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article number 470
article date 07-30-2015
copyright 2015 by Author else SaltOfAmerica
Magnetic Sound Recording Part 2; We Develop Magnetic Tape - Broadcast Industry Adopts Recording, Late 1940’s
by John Regnell

From the author’s 1957 Master’s thesis.

EDITOR’S NOTE: Nearly all of the many references are left out of this casual reading article but we do occasionally include special unpublished ones which indicated the dedicated research of the author. Of course, the author had the advantage of living at the time of historical magnetic recording developments so he was able to obtain personal interviews, letters and mimeographed documents.
* * *

D. Manufacturing the Tape

1946 was a decisive year in the magnetic recording field. Mr. Mullin’s demonstrations plus articles written about the German recorders had stirred wide interest.

In May of 1946 four men from Armour Research organized Magnecord, Incorporated in Chicago to produce a high-fidelity wire recorder for radio station use. They were J. S. Boyers, R. L. Landon, R. J. Tinkham, and C. G. Barker. Their model SD-1 wire recorder sold for $1500 and ten were sold the first year.

Both Ampex and Ranger were working on tape machines and Brush already had its Sound Mirror tape recorder in production on a limited scale. However, wire recording was far in the lead.

Regardless of the ascendance of wire recording, a decision was made at Minnesota Mining and Manufacturing company in St. Paul to investigate the magnetic oxide for coated tape.

After comparing German tapes, Brush paper tape, and the experimental 3M tape, it had been decided that a superior tape could be made if the oxide material could be improved. Up to that time all the oxide had been supplied 3M by Brush Development, Armour Research, and some which had been supplied by commercial sources.

There were three problems involved in using German tapes.
1. The output was low and elaborate and expensive amplifiers were required to produce a satisfactory signal.
2. The tape had poor response at short wave lengths which necessitated driving it at high speeds of thirty inches per second (compared to seven-and-one-half inches per second today) to maintain adequate frequency response.
3, The uniformity of German tape varied widely and made standardization of equipment and recording procedures difficult.

All other oxides available were found wanting in one or more of the important magnetic properties determined to be essential in a good magnetic tape.

These properties included good frequency response, maximum signal-to-noise ratio, high signal output with minimum distortion, and ease of erasure of the recorded material. With these characteristics guiding research, 3M eventually arrived at the particular gamma ferric oxide which is now employed in virtually all the magnetic tape made in this country.

Magnetone (Model BK-303 ) portable wire recorder. (Courtesy of The Brush Development Company.)

At this point 3M began to contact the manufacturers of tape machines in an effort at standardization, since it would be necessary for full development of the industry. Reel sizes, machine speeds and equalization were only a few of the problems which had to be agreed upon.

Problems in production of tape in late 1946 and early 1947 were many. Slight coating speed changes or adjustments resulted in excessive coating weight variations which actually were in the audible range.

To maintain a coating uniformity of plus or minus ¼ db. means the coating thickness could not vary more than 0.00001 (one hundred thousandth) of an inch. Tape width was exacting too, and clean-cut edges on the tape were necessary to prevent its lifting from the recording head and causing drop-outs in the signal.

The first 3M tape went on sale in 1947 and used a paper backing as did the Brush magnetic tape. The black oxide used had the technical description Fe3O4.

It offered greatly improved performance over the German tape with nearly twice the coercive force and thus the ability to retain it magnetic pattern indefinitely. More significantly, it could be played at slower speeds with high quality.

After the introduction of the black oxide paper tape, 3M soon followed with a plastic tape, The extremely smooth acetate backing was a decided improvement over the comparatively rough paper surfaces used previously.

E. Bing Crosby Enterprises

Early in 1947, Bing Crosby Enterprises sent a man to San Francisco to Palmer Films for some work on an industrial film which they were making. There he saw the Magnetophon and the work Mr. Mullin and Mr. Palmer were doing with it, editing and splicing tape sound tracks and indicated that it was just what Mr. Crosby was looking for.

Mr. Crosby was attempting to do his radio program for Philco on discs rather than doing it live. This meant trying to edit several short recordings into a single half-hour disc for the show and involved dubbing from disc to disc and sometimes twice-removed dubbing before it went on the air.

