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von Masanori Kimizuka in 2012

The history of sound recording started with the "Phonograph," the machine invented by Thomas Edison in the USA in 1877. Following that invention, Oberlin Smith, an American engineer, announced his idea for magnetic recording in 1888. Ten years later, Valdemar Poulsen, a Danish telephone engineer, invented the world's frst magnetic recorder, called the "Telegraphone," in 1898. The Telegraphone used thin metal wire as the recording material. Though wire recorders like the Telegraphone did not become popular, research on magnetic recording continued all over the world, and a new type of recorder that used tape coated with magnetic powder instead of metal wire as the recording material was invented in the 1920's.

The real archetype of the modern tape recorder, the "Magnetophone", which was developed in Germany in the mid-1930's, was based on this recorder. After World War II, the USA conducted extensive research on the technology of the requisitioned Magnetophone and subsequently developed a modern professional tape recorder.

Since the functionality of this tape recorder was superior to that of the conventional disc recorder, several broadcast stations immediately introduced new machines to their radio broadcasting operations. The tape recorder was soon introduced to the consumer market also, which led to a very rapid increase in the number of machines produced.
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In Japan, "Tokyo Tsushin Kogyo" (eine Gründung von Masaru Ibuka und Akio Morita), which eventually changed its name to SONY, started investigating magnetic recording technology after the end of the war and soon developed their original magnetic tape and recorder. (Anmerkung : Darum hier gleich mal der Verweis auf Akio Moritas Biografie)

In 1950 they (SONY) released the first Japanese tape recorder. In the 1960's several cartridge-type tape recorders (Anmerkung : Das waren Recorder für die amerikanischen 8-track Cartridges) were developed to meet the requirements of car-stereo devices, and finally, the (Philips) compact cassette system was introduced.

Japanese manufacturers contributed to improving the basic recording performance of compact cassette recorders and to expanding the variety of available products, especially small-sized tape recorders. As a result, they attained a large market share in the worldwide tape recorder market.
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In 1979 the "Walkman," a portable compact cassette player, was introduced to the market, and in a very short period it became very popular all over the world. The product concept of the Walkman was well accepted, and it changed the style of audio listening dramatically.

In this report I briefly describe the history of sound recording, particularly the progress and relation of magnetic recording technologies in the compact cassette system. I also describe the product concept and downsizing technologies of the Walkman.

In the last section, I explain the development of digital audio tape (DAT), an advanced tape recording system from 1986 that led to the rise of digital audio technology.

Japanese audio manufacturers joined the tape recorder market relatively soon after the end of World War II. Around 1970 the technical capabilities of device manufacturers increased rapidly, and many superior devices such as precision mechanical components and high-performance electrical devices became available on the domestic market.

The synergy effect between product design and device technologies improved the competitiveness of the final products, and Japanese audio manufacturers achieved success in the compact cassette tape recorder market. They changed the style of listening and the audio product itself with their introduction of the stereo-headphone "Walkman" in 1979. They ultimately succeeded in getting a huge market share of the worldwide audio market.

Many people have recently been enjoying listening to music supplied in a digitally compressed format with small portable devices and headphones. However, it is hoped that the Japanese audio industry will develop a revolutionary new product or service for a more comfortable listening experience with even better sound.
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Many thousands of years ago, people painted various images on rock surfaces. The vivid animal depictions in the famous Cave of Altamira, thought to have been painted as a ritual to the gods, are still-image records left by the people of the time.

Since ancient times, people have dreamt of recording sound in the same way as pictures; however, they lacked the means to record it, other than passing it down through the oral traditions of story and song. When writing was invented, people could record their voices through this innovative means of “recording words using letters”. With regard to music, however, capturing the sound itself held more signifcance than the recording of mere words. People devised notation systems as a means to record the sounds of music and a number of civilisations had their own notations and symbols for this purpose. However, this “sheet music” was still an indirect means of recording music. The recording of sound itself remained a dream.

Around the mid-19th century, Frenchman Édouard-Léon Scott de Martinville devised a machine that could record the changes in a sound waveform against a time axis, based on the idea that sound is transmitted as a wave.

Although Scott de Martinville’s machine could record sound waveforms, it could not reproduce the recorded waveform as sound.

In 1877, around 20 years later, American inventor Thomas Edison invented the “phonograph”, a machine that could reproduce sound by producing a vibration from a sound waveform recorded on a brass cylinder wrapped in tin foil.

