The history of the development of radio since its earliest days, when the mere broadcasting of actual sound was miracle enough to create unbounded interest, has witnessed an almost fantastic evolution of technical equipment and technique of operation. Even during the earlier period, when amplifier response and the response of magnetic speakers so limited fidelity capabilities, broadcast engineers recognized the troublesome problems associated with the room or studio in which the program originated. Ordinary architectural construction did not satisfy the requirements for smooth control and faithful reproduction. This led to a detailed study and development of both architectural design and acoustical treatment to suit the needs of broadcasting. Although many experts believe that the final answer to this problem has not yet been found, they all concede that modern broadcast studios have spelled the difference between success and the utter uselessness of high-fidelity amplifiers, microphones, and line or relay links.
There are certain exacting requirements for remote equipment. ( Review Section 8.) The remote operator encounters conditions far from favorable for the type of program to be broadcast. If the specific location produces very decided effects, he must either use them to his advantage or avoid them. It is the purpose of this Section to discuss comprehensively the problems encountered in the best utilization of this equipment to achieve the desired results.
12-1. REMOTE OPERATING PROBLEMS
The remote operator is faced with conditions so varied and complex that any discussion of a specific type of pickup must necessarily present only the general principles involved.
A singer's voice is given a certain timbre by the breath which carries the sound from vibrating vocal chords into the modifying air cavities of the head. As these sound waves emerge, they disturb the air in the place of origin in all directions, but principally in the direction in which the singer is facing. The microphone will pick up the sound anywhere in the room.
Good transmission depends on the position of the performer relative to the microphone and also on the position relative to the walls, floor, and ceiling of the room. The air cavities and acoustical condition of the air boundaries will affect the character or timbre of the sound just as the air cavities of the singer's head determine the original voice quality.
Thus, it becomes apparent that the varied acoustical conditions encountered place considerable importance on the type of microphone to be used and the technique of microphone placement. For example, the operator may find the surfaces bounding the point of pickup to be highly reflective to sound waves, causing distinct "slaps" and echoes to be prevalent. This condition is caused by deflecting surfaces parallel to each other and is the reason why "live-end" broadcast studios are constructed without parallel surfaces. Under this kind of handicap, the operator must use the directional characteristics of the microphone to the best advantage. He could not, for example, use a bidirectional microphone with one live side toward the pickup and the other live side toward a highly reflecting wall.
Due to the nature of remote-control pickups, the microphones used are nearly always of the unidirectional type. This type permits much better discrimination between wanted and unwanted sound, since the noise level at any remote point is quite high compared with a broadcast studio. The uni-directional characteristic is a convenient aid in preventing large amounts of reflected sound-wave energy from actuating the microphone elements.
Since the intensity of a sound wave decreases as the square of the distance, increasing the distance between the sound source and the reflecting surfaces (where this is possible) will decrease the amount of reflected sound-wave energy at the microphone.
By experimenting with the distance between sound source and micro phone, it may be observed that the relationship between original and reflected sound will vary over a considerable range. By decreasing this distance a greater proportion of original sound is obtained, and by increasing the distance (between wanted sound source and microphone) a greater proportion of reflected sound is obtained. Music in particular needs a certain amount of reflected sound for brilliance and color. Too much reflected sound will cause a "hollow" tone and uncomfortable overlapping of succeeding musical passages. If the amount of reflected sound is too small, such as in many studios over treated with sound-absorbent material, the music will be lifeless.
Some of the older-type microphones and remote amplifiers using an unbalanced input (one side grounded) cause a considerable amount of extra work in certain locations where stray ac fields exist near the micro phone or cable. Fluorescent-light circuits in particular are hazards for the remote operator.
When the noise level at a remote setup is noticeable, and it increases with an increase in microphone gain and stops when the microphone is disconnected, the operator must try reorientation and/or changing of the cable runs. Interference from fluorescent lights shows up as a raspy frying noise in the headphones.
At permanent installations using fluorescent lights, where microphones may be placed in proximity, the transformers of the lighting fixtures must be well shielded and placed some distance from the pickup area if possible.
Shielded wires should then connect the fixture to the transformer.
At remote locations where the program is apt to be a one-shot affair, the lighting fixtures must be changed, moved, or turned off during the show.
If this is not immediately possible, the microphone and performers can be moved until interference is eliminated.