During the season, thirty-nine such editing jobs had to be done. Technical problems were so great that it looked for a time as if Mr. Crosby would have to give up the recording idea and go back to doing his shows live.

Mr. Mullin was then introduced to Frank Healy of Bing Crosby Enterprises and then to Murdo McKenzie, technical producer for the Crosby Show.

In June, 1947 Mr. Mullin and Mr. Palmer demonstrated the two Magnetophons for the Crosby people. Mr. McKenzie was quick to realize that he could never do on discs what Mr. Mullin was doing so easily in editing the tape.

However, Mr. McKenzie had heard about a demonstration made by Colonel Ranger and his new Rangertone recorder in New York at ABC late that spring and suggested that the Ranger machine should be tested, too. As a result, Mr. Mullin agreed to have his machines there for another demonstration in August for the first Crosby show in the fall of 1947.

However, the question was raised as to what would happen if the two Magnetophons were to break down during the recordings. There were no replacements. To solve this problem, Mr. Mullin contacted Colonel Ranger and told him of this opportunity to sell Mr. Crosby on taping his program.

Colonel Ranger agreed to have two of his Rangertone machines in Los Angeles for the August demonstration for Mr. Crosby. The result of this demonstration was that Mr. Mullin was hired by Crosby Enterprises to tape the shows for that entire season. Colonel Ranger contacted other Los Angeles firms and demonstrated his machines for them.

The Rangertone magnetic tape recorder. (Courtesy of Rangertone, Inc.)

After Mr. Mullin recorded the Crosby programs and put them together on tape, he transferred them to discs, since at thirty-inches-per-second tape speed, the tape would only carry a twenty-minute recording. He only had fifty reels of German tape, however, and this was another problem.

The publicity resulting from his Magnetophon demonstrations had prompted both Minnesota Mining and Manufacturing Company and Audio Devices to submit tape samples to him for testing on the Magnetophon, but no satisfactory tape for Magnetophon use had been produced in quantity.

In the fail of 1947, however, 3M developed a new red oxide which is used in nearly all magnetic tape today. Its technical description was Fe2O3, and it offered a 14 db. output superiority over the German tapes.

The new tape on an acetate plastic backing was so superior that it had the same 15,000 cycle frequency response at seven-and-one-half inches per second as the Magnetophon and tape had at thirty inches per second.

This cut tape cost 75% and increased playing and recording time nearly 200%.

Furthermore, the new red oxide tape could be erased and re-used repeatedly without a tendency toward permanent magnetization. Because the particle size was better controlled, it had a more uniform signal output.

An indication of the significance of the new red oxide magnetic tape is provided by the reaction of Magnecord, Inc., who had been making high-fidelity wire recorders for broadcast use.

Then in late 1947 came the news. Instead of wire, Minnesota Mining and Manufacturing Company had perfected a tape that was capable of high fidelity, 15,000 cycles per second, which has become a broadcast standard. Although magnetic tape had been on the market before, it had been capable of low quality recording only.

Since this new plastic tape was much easier to edit, splice together, store and handle generally broadcasters and other professional users soon came to demand it.

Magnecord switched to tape.

A delegation from 3M went to Los Angeles to show the new tape to Mr. Mullin and Crosby Enterprises and to Ampex at San Carlos. However, the characteristics of the Magnetophon, and of the Ampex 200 recorder were such that the 3M product would not produce best results.

Therefore, since they could not convince Mr. Mullin or the Ampex people to modify their machines, 3M decided to make a special tape patterned after the German type L which would satisfy the requirements of thirty-inches-per-second operation.

The next problem of Crosby Enterprises was how to get more tape recorders. Mr. Mullin began to work more closely with Ampex Electric in order that they might have a successful recorder on the market as soon as possible.

Although tape had made progress in 1947, wire recording still dominated the market almost completely. Some seventeen firms were producing wire recorders while only four— Rangertone, Brush, Amplifier Corporation of America, and Sound Recorder and Reproducer Company—were producing tape machines.

Experimental Armour dual-channel tape recorder. (Courtesy of Armour Research Foundation.)

Early in 1948, 3M marketed a new red oxide tape which made possible high fidelity recording even at three-and-three-quarter inches per second and slower. With this tape, 3M contacted machine manufacturers and interested them in designing low-cost recorders which could be built taking advantage of this new tape’s characteristics.