For the frst time in human history, a machine could record and reproduce sound. The more advanced gramophone record was a later improvement to the device. This advancement meant that the device could be developed not only as a sound recorder, but also as a household music player through these records.

As radio broadcasting gained popularity, disc recorders became vital pieces of equipment for recording and playing back sound, used by many broadcasting offices until the end of the Second World War.

While records improved in quality, increased in length and progressed to stereo, the principle of sound recording remained the same: mechanically recording or etching raw sound waveforms onto media.

Telecommunications technology developed rapidly in the 19th century and telegraphy became increasingly more practical. In 1876, American inventor Graham Bell invented the telephone, which could transmit sound itself.

Based on the idea that telephonic sound is converted into electricity and could thus be recorded in the form of magnetic changes, American Oberlin Smith published the world’s frst article on the concept of magnetic recording.

In 1898, inspired by this concept, Danish engineer Valdemar Poulsen used steel wire to build the “Telegraphone” wire recorder, the world’s first practical magnetic recording machine.

Just before the Second World War, a magnetic recording machine was proposed in Germany, which replaced the steel wire with tape, making it easier to use. This was the birth of the prototype tape recorder. While the war prevented countries from exchanging magnetic tape recording technology, research progressed in Germany and the technology continued to improve.

By the end of the war, the tape recorder was complete, equipped with advanced technology such as AC bias and stereo recording. After the war, the Allies carried out a detailed investigation of all German technology related to magnetic recording; this technology then became widely used in the development of tape recorders in the United States.

Ampex, a small, newly-founded company, took on the challenge of developing the tape recorder in the United States; before long, it was an industry-leading corporation, making major contributions to the technical advancement and development of the tape recorder.

With Europe lagging a little behind the times, Studer, a small Swiss company, began to develop the tape recorder there. It developed superior models, from business machines to luxury consumer products, and became the leader of the industry in Europe. In Japan, Tokyo Tsushin Kogyo (later Sony), founded not long after the end of the war, persevered in researching magnetic recording, believing in its potential.

In 1950, the company completed the first domestically-produced tape recorder in impoverished postwar Japan. After the war, tape recorder technology and its potential star qualities went public. Venture companies in Japan, Europe and the United States alike took on the tape recorder challenge, and a number of interesting designs emerged.

While tape recorders first gained popularity for business use, companies soon began to develop models for general use as well, and these machines quickly gained popularity for household use. In the United States, they became the popular choice of audio equipment for entertainment with the sale of music tapes, which had converted to stereo much faster than records had. Companies began to focus on easy-to-use cartridge-style tape recorders, with car stereos as a possible application.

In the early 1960s, companies began to propose multiple-cartridge systems. A compact cassette proposed by the Dutch company Philips established itself as the effective global standard with a royalty free patent licence policy.

By this time, Japanese companies were becoming more confident in their development and design of AV equipment. Parts manufacturers, who supplied electronic components and equipment parts, began to improve their technological capabilities, developing better quality and more advanced parts and actively working to incorporate them into their designs.

Like the compact cassette tape recorder, technological developments were standardised, high in performance and packed with features. This work required perseverance and meticulous attention to detail, but Japanese companies were well suited to this and ended up leading the compact cassette tape recorder industry.

At the same time, other audio equipment also began to be sought after around the world. The 1970s and 1980s ushered in a golden age for the Japanese audio industry. Given the popularity of compact cassettes, the headphone-equipped portable stereo, the Walkman, appeared in 1979. This embodied a completely new audio concept. Music, which had previously been limited to within the home, could now be taken outdoors and enjoyed alone anytime, anywhere. This hit product swept the world, causing a revolution that fundamentally altered the way we listened to music.

This report begins with the history of sound recording, and then touches on the invention of magnetic recording and the development of the early open reel tape recorders in Chapters 2 to 5, before going on to discuss the development of component technologies of the compact cassette tape, such as tape, heads, noise reduction and motors in Chapters 6 to 12.

Chapter 13 describes the development of compact cassette equipment and the creation and development of the Walkman, the headphone-equipped portable stereo. Chapter 14 describes the development of digital audio tape recorders (DAT), typifed by the compact disc, at the leading edge of technology in the digital audio age.
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Writing was invented as human civilisations developed, making it possible to record and pass on various matters. As writing developed, it enabled large amounts of knowledge to be kept on a broad range of areas for a long period of time, facilitating the further advancement and expansion of civilisation.