The latest remote equipment gives negligible trouble in this respect due to improved shielding of microphones and input transformers, as well as balanced-to-ground circuits.
As stated previously, the problem of broadcasting concerns the transmission and reception of voice and music with the preservation of all the original values. In radio, the degree to which the sound of a performance can play on the emotions of the listener is affected by the transmitter and receiver equipment, studio conditions, and the skill of the engineers. Micro phones and amplifiers today are of such good quality that no practical limitations to true fidelity exist because of mechanical or electrical characteristics. Modern broadcast studios impose only slight limitations on faithful transmission of sound. This emphasizes, insofar as remote broadcasting is concerned, that the skill of the engineer or producer responsible for micro phone setups and operating technique is of utmost importance. This be comes doubly important when it is realized that each orchestra of any type has its own identifying qualities resulting from instrumentation, musical technique, and conductor's interpretations, all under the influencing factor of microphone placement and acoustical conditions of the point of origin.
The effects desired by the orchestra conductor may be achieved only by proper relationship of the microphones to the musical instruments. This proper relationship is directly influenced by the acoustical condition of the pickup area. For transmission of pure musical tones of a violin, the micro phone must be far enough away from the sound holes of the violin that the reflected sounds may be caught fully developed in all their harmonic con tent. Conversely, when special effects are desired, the microphone might be placed near the violin to bring out the harshness of the resin bow drawn across the strings of the instrument.
Perhaps the most striking difference between studio and field pickups is the complete lack of permanent facilities of any kind in the field. The tele phone company will install a broadcast loop on order from the program or traffic department of the station. Sometimes two loops are installed, one to be used as a "talk" line direct to the control room at the studio, or for emergency broadcast service in case of trouble with the regular broadcast line. These lines must be installed as conveniently as possible to the source of the broadcast, yet as inconspicuously as can be arranged. For this reason, it is often a matter of a "line hunt" for the field engineer. This is one reason why he should arrive at the remote point long in advance of broadcast time. The line, or lines, may be found under a table, behind a chair, piano, or organ console and possibly may be in a room away from the main area where the broadcast is to take place. The line is usually tagged with an identifying card.
Since good transmission of talks or speeches from remote points is not as difficult as good transmission of music, the major problems concern the latter. Musical programs may originate at such places as ballrooms, restaurants, night clubs, and cafes featuring dinner music and music for dancing and floor shows. The situation calls for a decided difference in technique of technical production between studio and remote broadcasts.
In the ideal studio musical setup, only one microphone is used at sufficient distance, with the musical instruments grouped and positioned so as to blend into the proper balance at the microphone position. This procedure not only simplifies the problem of control, which always makes for a better effect, but also leaves the problem of orchestral balance in the conductor's hands where it rightfully belongs. Multiple-microphone arrangements place the maximum responsibility for balance of the various sections in the hands of the operator who mixes the outputs of the various microphones.
At remote points, however, where so much activity such as dining or dancing occurs, microphones must be placed close to the musicians. This is inevitable, since otherwise the background noise would result in confusion.
This close arrangement calls for the use of more than one microphone to achieve the desired balance; otherwise the instruments closest to the micro phone would obscure the rest of the orchestra. Then the setup is divided into units of like instruments or combinations of instruments, each unit being covered by a separate microphone so that the volume from each unit may be adjusted at the mixing panel to achieve the desired balance in the combined program signal.
The practice has some advantages for remote pickups other than avoiding background noise. Acoustical conditions that might severely affect the broadcast are minimized to the fullest extent, since the ratio of any reflected sound to the original sound is small. Then too, although some loss of tonal brilliance results from close microphone arrangement, good instrumental definition is gained, which is an important factor for dance broadcasts.
Symphonic music and church broadcasts are different in this respect in that the audience is comparatively quiet, and the pickup area may be treated more as a studio by studying the acoustical conditions existing at the point of origin.