However, after 3M filed a patent application on its red oxide tape, it was learned that an application had already been filed on the same oxide and tape by Marvin Camras of Armour Research Foundation and that Mr. Camras had made the invention before 3M.

Accordingly, the patent on this oxide and recording tape was issued to Amour Research Foundation. This patent, U. S. Patent Number 2,694,656, was granted on November 16, 1954 to Marvin Camras. Minnesota Mining is a licensee of the Armour patent.

In April of 1948, Bing Crosby Enterprises became a distributor for the new Ampex machines and the first shipment of the new tape for the Magnetophons arrived in Los Angeles.

The first Ampex machines did not record. They were playback units. When they were employed on the Crosby show the Magnetophons still were used for the recording and the Ampexes for playback.

The first demonstration of the Ampex was conducted in April of 1948 at NBC studios in Hollywood to record Crosby’s ABC program. That demonstration prompted Middlebrook, ABC vice president in charge of engineering, to buy twelve of the Ampex 200’s at $5200 each, and then twelve more.

John Mullin with Ampex magnetic tape recorders packaged for travel.

ABC’s move was a major step in the acceptance of magnetic recording. Their techniques in using the equipment are discussed later.

Subsequent Ampexes included the record feature, and were modified to operate at slower speeds using the regular red oxide tape rather than the tape patterned after the German material.

A guaranteed supply of tape recorders and magnetic tape was now available, and the spread of tape recording in broadcasting and elsewhere was rapid. The May 28, 1948 issue of Variety states:

“Tape has in the past year completely changed not only the operation on top ABC shows but has altered the thinking of the entire industry regarding recorded programs.

“When the Crosby show first went on ABC two years ago it was strictly a transcription job of dubbing and editing, and re-dubbing and re-editing, often requiring as many as four days after a show was originally cut on platters before it was whipped into broadcasting shape.

“Then tape was used. At first it was transferred to platters for broadcast because equipment hadn’t been perfected for broadcasting directly from tape. This method was still better than the previous year’s because there was only one transfer instead of six or seven, with the consequent loss of quality in each step.

“Time necessary for editing the show to its final broadcast form was reduced to a mere three or four hours when tape was first tried last fall, following a summer of intensive experimenting by both ABC and the Crosby office. Continuity editors, operating in the same manner as film editors, have now reached the point where they can wrap up the job in two hours.

“Program edited on the original tape is now being aired. It retains the original broadcast quality.

“It’s so good that in a recent demonstration for engineers from Southern California stations, a live program was recorded simultaneously on tape and the experts weren’t able to tell which was tape and which was live as the control-booth engineer switched from live pickup to tape pickup.”

By late spring of 1948, John Mullin retired his Magnetophons which were still in excellent condition, from the broadcast operation and returned them to work in the Palmer Film studios.

It was these machines more than any other which had led the revolution in recording for broadcast purposes.

Also by the spring of 1948 one of the Rangertone tape recorders had been put to work by Standard Radio Transcription Services.

One use was to obtain more realistic sound effects recordings. A battery-operated tape recorder operating at a tape speed of eighteen inches per second was used in planes, trains, even submarines, any place where two men could carry two units the size of large suitcases.

By November of 1948 the three professional tape recorders in use were the Ampex, the Rangertone, and Magnecord. Minnesota Mining and Manufacturing Company and Brush Development Company had been joined by Indiana Steel Products Company in the making of coated, magnetic tape.

By 1950, Audio Devices, Inc., New York; Fidelitone, Inc., Chicago; and Orradio Industries, Opeleika, Alabama, had produced magnetic tape for general sale. Approximately thirty-three tape recorders by twenty-four manufacturers were on the market at that time.

Presenting the new Ampex Magnetic Tape Recorder ... the great new unit that put the Crosby Show on tape.


With the development of machines and tapes to a frequency response and dependability which could be considered as professional quality, came the adoption of the medium by the broadcasting industry. Another important item in this adoption was the guaranteed supply of equipment and tape.

The industry has utilized the medium primarily for delayed broadcasting and pre-broadcast production.