From the dawn of time, writing (and pictures) by humans was the sole means of keeping records. It was the dream of humankind since ancient times to store and reproduce voice and music, or the sounds themselves, but this dream was not readily achieved.

Much trial and error took place in the 19th century to achieve this dream based on rapidly advancing modern science and technology, and some major results had been achieved even before the advent of the 20th century.

Sound is a wave that travels through the air; it is a compression wave that alters with time. Accordingly, in order to record sound, it is necessary to record the changes in that wave against a time axis.

Based on the idea that sound could be recorded if air density could be captured as an oscillation, French printer Édouard-Léon Scott de Martinville succeeded in recording a waveform in 1857.

His device captured sound through a plaster horn and transmitted it to a diaphragm; a pig bristle attached to the diaphragm recorded the sound waveform in lampblack onto a cylinder. The cylinder was turned on its axis with the sound waveform recorded in a continuous line on the surface of the cylinder.

This instrument was named the phonautograph; many of these were manufactured as experimental equipment for sound recording (Fig. 2.1). A further improvement was made to the device by wrapping it with paper coated in lampblack, which could then be kept as a recording paper, rather than coating the cylinder itself.

While the phonautograph could record sound, it could not play it back, as it had no means to reproduce the original sound from the waveform. However, it excited many scientists and engineers, who became engrossed in trying to invent a machine that could record and play back sound.

In 1877, 20 years after the phonautograph was invented, American inventor Thomas Edison succeeded in making a device that could record and play back sound using a cylinder like the phonautograph.

The cylinder was made of brass, wrapped in tin foil and fitted with a handle on its axis. Cylindrical tubes fitted with diaphragms with needles attached were arranged on either side of the cylinder. These tubes worked respectively as a microphone for recording and a speaker for playback.

To record sound, one pressed the microphone needle against the cylinder and wound the handle. When one spoke into the microphone tube, the needle would record the sound on the tin foil on the cylinder. To play the sound back, the needle on the playback diaphragm would trace the groove created during recording; the diaphragm would vibrate according to the recorded waveform and convert it back to sound.

This was a very clear and simple mechanism. Edison immediately decided to apply for a patent, naming this instrument the “Phonograph” (Figs. 2.2, 2.3).

While it seems to have been based on the idea of Scott de Martinville’s phonautograph, it was full of original ideas and experimentation, such as using tin foil as a recording media and the unique construction of the diaphragm and needles.

The phonograph finally achieved the dream of recording sound for the first time in history. The invention of the “talking machine” immediately became known throughout the world, as did the name “Phonograph”.

It appeared in an article in a Japanese literary magazine the following year in 1878 with a translated name meaning “voice reproduction device”.

In 1879, Englishman James Ewing, a lecturer at the University of Tokyo, carried out a public experiment for himself. The president of the Tokyo Nichi Nichi Shinbun newspaper, Genichiro Fukuchi, who attended the experiment, coined the Japanese term chikuonki meaning “sound storing device” that later took hold in Japan as the name for the gramophone.
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There was much interest in the gramophone at the laboratory (later Bell Laboratories) founded by Graham Bell, the inventor of the telephone. Researchers at the laboratory hoped to study improvements to the gramophone; one of these was Emil Berliner.

Berliner moved to the United States from Germany at the age of 19 and worked as a technician on research to improve the gramophone. He was greatly impressed and excited by Edison’s cylinder phonograph and had a good understanding of its inherent issues.

Edison’s device recorded sound by etching a waveform onto a cylinder in a vertical direction (die Tiefenschrift), with the depth of the groove changing with the volume of the sound.

Feeling that this would distort the sound, Berliner came up with a system of etching the waveform in a horizontal direction (die Seitenschrift).

Berliner also came up with the idea of using flat, disc-shaped recording media instead of cylinders.

Thus, the disc gramophone and gramophone records were conceived in 1887, 10 years after Edison’s phonograph. This instrument was named the “Gramophone” (Fig. 2.4), marking a very significant point in the history of sound recording.

Berliner did not stop at simply inventing the gramophone, he also devised the basis for the business model of reproducing recorded discs and selling them in large quantities as records.

Creating a mould (eine Form oder Vorlage) by carefully reproducing a groove etched (geritzt) into a master disc then using that mould to produce large quantities of copies was the prototype for modern record production. This was vitally instrumental to the development of the recording and music industries.