12-2. REMOTE MUSICAL PICKUPS
An observation of Fig. 12-1 will reveal the principles involved in a typical dance-orchestra broadcast. Insofar as the operator is concerned, this setup divides the orchestra into three separate units. One microphone is for the saxophones and clarinets, another is for the trumpets, trombones, and soloist, and a third is for string bass and piano. Microphone number 3 is handy for special emphasis on the rhythm section or for solo passages by the piano or string bass. Note that when the trumpets are open, they are behind the trombones and caught on the second microphone; when muted, they are placed ahead of the trombones and immediately in front of the microphone. Muted trumpets or trombones must be played with the muted bells very close to the face of the microphone. The same is true of any wind instrument on which the player is producing sub-tones. The sub-tones of any wind instrument are just as low in volume, even though open-belled, as the softest muted instrument. This, then, calls for close cooperation be tween the conductor and his musicians and the engineer responsible for proper pickup.
Fig. 12-1. Dance-orchestra arrangement for remote pickup.
Brass Bands
Although brass bands account for a comparatively small amount of radio time, their particular pecularities pose special problems in pickup. A number of community organizations, fraternal societies, and, of course, the armed services participate in radio through presentation of brass bands.
These pickups very often must be made outdoors, the least favorable spot for broadcasting. With no outdoor shell or walls of any kind, no reflection of sound can occur to create the ideal poly-phased sound dispersion so important to broadcasting technique. Under these conditions, it is necessary to use multiple-microphone pickups, grouping the units by means of spotting separate microphones where needed as determined by trial.
For a medium-sized band organization, the units are usually as follows: one microphone for the clarinets, piccolos, and flutes; one for the English horns, bassoons, bass clarinets, saxophones, and tubas; and one for the French horns, trombones, and trumpets. The tympani, traps, and chimes are usually placed in the lower-sensitivity zone of one of the microphones, which prevents the use of excessive distance for proper balance. Indeed, the sensitivity pattern characteristics of the particular microphones used must be thoroughly understood for any kind of musical pickup. Tympani, when used with brass, are predominant in character when placed in a zone where the sensitivity is the same as it is to the rest of the instruments. Just the opposite is true when they are used with strings, since the masking effect due to the characteristics of the musical instruments themselves tends to subordinate the tympani sound.
When well designed outdoor shells are used, the ideal condition exists for brass-band broadcasts. Usually only one microphone is used, suspended some 15 feet out and above the front-line musicians. As before, predominant instruments, such as tympani, traps, and chimes, are placed at the side in a lower-sensitivity area of the microphone.
Salon-Orchestra Remotes
Some dining places have salon or chamber music organizations which are picked up for broadcasting during the noon or early evening hours.
Since a salon orchestra's library contains the more serious type of music, with many low passages, precautions must be taken to subdue the noise of the patrons as much as possible. An intimate microphone placement is therefore indicated under such circumstances.
Usually the chamber group is small, ranging from string trios and quartets to about ten members. For the smaller groups, one microphone raised quite high and slanted down at an angle of about 35 to 45° to the floor is adequate. A hard floor with no covering will aid in obtaining just the amount of brilliance necessary for this type of pickup.
Symphonic Pickups
Symphony-orchestra programs have become a regular feature on the air each season and quite often must be broadcast from a remote point rather than from a regular broadcast studio. Thus far, the musical setups discussed have involved a comparatively small number of musicians and a specific type of instrumental structure. The symphony orchestra, however, is many orchestras in one. The engineer is concerned with the proper grouping of four distinct instrumental sections:
1. Strings: violins, violas, cellos, string basses
2. Woodwinds: clarinets, bassoons, English horns, flutes
3. Brasses: trumpets, trombones, French horns, tubas, euphoniums
4. Percussions: snare drums, bass drums, tambourines, triangles, cymbals, piano, harp, xylophone, marimbas, tympani, etc.
As a general rule, the arrangement of the symphony orchestra for broad cast is the same as for a regular audience performance. The instruments vary in volume of sound produced and therefore in penetrative quality. Strings produce the least volume, then flutes, clarinets, horns, trumpets, and percussion instruments, in that order.
The acoustical situation for symphony broadcasts is generally better than for most other remote pickups, since the auditorium is usually designed for such large groups and made compatible with good listening for the audience, although not always ideal for broadcasting. It is easier from a good transmission standpoint to encounter an auditorium that is too "live" and reverberant so that wall, ceiling, and floor treatments may be added, than to start from one that is too "dead" to produce reflection.