A. The Use of Magnetic Tape for Delayed Broadcasting

Although all of the major radio networks eventually adopted magnetic tape recording for delayed broadcasting, the American Broadcasting Company was the first to exploit its possibilities in this way. The solutions which ABC found for its delayed broadcasting problems are essentially the same ones which were subsequently used by all networks.

In addition to the commercial networks’ use of tape, the National Association of Educational Broadcasters developed a tape network to facilitate programming on its member stations.

1. Networks

The seasonal adoption of daylight saving time by the major cities during the summer months creates a problem for the radio networks. The portions of the country which do not adopt daylight time must be supplied with network programs at their accustomed times to avoid confusion, loss of listeners, and loss of sponsors who have spent the winter months building an audience for a particular time segment.

a. The American Broadcasting Company

In 1946 ABC and Mutual recorded some programs as broadcast on daylight time and played them back an hour later for the stations on standard time. In 1948, NBC and CBS adopted the practice for all regular network shows.

Prior to this time, it was the practice of the networks to record the programs for the areas remaining on standard time on acetate discs. Obviously this type of operation required the use of large quantities of discs with their attendant storage problem and high cost. In addition, the recording and playback machines needed frequent service to maintain them in proper operating condition.

A bank of recording machines of the disc type also requires a considerable amount of space.. Until 1948, the American Broadcasting Company did none of their own recording, preferring to have this work done by independent companies equipped to handle this operation.

The method of recording and playing back for a different time zone in network operation has the effect of doubling the number of networks and substantially increasing operating costs. The sixteen-inch acetate discs which were used cost about $8 for one half-hour program. Magnetic tape of the plastic variety cost only $4.50 for a half-hour program, and could be used and re-used almost indefinitely.

Thus, with the advent of high quality tapes and tape recorders, several of the problems were automatically solved. Tape machines had the advantage of requiring little service except routine maintenance, and the tape could be used over and over, with a very low coat per recording and no storage problem.

Top view of Ampex magnetic-tape recorder. The various functions of the instrument are controlled by push buttons (1) . The capstan is driven by a hysteresis synchronous motor. The take-up (2) and supply reel (3) are driven by motors so designed as to provide relatively constant torque independent of diameter variations of the reels.

The head assembly has a sliding front, the position of which is controlled by the handle (4) on the rear of the head housing (5). When the gate (6) is closed, the recording medium (7) is given a slight wrap around the pole pieces of each of the three ring heads — the erasing, the recording, and the reproducing head.

With the gate open, the tape is disengaged from contact with the heads so that it can be moved at high speed without head wear. (Courtesy of Ampex Electric Corp.)

The fidelity of tape greatly exceeded that obtained with the best disc equipment, and recordings of almost any length could be made with no interruption. A standard sixteen-inch disc could only record slightly over fifteen minutes of program before it was necessary to change machines. Quite often it was difficult to time the disc to place the end of a recording at a point where the continuity was not disturbed.

The American Broadcasting Company was the pioneer in the use of magnetic tape for delayed broadcasts in the United States, and, beginning on April 25, 1948, the network recorded and played back on a one-hour delay basis, the eighteen hours of daily program material routed through its Chicago studios.

Equipped with ten Ampex tape machines, the Chicago studios relied primarily on six units mounted in consoles for the bulk of the recording. By means of a switching system, any machine could be selected for either record or playback.

All recording and playback was made in duplicate to insure against equipment failure. Experience proved that this feature was seldom needed. In feeding a program to the network, two machines with duplicate tapes were run in synchronization.

The master machine fed one line while the safety or emergency machine was feeding the second line and was pre-set to feed the first line in the event of failure, simply by means of pressing an “operate” button on any control panel. Each machine was equipped with its own control panel and monitor speaker.

The tape equipment was installed in the spring of 1948, and in two years of operation it had been in use for approximately 7100 hours. During 1948 the total time lost due to tape breakage was only three minutes or .002%. No time was lost during 1949.

b. Other Commercial Networks

The Columbia Broadcasting System, after its experience of recording the New York State political conventions in 1946 was quick to see the advantages of tape in special events. However, CBS did not use it for delayed network. operations until 1948. The National Broadcasting Company adopted tape recording slightly later than the other networks. For many years it was the policy of NBC to provide as much live program material as poesible.*

* Letter from George K. Graham, National Broadcasting Co., RCA Building, New York, New York, August 6, 1956.

c. The National Association of Educational Broadcasters

In 1949, the National Association of Educational Broadcasters began the program exchange using magnetic tape recordings which was later called “the bicycle network.” Station WNYC, New York City, made five sets of recordings of the 1949 Herald Tribune Forum which were distributed to and aired by twenty-two NAEB member stations.