The discs were far more suited to the reproduction process than were the cylinders; this became the trump card to conclude the market battle between the two formats. These records were the mainstay of recorded music until the late 20th century.

Technical improvements to disc records continued to develop, such as long-playing capabilities, improved sound quality and stereo sound, although the principle of producing sound by mechanically tracing a groove etched onto a disc remained fundamentally the same as it had been in Berliner’s gramophone.

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Edison had turned humanity’s dream of recording sound into reality. Berliner had improved on the cylinder phonograph, creating the disc gramophone. The invention of the gramophone had implications that went beyond merely recording sound; it created an industry from a new style of entertainment in the form of listening to music at home on duplicated records.

The underlying principle of the gramophone was that of mechanically recording a sound waveform onto a medium and reproducing that waveform as an oscillation. Around 1888, American mechanical engineer Oberlin Smith devised and published an idea for a device for recording voices transmitted by telephone based on a completely different principle from that used in the gramophone.

Inspired by the phonograph, Smith was the frst in the world to come up with the idea of magnetic recording, which differed completely from mechanical recording methods.

Believing that more information could be gathered by making this available to the general public, he published his idea in "The Electrical World" without patenting it. The concept of magnetic recording published by Oberlin Smith is given below.

“The following proposed apparatus is, however, purely electrical, and is, as far as known to the writer, the only one fulflling such conditions that has been suggested. [Fig. 3.1 (a)] is the recording part of an electrical phonograph. [Fig. 3.1 (b)] is the talking part of the same. Many of the pieces, as D, E, B, C, etc., can be the same ones as are used in [Fig. 3.1 (a)]

In [Fig. 3.1 (a)] the voice or other sound is delivered into an ordinary telephone A. Preferably, this should be a carbon transmitter so as to have s battery F in the circuit, and thus use as strong a current as practicable. Possibly, however, a Bell telephone without a battery would answer the purpose.

In either case the current, broken into waves of varying lengths and intensities corresponding with the vibrations of the diaphragm in the telephone, passes in its circuit through the helix B, converting into a permanent magnet any piece of hardened steel which may be at the time within the helix.

Through this helix B passes a cord, string, thread, ribbon, chain or wire C, made wholly or partly of hardened steel, and kept in motion by being wound on to the reel E from off the reel D, E being revolved by hand, clock-work or other means. J is a tension spring or brake pressing against D to keep the cord C taut.

When in operation with the undulatory current from the telephone A passing through the helix, the cord C becomes, so to speak, a series of short magnets grouped into alternate swellings and attenuations of magnetism. The actual lengths of these groups depends upon the speed of their motion, but their relative lengths depend upon the relative lengths of the sound wave; and their relative intensities depend upon the relative amplitudes of these waves.

The cord C therefore contains a perfect record of the sound, far more delicate than the indentations in the tin-foil of the mechanical phonograph. The probable construction of C would be a cotton, silk or other thread, among whose fibres would be spun (or otherwise mixed) hard steel dust, or short clippings of very fine steel wire, hardened. Each piece would, of course, become a complete magnet. Other forms of C might be a brass, lead or other wire or ribbon through which the steel dust was mixed in melting—being hardened afterwards in the case of brass or any metal with a high melting point.

Another imaginable form of C would be simply a hard steel wire, but it is scarcely possible that it would divide itself up properly into a number of short magnets. . If it could be made to work it would obviously be the simplest thing yet suggested.”

The publication of Oberlin Smith’s idea was truly groundbreaking in terms of technological developments in magnetic recording. Many engineers were inspired by this article and set about trying to develop magnetic recording devices.

In 1898, 10 years after Smith published his idea, Danish telephone engineer Valdemar Poulsen invented the world’s first magnetic recorder, using steel wire as a recording medium.

This device, shown in Fig. 3.2, is very similar in structure to Edison’s phonograph, except that the cylinder is wrapped in steel wire rather than tin foil or wax and it has a electromagnet touching the wire.

This magnet plays the same role as the needle used in the phonograph. As the cylinder revolves, the magnet runs along the wire, using continuous magnetisation to record sound on it.

To play back the sound, the magnetised wire is run through the same electromagnet, allowing the recording to be reproduced as an electrical current induced in the coil through magnetisation. Poulsen called this instrument the “Telegraphone”.

As a telephone engineer, he apparently intended to record voices transmitted by telephone (an answerphone, so to speak). Poulsen gained patent rights for the telegraphone in Denmark, the United States, the United Kingdom, France and other key countries and embarked on a major marketing campaign for it.