The correct setup for a symphony orchestra is always arrived at on the first rehearsal by trial and error. A number of microphones are spotted at the most likely points so that each may be tried without the commotion of continually moving one microphone. The most likely setup is one micro phone suspended at a height of about 15 feet and about 20 feet in front of the violins. A separate microphone must be used for vocal solos, since a closer relationship of vocalist to microphone must prevail in order to achieve proper balance.
Church Remotes
Programs from churches usually involve both music and a sermon. This ordinarily requires only one microphone when the pulpit is directly in front of the choir, as is the most common church arrangement. When vocal solos occur during the choral rendition, a separate microphone is necessary for proper pickup and balance. It will be noted in nearly all instances that, during solos being picked up by a microphone very close to the choir loft, the organ accompaniment must be brought up to the proper background level by use of the pulpit microphone or a microphone farther out in the congregation. This is due to the acoustical properties which are evident in nearly all churches, causing the organ tones to be much more predominant out in the congregation than up near the choir.
Although it would be impossible to cover all the details and complexities of remote pickups in a single discussion, it is hoped that the picture pre-sensed here sets forth the fundamental procedures that would help to approach a remote problem properly. To present an absolutely complete picture would be impossible, since acoustical conditions and orchestral in tent vary as the number of places from which a broadcast can originate and the number of different music combinations existing. A good understanding of equipment and acoustical variations, however, will enable any engineer to achieve good results with this type of broadcast.
12-3. SPORTS AND SPECIAL EVENTS
There are many types of events with wide public appeal that cannot be covered adequately by the usual methods of remote pickup using wired communication. Among these are various kinds of sports, such as boat racing, cross-country events, and golf matches. Aside from these events, there are the inevitable times of disaster, such as floods, fires, earthquakes, and the myriad catastrophes that wreck ordinary communication services for many miles around the point of trouble. In order to be prepared for eye witness accounts of these happenings, some stations are equipped with portable and mobile relay facilities that are independent of utility companies and any necessary wire lines for relaying the signal to the studio or main transmitter.
There is probably no other division of radio broadcasting that differs so radically from one station to another as the mobile-relay department. Fundamentally, however, the necessary inventory of equipment includes small portable transmitters, wireless microphones, mobile transmitter and antenna mounted in a car or truck, receivers, and power supplies. Typical equipment was described in Section 8.
12-4. LINE ISOLATION COILS AND PADS
Line-to-line coils, usually termed repeat or isolation coils, have numerous uses in the field department of a broadcast station. They are almost a necessity in most instances when an older-type or modified remote amplifier having an unbalanced output circuit (one side grounded) is used. Also, some dubious designs of remote cue-back facilities using an unbalanced circuit will not permit the use of a public-address installation at the remote point without the use of such a coil.
No electrical circuit can be called isolated, since moving electrons cause an electromagnetic field to exist about the conductors. In addition, all conductors have some capacitive effect existent to some point, since, by definition, a capacitor is two conductors separated by a nonconductor.
Consider now the electrical characteristics of the telephone line used to carry broadcast-program currents from studio to studio, studio to transmitter, and remote points to studio. Fig. 12-2A shows the electrical nature of a line operated with one side grounded. Electromagnetic voltages, such as might be set up in the line by adjacent power lines, may be represented by the generator shown in series with the line. Also, since some capacitance exists between the line and ground, any interference picked up by the capacitive coupling may be represented by the generator shown from line to ground. Program currents are shown by solid arrows, induced noise cur rents by dashed arrows. It is obvious that the two currents add together and will be transferred to the input of the transmitter equipment.
Fig. 12-2. Remote telephone lines. (A) Unbalanced. (B) Balanced.
Such lines are not used for broadcast services. Many times, however, the operator is faced with adapting a spare public-address, monitor, or recording amplifier to remote broadcast service. Such amplifiers are almost always of unbalanced-output circuit design, which means that one side of the out put is connected to the chassis or ground circuit of the amplifier. It is also often necessary for the broadcast operator to feed a supplementary public address amplifier at the remote point from the output of his remote amplifier. Quite often this public-address amplifier will use an unbalanced input circuit which, if connected directly to the output of the remote amplifier, will ground one side of the circuit. Either of these conditions will result in effectively grounding one side of the program line.