By 1950 the “bicycle network” had advanced to the point where several stations agreed to exchange programs by tape recording. Seymour Siegel, Director of WNYC, recorded several programs from the New York area for distribution, and the Association received a gift of tape from the Cooper Union for use in the project.

By May, Siegel was able to report that the “network which is enjoying enormous growth, will soon be able to furnish four hours of programs per day to member stations, and will include selected programs from BBC and CBS as well as excellent offerings from member stations and institutions.” This operation, though considered to be a function of the NAEB, was actually carried out by Siegel and, his WNYC staff with little outside assistance or financial aid.

Magnetic tape in the recording studio.

By late 1950, the tape network, which had begun as an experiment had grown to the point where it had outgrown its facilities and financial structure. It now served thirty-four member stations.

Dean Wilbur Schramm of the University of Illinois proposed a plan whereby the NAEB network could locate at the University of Illinois and could be financed and supported by a series of special grants in addition to the specific contributions of housing and personnel that the University would be willing to make.

In May, 1951, largely through the efforts of Dean Schramm, a grant was received from the W. K. Kellogg Foundation to cover a 5-year period in financing a headquarters organization for the NAEB, and for establishing an NAEB tape network. The terms stipulated that over the five-year period the network would gradually become self-supporting.

Richard Rider, of the University of Illinois, was appointed network manager. He had earlier been named to manage the tape network during the interim period before the network and headquarters operations had been formalized.

In July of 1951, the network. was serving sixty educational non-commercial stations, and within a few months the number had risen to approximately eighty. The program material which was submitted for distribution by the network came from member stations as veil as from the British Broadcasting Corporation and the Canadian Broadcasting Corporation.

The duplication of the tapes was done three at a time on Magnacorders by the University of Illinois Recording Service, and stations ordering specific programs were arranged on five "legs" of the network. The program was sent on tape to the first station on the leg and would subsequently be “bicycled" by mail from one station to another in time for broadcast.

At this time the network owned about 6,000 twelve-hundred-foot reels of tape, and was able to circulate six to eight series of thirteen programs during each quarter of the year.

In January of 1952 the network instituted the “package" system of distribution. Through this method all programs for a given week were mailed together to the first station on the leg. This station would use whichever of the programs it desired during that week and send the complete mailing on to the next station.

This system had the advantage of keeping the offering together and resulted in less confusion in mailing of tapes between stations. Also in 1952, the network purchased two Ampex recorders for the purpose of making master tapes of the best possible quality from the programs which were submitted by member stations.

In order to do away with the "bicycle" type of distribution of programs, it was necessary for the network to increase the speed with which the programs could be duplicated. By late in 1953, two mass duplicators, specially designed by the L. S. Toogood Recording Company for the network were put into service. Each machine could duplicate eleven programs at triple speed, which made it possible to mail the programs to each individual station as they were ordered.

Currently, the NAEB network distributes eight to ten hours of programming a week to about eighty educational stations.

These figures do not include programs designed for classroom use which represent about seven more series of programs of thirty programs each. This operation involves the dubbing and mailing of approximately 800 to 1000 tapes each week, and it is accomplished by a staff of five full-time and one half-time employees.

Interior of the Ampex magnetic-tape recorder. For easy servicing, the different electronic sections are connected to each other and to the drive mechanism by means of plug connections. (Courtesy of Ampex Electric Corp.)

According to a study of the NAEB Research Committee, the member stations of the NAEB have a potential audience of eighty million; half the population of the United States, plus parts of Mexico and Canada.

The sources of programs for the network in addition to member stations have included: American Foundation for the Blind, UNESCO, the American Society of Friends, the Cooper Union Forum, and the Air Training Command. Other sources have been the British Broadcasting Corporation, the Canadian Broadcasting Corporation, Radio-Italiana, and the French Broadcasting System.