Although the telegraphone had promising prospects with a well-received exhibit at the Exposition Universelle in 1900 in Paris, it failed as a business venture, as the products were fraught with problems: the quality was not good enough, they were prone to breaking down, and it was diffcult to achieve the desired sound quality.

The improved development and performance of the disc recorders and the popularity of the record industry boosted the dominance of the gramophone and the magnetic wire recorder was largely forgotten by the public. Poulsen and his assistants worked hard to improve the performance of magnetic recording and achieved some results that would later become relevant, such as the invention of DC bias.

While the telegraphone business venture failed to take off, Poulsen and his assistant Peder O. Pedersen worked hard to improve the telegraphone. In 1907, they acquired patent rights in the United States for their DC bias system.

The DC bias technology was very effective in improving sound quality by increasing the sensitivity of the recording and reducing distortion.

It became an essential piece of technology for magnetic recording in devices such as the wire recorder for the next 30 years until AC bias was invented.

When a magnetic field is externally applied to a magnetic substance and gradually strengthened, the internal magnetic flux of the magnetic substance also increases; however, it only increases to a certain extent. The magnetic fux at this point is called the maximum magnetic flux density (Bm).

If the external magnetic field is reduced to 0 at this point, the magnetic substance retains its internal magnetic flux density rather than also returning to 0. This means that the magnetic substance has become a magnet (it has become magnetised).

This magnetic flux density is called residual magnetic flux density (Br); the substance will never become a stronger permanent magnet than it is at this point. The north pole of a magnet created through magnetisation in one direction would have become the south pole of the magnet if the magnetisation were to have taken place in the opposite direction.

The magnetic field forms a symmetrical curve corresponding to the strength of the magnet, as shown in Fig. 3.4. This curve is called the magnetisation curve or hysteresis curve.

When a completely non-magnetised material is magnetised, the magnetization follows the 0-a, 0-c curve shown in Fig. 3.4.

In the initial stage, this curve is called the initial magnetisation curve. In a magnetic recorder, the horizontal axis corresponds to the recording magnetic field applied to the magnetic material (wire, later magnetic tape) by
the head, while the vertical axis shows the intensity of the magnetisation.

The magnetic field produced by the head is in proportion to the strength of the recording signal, that is, the recording current flowing through the head. Since the initial magnetisation curve is not a straight line, the result of magnetisation will be a distorted waveform even if a magnetic field is applied according to the sound being recorded.

This is called unbiased recording, shown in Fig. 3.5. Signifcant distortion occurs where a recording is made where the magnetisation curve is not in a straight line. Having the recording current as DC and using a near-straight magnetisation curve reduces distortion and produces better sound quality. This is called DC bias recording.

While using straight-line section a of the magnetisation curve shown in Fig. 3.6 reduces distortion, as shown in Fig. 3.7, if we look at the overall magnetisation curve, we see that section b on the outer loop is a longer straight-line section, so it would be better to use section b.

First, a magnetic substance is applied to a saturation feld to create Br; the substance is then biased in one direction without reducing the magnetic fux density; the recording current is then added and DC bias recording can be achieved using section b, as shown in Fig. 3.8. This was the DC bias method invented by Poulsen and Pedersen, achieving good recording quality by using long straight sections of the magnetic curve.

Poulsen continued working hard to promote the wire recorder, setting up a sales company in the United States in the hope of popularising it. He also continued to make improvements to the telegraphone itself, but he was never able to dominate the market because the device was lacking both in terms of competitive pricing and in the degree of technical perfection required for ease of use and good performance. The wire recorder failed as the popular choice of sound recorder due to the growth and development of the disc gramophone.

However, by the late 1920s there was a growing interest in magnetic recorders in felds such as broadcasting and military
communications and further research began to be carried out, especially in the West.

One feature of the wire recorder was that it could play continuously for longer periods than records; there was a demand in these felds for such a feature. These recorders were actually implemented in some areas in Europe, such as the large, steel ribbon recorders used in broadcasting, which replaced the steel wire with steel foil as the recording medium.

Fig. 3.9 shows an improved telegraphone from around 1920. This is an archetypal tape recorder, with the wire-wound reel driven by a motor and use of the left and right reels alternating when the recorded wire is rewound.