Telephone lines leased for broadcast services are always strictly metallic circuits (no ground return) , as shown in Fig. 12-2B, which shows the electrical characteristics of the line when balanced transformer windings are used at the terminating ends. It may be observed here that the noise currents from electromagnetic induction and electrostatic coupling are sent along the two wires in the same direction. Their respective directions of flow in the balanced transformer winding at the load end will be 180° out of phase and will cancel out, leaving only the program currents. In some circuits, the center tap of the windings is grounded; in the majority of circuits, however, the center tap is ungrounded.
Connections to Unbalanced Circuits
Whenever it is necessary to use an unbalanced output circuit to feed a program line, an isolation coil should be used. This coil may have an impedance ratio of 600 to 600 ohms, or 600 to 150 ohms if the line to be fed is quite long. Such a mismatch as this provides a beneficial equalizing effect to compensate for the usual high-frequency attenuation of the line.
At remote points where it is necessary to feed a public-address amplifier by direct connection, and the input circuit is unbalanced, the same type of coil should be used for the line connection. This permits the grounding of one side of the remote amplifier without disturbing the balanced line conditions.
As mentioned earlier, some remote cue-back circuits at the studio end are unbalanced. Such a circuit is not normally important, since it is used only as a cue device. Consider, however, a case in which it is necessary to feed the public-address amplifier with the cue-back signal from the studio.
This often occurs during certain types of programs in which it is important for the audience at the remote point to hear signals from the studio. Obviously, the unbalanced line signals will not be of a quality suitable to feed the pa system due to hum and noise on the line. Here it is necessary to use the coil as shown in Fig. 12-3, both at the sending and receiving ends of the line, so that balanced line conditions prevail.
Fig. 12-3. Isolation-coil circuit.
Output of Remote Amp Isolation Coil Line
Program Line Levels
Program signal magnitudes on broadcast lines must be high enough to override the noise level, but they must be limited to prevent cross-interference into other lines by electromagnetic and electrostatic coupling. The maximum level permitted in most states is +12 VU into the sending end of the line. The normal level is +8 VU. The multiplier switch is set to +8 so that 0 indication on the meter is referenced to +8.
The broadcast engineer faced with adapting spare amplifiers for remote amplifier purposes must keep this maximum level in mind. Public-address, monitoring, or recording amplifiers generally have an output far in excess of allowable broadcast line levels. For this purpose, pads must be designed as outlined in Section 6.
12-5. BELL TELEPHONE AND AT&T LINE SERVICES
The characteristics of various wire services available to the broadcaster are defined by the FCC tariff tables. Where customers have special or un usual requirements, the telephone company will work out services tailored to their needs.
Broadly speaking, services are classed into two main types:
1. Lines for continuous use, such as a studio-to-transmitter feed
2. Lines for occasional or one-time-only use, such as those ordered for remote pickups Continuous-use lines are classified as follows:
Schedule AAA (frequency range of 50 to 15,000 Hz) Schedule AA (frequency range of 50 to 8000 Hz) Schedule A (frequency range of 100 to 5000 Hz) Occasional-use lines are classified as follows:
Schedule BBB (same frequency range as AAA) Schedule BB (same frequency range as AA) Schedule B (same frequency range as A) When a network of stations is interconnected, involving reversals of trans mission direction at operating centers, special charges and rules apply.
The services listed are high-quality lines for full- and part-time use.
They are amplitude and delay equalized for broadcast-program transmission over long distances from point of origin to studio. There are also several services of lower grades (C, D, and E) available to the broadcaster.
Such services are designed for telephone communications and consequently make use of telephone-type amplifiers and repeat coils. In the case of these lines, accumulation of objectionable noise and delay distortion occurs over relatively short distances. Since remote-broadcast applications require that the line transmit in one direction only ( thus eliminating the need for balanced configurations), small improvements in effective bandwidth may be made by the telephone company. Even with such adjustments, however, these lines are still restricted to short-distance use. This service is often used to save cost in the coverage of sporting events and similar programming for which wideband characteristics are not necessary.
EXERCISES
Q12-1. What is the basic difference in microphone setup for programs involving music at a remote location and in the studio?
Q12-2. You are feeding a balanced program line from a remote location, and it is necessary simultaneously to feed a public address amplifier that has an unbalanced input. What do you do?
Q12-3. You have a remote pickup at an airport, and you are picking up voice transmissions from the control tower. What can you do to minimize this
Q12-4. What can be done at the studio to improve transmission from a remote pickup employing low-grade line service?