According to Harry J. Skornia, Executive Director of the NAEB:

“All in all the NAEB Network is providing an essential service to the educational broadcasting services of America, and an organization with which European stations can exchange ideas, publications, personnel, techniques, and programs. . . . it has become a model for installations in many other parts of the civilized world.”

Thus, it becomes clear that magnetic tape recording made possible the growth of educational broadcasting in the United States in a way which would have been impossible using disc recordings. The NAEB network is the only educational network in the world, and it was made possible through the use of magnetic tape.

Indeed, many leaders in the field of educational broadcasting have stated that the establishment of the tape network has been the one most important contribution to the advancement of educational broadcasting in the United States. Without it many stations would be forced off the air.

2. Delayed Broadcasting at Radio Stations

Radio stations as well as networks became interested in the use of magnetic tape for delayed broadcasting.

In the network affiliate station conflicts which might occur between a scheduled network program and a local special event, problems were easily resolved. The network offering was delayed by recording it on tape for later broadcast, while the special event was broadcast in its place.

Disc recording had never been successful for this purpose because of its high cost and low quality in terms of frequency response.

B. The Use of Magnetic Tape for Pre-Broadcast Production

Pre-broadcast production is meant here to indicate any recording or editing activity which is accomplished in order to, in some way alter the program content, prior to its broadcast. Such activity includes eliminating errors, building programs, and automatic station operation.

Ampex ad: 100,000 hours of commercial use proves its dependability and service.

1. Eliminating Errors

As Bing Crosby found early in his use of tape recording, the facility with which slips or errors on the part of talent can be corrected is one of the important benefits of tape. There have been many instances repeated as to the talent of editors in the technique of cutting and splicing tape, but the one which follows seems to be outstanding, since it involves music.

On New Year’ a Day in 1949, the regular Saturday broadcast of the Metropolitan Opera was cancelled so that the Sugar Bowl football game could be aired. Rather than disappoint the millions of opera lovers, the client and the network tape recorded the program and scheduled its broadcast for the following afternoon.

During the performance, the title-role prima donna broke rather badly on a certain E-flat in “Lucia’s” mad scene. The unmistakable break was bad enough in the opera house, but the prospect of broadcasting it was nearly too much to face.

The engineers, having detected the bad spot, cut it out with a pair of scissors and replaced it with another E-flat from an entirely different aria which the singer had managed beautifully. The Sunday broadcast of “Lucia” was sent out free from blemish.

2. Building Programs

Program building using magnetic tape became a technique which greatly improved the quality and availability of program types. Procedures used in both studio productions and remote productions are now indispensable to radio broadcasting.

a. Studio Productions

In addition to the facility with which errors could be eliminated from program content, magnetic tape enabled producers to prepare perfected entertainment. Bing Crosby was in the habit of recording forty minutes for his thirty-minute program. In this way he could cut "soft spots" and any bit of continuity which did not come over as planned.

This procedure also allowed the program to be recorded at the convenience of the artists concerned, and allowed for ease in scheduling of studio facilities.

b. Remote Productions

The uses to which NBC applied magnetic tape in remote productions are representative of the industry.

1. Assembling of documentaries. This would include programs in which excerpts from a number of recordings would be combined to make one program. These recordings would normally have been made at various locations.

2. Remote pick-up. This involves any use of portable equipment in a special events situation. The recorders can range from standard portables to the miniature wire and tape recorders which are spring driven or battery operated.

The 1946 New York State political convention was covered by the Columbia Broadcasting System using Brush Sound Mirrors. The recordings were made at Saratoga and played back from Albany. The entire day and night proceedings were recorded and subsequently were edited to a fast-moving program without all the convention delays and roll-calls.

Portable Soundmirror, Model BK403. (Courtesy of the Brush Development Company.)

As a result of this experience, a group of Brush tape recorders were installed in a tape cubicle adjacent to the CBS News department in New York City. These machines were used to pre-record transatlantic news broadcasts when the overseas circuits were at their best and the commentators were available.

These tapes were then used during regular broadcasts. From this their use spread to remote pick-ups on which disc equipment had previously been used, and, eventually, to the use which Crosby had introduced in preparing his programs.