Fig. 3.10 shows a British Marconi-Stille steel ribbon recorder used for broadcasting by the BBC. This huge device weighed one tonne and could record for 30 minutes on a steel ribbon that was 3mm wide, 80µm thick and 3,000m long. One of these was imported by Japan in 1937 and used for foreign-language broadcasting by NHK Tokyo.

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The wire recorders and steel ribbon recorders were certainly not easy to use. They used solid metal recording media; if the wire came unwound it was extremely difficult to put it back; if it broke, it had to be welded (geschweisst oder gelötet) back together.

It is not difficult to imagine that the question was often posed of whether a more suitable material could be used as a recording medium for a magnetic recorder that was easier to use and could overcome these drawbacks.

Although the idea to coat a tape of soft material with a powdered magnetic substance was proposed by A. Nasavischwily in Germany and Joseph A. O’Neill in the United States in the 1920s, but nobody had managed to build a working machine.

In 1928, German engineer Fritz Pfeumer (Anmerkung : Er war nach wie vor Österreicher und lebte in Leipzig) coated paper tape with iron oxide to create a “recording tape” and made the world’s frst tape recorder, called the “Sound Paper Machine”.

While this machine had all the basic elements of a tape recorder and could be hailed as the world’s frst tape recorder, it crucially lacked in performance and could not produce a satisfactory quality of sound.

The coated magnetic tape did not have an even surface and the coating was not very well attached; during playback the magnetic particles would scatter on coming into contact with the head. Due to this, it became known as the “Sandpaper Machine”.

Pfleumer was granted patent rights in 1930 and took the world’s first tape recorder to all of the major electrical manufacturers in Germany to try to market it, but could not raise much interest because despite the potential of the technology, it lacked in performance.

However, in 1932, the president of Allgemeine Elektricitäts-Gesellschaft (AEG) showed some interest, buying the patent rights from Pfleumer. AEG immediately set up a research laboratory on magnetic recording and set about improving the Sound Paper Machine and the magnetic tape.

Being an electrical manufacturer, AEG needed experts in chemistry to improve the magnetic tape and sought assistance from IG Farben. Consequently, the IG Farben’s Ludwigshafen factory (later BASF) ended up collaborating on the magnetic tape project.

While IG Farben worked on developing the tape, AEG put its efforts into research and development of the magnetic recorder, completing the forerunner to the modern tape recorder – the “Magnetophon” – in 1934 (Fig. 3.12).

AEG planned to exhibit it at a radio show that year, but several defects were discovered in the drive train and the amplifer right before the show, so the exhibit was withdrawn.

AEG made further improvements to the drive mechanism and other parts and enclosed the mechanism unit, the amplifer unit and the speaker unit in separate housings.

The combined system went on display at the Berlin Radio Show in 1935 as the “K1 Magnetophon”. The world’s first practical tape recorder and magnetic tape was successfully demonstrated in public. As well as having high-quality tape developed by a specialised manufacturer, it had a stable tape drive system and ring heads that would not put excess pressure on the tape and damage it. These developments meant that the Magnetophon had most of the elements of a modern tape recorder.
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AEG developed a range of other models after the K1 Magnetophon, such as a console model and a portable model. These began to be used for monitoring radio broadcasts and recording military and police interrogations.

While broadcasting offices mainly used disc recorders, most of the broadcasting offices in Germany had Magnetophons installed by the outbreak of the Second World War in 1939.

The adoption of AC bias in 1942 (it was 1941) made a major improvement to the sound quality, which had previously not been as good as the disc recorders. High-quality, pre-recorded broadcasts began to be transmitted all across Europe.

The Allied Forces, thinking that such a high quality broadcast could only be live (Anmerkung : und das über Mittelwelle !!), were mystified at how these shows could be broadcast continuously over the whole long night (Fig. 3.13).

Although the Magnetophon gained popularity in Germany as a new, high-quality recorder, all international technology exchange stopped at this time, as the machine with its broadcasting and recording uses would be particularly helpful to the military.

• Anmerkung : Das stimmt so nicht, denn die Magnetophon Vorführung im UFA Palast am Zoo in 1941 war "public" - und das vor mehr als 2000 geladenen Gästen.

The main sound recorders in the West at the time were the disc recorders; while there were some steel wire/ribbon recorders in use, they were not really practical recording machines.

Magnetophon technology was clearly superior for recording sound. The Second World War ended in late 1945 with an Allied victory. Magnetophon technology was analysed by the Allies, leading to the development of highly effcient tape recorders in the United States.
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