert the variations in the grooves of the record to electrical energy. The main parts of most professional turntables include a platter, an on/off switch, a motor, a speed selector switch, a tone arm, a cartridge/stylus and a pre-amplifier. The disc known simply as records were of two different formats and were made of less breakable vinyl and had smaller grooves. One was 7 inches in diameter, played at 45RPM, and held about 5 minutes per side. The other was the long-play(LP) record, which was 12 inches, operated at 33-1/3 RPM, and could hold about 30 minutes per side. Turntables were developed with a speed selector switch that controlled the speed of the motor to support these various formats. Figure 3.3 shows a Denon made turntable.
Figure 3.3 Turntable Machine
3.2.2 Reel-to-Reel Tape Machines
       These machines have three magnetic heads whose purpose it is to record sound, playback sound and erase magnetic impressions from recording tape. Most reel-to-reel machines are capable of recording at two speeds. The tape speeds most commonly available on broadcast quality, state-of-the-art reel-to-reel machines are 71/2 and15 inches per second (IPS). The speed 71/2, is used most frequently by broadcasters. Reel-to-reel recorders, also called open-reel, have 1/4 inch recording tape. They are most useful for recording and playing back long programs. Editing of program material is carried by actually cutting and splicing the tape. The system records stereo channels using two parallel tracks on the tape. Reel-to-reel tape machines are available in monaural, stereo and multitrack. The last allows for overdubbing or sound-on-sound recording, which gives the producer greater control over the mix of sound elements. This machine shown in figure 3.4 is becoming less important in studios as a result of digitization.

Figure 3.4 Open Reel Tape Recorder
3.2.3 Cassette Tape Recorders
       Cassette recorders employ 1/8-inch tape that is moved at 17/8 IPS. Cassette tapes can hold up to three hours of material. Cassettes are useful piece of studio equipment though not as popular as mini-disc and CD machines. On-air cassette machines, shown in figure 3.5, generally are used to play music, features and actualities. Cassette tape recorders came in stereo and monaural and were available in everything from pocket-sized portables to permanent rack-mounted models. This tape is housed in a plastic case that slips into the recorder.
Figure 3.5 Cassette Tape Recorder

3.2.4 Cartridge Tape Recorders
       Cartridge machines use a cartridge with an endless loop of 1/4 inch tape inside. They are useful for playing short program segments, such as commercials, fillers. The audio tape cartridge is constructed as a plastic container with a continuous loop of tape inside. The tape pulls from the inside and winds on the outside of the spool. Their big advantages are simple push-button controls, nearly instant start, and the use of cue tones. These tones signal the beginning and end of a recording. Few types of the machines are shown in figure 3.6
Figure 3.6 Cartridge Tape Recorders
3.2.5 Telephone Hybrids
       The interface to an analog telephone line to be used on-air requires a device called a telephone hybrid. This piece of equipment converts incoming audio from the phone line into a line level signal that can be fed into a mixing board. It also converts a line level signal coming out of a mixing board into an audio signal that can be fed over the phone line back to the caller. The hybrid allows the caller to be heard on air, and also allows the anchor to hear the caller without having to pick up a telephone handset. At the same time, it allows the caller to hear the anchor and the rest of the program. It ensures that only the caller's voice is of telephone quality, while the program anchor's voice remains of broadcast quality.
Figure: Telephone Hybrid
3.3 Digital Recorder/Players
3.3.1 CD Players
       The compact disc player was the first piece of digital equipment to be embraced in audio production and broadcast work. It is still one of the key sources for playing back prerecorded material. The internal structure of the CD player centers around three major components: a drive motor, a laser and lens system, and a tracking mechanism. The drive motor spins the disc at a constant rate, the drive motor slows down as the laser moves to the outside the disc. A compact disk is 4.7 inches wide and 1.2mm thick. A CD stores music as 16-bit digital words with the standard sampling rate of 44,100. Around 650MB (Megabytes) of data is stored on a standard 74-minute CD.
       Besides CD players, different companies offer CD recorders that work in the CD-R and/or CD-RW format. CD-R(CD-recordable) is a write once, read many design. The CD-RW (CD-Rewritable) disc is used in a similar fashion, however, the record can be erased and the space on the disc can be reused for recording other materials. It is shown in the figure 3.7.
Figure 3.7 Compact Disc Player
3.3.2 The MD Recorder/Player
       Originally developed by Sony as a digital replacement for the cassttee, the MiniDisc (MD) can be a handheld, tabletop or rack-system. The MD can hold up to 80 minutes because of a data compression scheme. It is permanently sealed in a plastic cartridge, so it can be handled without worrying about dust or fingerprints. The MD comes in both a prerecorded and recordable format. The actual disc is about 2.5 inches in diameter. MiniDisc (MD) recorders and players of different styles and applications have seen moderate success in the audio production studio.

3.3.3 DAT Recorder
       The actual Digital Audio Tape (DAT) cassette tape consists of two small tape reels encased in a plastic housing. The DAT recorder used technology based on traditional cassette recorder, and CD player. The DAT system records with the help of rotating heads and encodes digital data on 1/8-inch tape in a series of diagonal tracks. DAT recording is 16-bit at sampling rates of 32, 44.1 or generally 48kHz. DAT, like CD, had several controls for selecting specific songs on the tape.