CBS also makes a very specialized, though not unique, use of tape by recording famous symphony orchestras and concerts in Europe. James Fassett, CBS director of serious music, spends a great deal of his time in Europe obtaining this special material for broadcast in this country.*

* Letter from Davidson M. Vorhes, Manager of Radio Technical Operations, CBS Radio, New York, New York, August 1, 1956.

Network newsmen carry the extremely portable personal tape recorders overseas with them to interview key personalities in the news.

As was indicated by the network usage and figures, tape was relatively cheaper to use than disc recordings, but the machines as of 1948 were still very expensive. Ampex, which made the biggest set on the market, was only turning out one a day, at $4,000 each.

However, machines such as the Brush Sound Mirror in portable size were selling for $229.50, and a New York company had a make-it-yourself kit or $100.

During this period when professional-type recorders were relatively unavailable and quite expensive, quite a number of home recorders were released.

These home recorders, because of their low cost, necessarily had many of the more desirable features and circuit refinements omitted. However, with refinements added, they approached the professional quality.

A number of these medium and low-cost recorders were purchased by individual broadcast stations for interim use until the more professional units could be obtained.

Generally the program material involved in these uses was of a news or special events nature since with the use of tape, it became more easily attainable.

On a purely technical basis, advantages found early to recommend tape use in place of discs were the following:

- 1. Most machines feed the tape past the heads at a constant velocity under control of a synchronous motor. Therefore, a uniform program fidelity exists. Disc systems incur translation losses through cutting and playback.
- 2. Program frequency range is greater than disc, and the noise level a lower.
- 3. Tape can be recorded, played back and erased, and used over.
- 4. Considerably less audio power is required for tape than for disc recording, and a chip-suction system is not required.
- 5. Continuous monitoring of the recording on the tape can be maintained on professional machines since they are equipped with separate record and playback heads. If close spaced, the monitoring delay is about 1/30 of a second at higher tape speeds.

In using the modified home-type recorders for broadcast purposes in local stations, the operator would merely plug the recorder into one of the remote repeat coils, and bring it in as he would normally do for a remote broadcast.

Frequency response of Rangertone magnetic recorder. (From "Magnetic Tape Recorder for Movies and Radio,” by. R. H. Ranger, "Electronics,” Oct., 1947.)

3. Automatic Station Operation

One of the most successful broadcasting applications of tape recording is possible at the network affiliate station. Here, the tape playback of station breaks and spot announcements has proven to be a great help to the local station.

By this method, it was found that an announcer could assemble the entire day’s between-network breaks in less than one hour. This left the rest of the day for the preparation of local programming.

Furthermore, the announcer need not be on duty during the entire broadcast day or on week ends, making it possible to cut down on numbers of announcers and to increase quality.

However, this kind of operation places increased responsibility on the technical staff of a station, since the control room engineer has complete control of running the proper spot at the proper time.

One of the most current refinements of the above system is being implemented by the Ampex Corporation and features increased operating efficiency through the use of automatic controls. The system permits automatic, non-attended broadcasting of program schedules as long as 18 hours. Program material quality is in every way identical to a live broadcast.

Announcements and program selections can be alternately played, and every thirty minutes a station break can be interposed. Following the station break, the succeeding half-hour program will start in perfect synchronism with real time.

The equipment necessary includes two long-playing playback units, one for program material and one for announcements, one machine for recording, and two special components. One of these special units over-sees the operation of the system during playback; the other is a recording console for the voice recording.

In operation, the program machine plays the first selection. At the end of the selection the control tone from the music tape energizes relays that shut down the program machine and start the announce machine. At the end of the announcement, the control tone on the announce tape shuts down the announce machine and starts the program machine. This operation continues for the greater part of the time involved.

In addition, the system includes a "master-timer" which insures that it will operate on correct Western Union time, and compensates for any errors in the machine or tape.

In preparing the announce tapes, the following technique would be used in the case of a music program:
- The number of musical selections fixes the number of breaks in which announcements will be placed.
- Total running time of the music fixes the minimum time which must be consumed by the announcements.
- The combined running tine of music plus announcements should be 29:45.
- The announcer, in preparing the announce tape, starts the recorder and begins reading the announcements.
- At the end of each announcement, he presses the tone-button, and the 25-cycle control tone is automatically recorded for a fixed interval.
- All announcements may be recorded without stopping the recorder.
- If no announcement is to be made following a selection, the announcer places the tone on the tape. Then, during playback the system will automatically continue on to the next selection.
- The system can be modified to operate a multiple record changer so the latest record releases can be used.