3.3.4 Compact Flash and Other Digital Recorders
       Nowadays, the digital recorders used in audio production work are solid-state recorders. They record on a removable media card, such as a Compact USB ports. A 1-GB card can hold over 1 hour of uncompressed stereo audio or up to 36 hours of MP3 mono audio. A flash recorder has inbuilt digital recording microphone with 1GB of recording memory. A single button initiates recording with a high-quality omnidirectional or cardioid mic-capsule or external line input. They have analog and digital audio input and output connections. They can be connected to a computer or audio workstation for file transfer. Thus, they can be used as stand-alone record/replay devices or as acquisition devices for a file server.
Figure: 3.8 Compact Flash Recorder
3.4 Microphones
       Microphones (or Mics) convert sound waves created by human voices, instruments, or other things into electrical signals. In audio production, microphones are also used to record voice, music or sound effects in both the studio and the field. There is no one correct microphone to use in audio production work, but specific types of microphones work better than others in certain situations. Microphones are usually categorized by two key specifications, their electrical operation and their pickup pattern. Classified by their internal, sound-generating element, there are two types of microphones commonly used in audio production work: the dynamic microphone and the condenser microphone.

3.4.1 Dynamic Microphone

       In this moving coil microphone, a diaphragm is exposed to the incoming sound pressure waves in the air and moves backward and forward in a corresponding manner. The back of the diaphragm is connected to a metal coil that slides up and down over a small magnet. The coil movement over the magnet causes an electrical signal to be created in the wires in the coil. This signal is a reproduction of the sound waves that hit the diaphragm. The ends of the coil are connected to the plug on the end of the microphone, and the signal can be fed from there to a mixing board. The dynamic microphone is a good general-purpose microphone commonly used in radio and audio production studios and has many advantages that make it popular. It is a modestly priced microphone that produces very low self noise and has excellent frequency response. But the main reason it has seen such acceptance by broadcasters is its robust design. The strongly designed microphone can withstand extremely high sound levels. Fairly insensitive to wind along with its ruggedness, it is an excellent remote or field recording microphone. The main disadvantage of the dynamic microphone is that it does not satisfactorily reproduce certain frequencies.
Figure 3.9 Block Diagram of a Dynamic Microphone
 3.4.2 Condenser Microphone
       The condenser microphone operates using a principle based on the operation of a capacitor. The sound-generating elements consists of a charged conductive diaphragm and an oppositely charged metallic backplate separated by an insulating material. An air space is created between them and that forms a sound-sensitive capacitor. The metal-coated plastic diaphragm and the backplate. This alteration changes the capacitance and generates a small electrical signal that is further amplified within the electronics of the microphone. This fluctuation of electrical current is the audio output signal. Condenser microphones utilize small internal power supplies or phantom power supplies. The phantom power usually comes from a recorder or an audio mixer through the microphone cable and back to the microphone. The condenser microphone is much smaller and lighter than dynamic mics. It produces excellent sound quality and wide frequency response. It is fairly rugged but can be distorted at high recording volumes. The built-in microphone on many portable audio recorders is often a condenser microphone.
Figure 3.10 Block Diagram of a Condenser Microphone
3.4.3 Microphone Pickup Patterns
The pickup pattern is the other way of classifying microphones. The directional response of a microphone indicates how sensitive they are to sound from varying directions around the microphone. The directional response of a microphone is recorded on a polar diagram. Microphones can be constructed so that they have different directional characteristics. They come in four main pattern types.

- Omnidirectional Mic
The omnidirectional microphone picks up sound from all directions. They are commonly used outside the studio when the ambience of the location needs to be picked up along with a person's voice. Bidirectional microphones pick up almost equally in the front and back.

- Cardiod Mic
The cardiod or unidirectional microphone mic picks up sound mainly from one direction. It has strong pickup on the axis of the microphone, but reduced pickup to the side and to the back. This provides a heart-shaped pattern calling it a "cardioid".

- Hypercardiod Mic
By changing the number and size of the openings on the case, it is possible to increase the directionality of a microphone. This further reduces sensitivity to sounds on the back and sides.

- Shotgun Mic
The shotgun is a highly directional microphone. There are a number of applications that require an even more highly directional microphone, such as in news gathering, wildlife recording etc.

- Lavaliere Mic
Extremely small tie clip microphones are known as lavaliere mics. They are usually electrets condenser and omnidirectional. These mics are generally designed to blend in with an article of clothing.

The Pressure Zone Micropone (PZM) is designed to decrease the amount of echo or reverberation when recording in large room. PZM microphones, which are omnidirectional, are flat and designed to be mounted to a wall or placed on the floor or a tabletop.

- Wireless Mic
A wireless microphone system consists of three main components: an input device, a transmitter and a receiver. The input device provides the audio signal that will be sent out by the transmitter. It may be a microphone such as a handheld type or a tie-clip type. The transmitter handles the conversion of the audio signal into a radio signal and broadcast it through an antenna. The job of the receiver is to pick up the radio signal broadcast by the transmitter and change it back into an audio signal.

- Stereo Mic
Stereo microphones are essentially two microphones in a single casing or body. These are designed primarily for ease of placement, since the body is considerably smaller than two separate microphones.

3.4.4 Microphone Specifications
- Sensitivity
This is a measure of how much electrical output is produced by a given sound pressure.

- Overload Characteristics
Any microphone will produce distortion when it is overdriven by loud sounds.

- Frequency Response
A flat frequency response has been the main goal of microphone companies. Many mics have a deliberate emphasis at certain frequencies because that makes them useful for some applications.

- Noise
Noise in a microphone comes in two varieties: self-noise generated by the mic itself and handling noise. In addition to the basic microphone, following accessories are necessary for proper audio production work: windscreens, shock mounts and stands or booms.