C. Miscellaneous

Many uses of magnetic tape were developed as aids to the broadcasting industry which did not contribute directly to program production.

Station operators soon learned that the portable tape equipment was useful for presenting programs to potential advertisers. Sample programs were made up for specific merchandisers, and the salesman would take the recorder and play the sample program to the prospective advertiser during his interview. Early results obtained in using the recorder in this fashion were highly satisfactory.

Underneath view of drive mechanism of BK-411 Soundmirror. The motor (1) is resiliently mounted and is energized by electrical switch (2) when lever bar (3), through rotating arms (4) and (5) , disengages one or the other clutch. Small flywheel (6) , rotating with a speed of about 1,650 r.p.m., provides sufficient mechanical filter action. (Courtesy of The Brush Development Company.)

On the network level, other uses of tape include:
- 1. Sound effects. In addition to the recording of special sound effects, tape is used in much the same manner in which discs were used formerly.
- 2. Reference Record. The recording of shows on tape for reference purposes for use by clients or production personnel.
- 3. Phonograph records. Magnetic tape is used for the recording of material which is later to be transferred to master discs for use in the manufacture of phonograph records.

In television production, two uses of magnetic audio tape became important at a later stage:

- 1. Pre-recording. An artist might be required to sing and dance or make other movements which would make a good sound pick-up difficult. The artist records the song under optimum conditions and during the actual performance would "mouth" the words.

To some extent this same technique has been used with orchestras where the music is recorded in advance. The orchestra plays during the on-the-air shows to provide the pictorial element but the audience actually hears the pre-recorded version.

- 2. Thought sequence. In some technical productions an artist may be required to coordinate facial expressions with a "thought" sequence which the audience hears. This is done by pre-recording the required material in the artists voices sometimes using echo chambers or other sound effects techniques. The recording is then played back at the appropriate time. Somewhat similar use occurs during certain types of puppet shows where the puppet voices or human voices on the show may be recorded and intermingled as required.

With an understanding of the above techniques, it becomes obvious that magnetic recording has developed into one of the most valuable tools available to the radio broadcasting programmer. Considering the way in which radio broadcasting operates today, it might even be said that magnetic tape is practically indispensable.


The National Association of Radio and Television Broadcasters contributed materially to the standardization of recording and reproducing characteristics of audio information on tape.

In 1949 the National Association of Broadcasters (the name was subsequently changed to include television) adopted and promulgated the industry’s first set of recording and reproducing standards. Subsequently, these standards were revised in accordance with developments in the technique. The most recent substantive changes in these standards occurred in 1953.*

* Letter from Joseph M. Sitrick, Manner of Publicity and Informational Services, National Association of Radio and Television Broadcasters, July 18, 1956.

The recording and reproduction of audio material involves the balancing of three basic qualities:
- frequency response,
- distortion, and
- signal-to-noise ratio.

If lower distortion is desired it usually means recording at a lower level, thus sacrificing signal-to-noise ratio. Noise level can be reduced if the frequency range is restricted. Thus, all of the elements have an inter-relationship.

Iron-cored magnetizing unit for obtaining hysteresis and derived curve of magnetic tape samples, circa 1957. (By courtesy of Wireless World.)

The standards set up by the NARTB apply only to the tape, so that any tape can be used in any machine. Actually, in view of the variation between recording heads, the recording and playback section of tape recorders varies between manufacturers.

Even though there is such variation, all still follow the NARTB standard in that the characteristic of the recorded material on the tape is the same, irrespective of the machine used.

The NARTB equalization standard was developed with the philosophy that the intelligence on the medium is the most important point to standardize, since it is the item that is transferred from one machine to another. These standards are considered the optimum, and are used throughout the world. Information published by the NARTB also includes a list of definitions and appropriate nomenclature used by engineers in the recording field.

BING! . . . Bing Crosby brought magnetic tape technology into the studio. Ten years later he led innovation in video taping.
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