Magnetic Recording | Research & Encyclopedia Articles

Magnetic Recording

Magnetic recording is the technique of storing electric signals as a magnetic pattern on a moving magnetic surface. The concept of recording sound on magnetic tape--and thus the principle of the tape recorder--was worked out theoretically in an 1888 article by the English inventor Oberlin Smith (1840-1926). The article, entitled "Several Possible Developments of the Phonograph," proposed using fabric strips containing iron filings as "tapes." It was, however, 10 years later that Smith's ideas were adapted and the first working magnetic tape recorder was introduced. In 1898, 20-year-old Danish inventor and physicist Valdemar Poulsen created a device that recorded and reproduced sounds by residual magnetization of a steel wire. The telegraphone, as it was called, was demonstrated at the 1900 World Fair in Paris, but the world took little notice of the new technology at the time. The invention of magnetic recording tape is variously attributed to J. A. O'Neill (b.1909), who is said to have created a paper version in 1927 in the United States, and the German engineer Fritz Pfleumer, who in 1928 developed a tape made by bonding a thin coating of oxide to strips of either paper or film. It was Pfleumer who filed the first audiotape patent in 1929. There is no doubt, however, that audiotape was an improvement over existing methods, such as records, for recording and storing sound. The tape was easier to use, store, and edit, and less expensive to produce. In 1935, the German electronics firm AEG produced a prototype of a record/playback machine, called a magnetophon, based on Pfleumer's idea, but using plastic tape. BASF went on to refine the tape AEG had used, presenting the first usable magnetic tape at the Berlin Fair in 1935. The first public tape recording was made by the London Philharmonic Orchestra at the BASF factory in Ludwigshafen, Germany, in 1936. Other recording devices were also being developed concurrently. In 1937 or 1938, Marvin Camras, a U.S. inventor, built a magnetic wire recorder, using a variation on the early work of Poulsen. His recorder used a revolutionary magnetic recording head to record around the wire symmetrically. Early versions of his recorders were used during World War II for training and strategic purposes, such as to simulate battle sounds at noninvasion locations and therefore mislead the enemy. Camras went on to develop his recording techniques for home use. He invented the first magnetic coatings that modern recording tape is based on; these coatings are used in videotape, computer tape, and floppy disks for personal computers. He also discovered high-frequency bias, used on almost all tape recorders today to improve sound quality, and developed multi-track tape recording, magnetic sound for motion pictures, videotape recorders, a variety of improved recording heads, and stereophonic sound reproduction.

Thin plastic tapes have become the medium universally used in tape recorders. The tapes have magnetic coatings consisting of magnetically active particles, most commonly iron oxide and chromium dioxide. Each of these particles, in effect, is a tiny permanent magnet embedded in the coating. As the tape passes around the five magnetic heads of the tape recorder, sound is recorded, replayed, or erased according to the heads that are activated. A recording head magnetizes the passing tape in such a way that the magnetic particles on it are realigned. The resulting magnetization pattern remains on the tape, which may be rewound and replayed as often as desired, until erased or changed. The audiocassette, introduced in 1963 by the Philips Company of the Netherlands, was made possible by Pfleumer's earlier development of audiotape. Audiotape was used in a reel-to-reel format, which was complicated and unwieldy, since the user had to thread tape through the machine and onto a take-up reel. Until the audiocassette format, sound recording technology had remained primarily a professional tool. Because of the ease and economy of the audio-cassette, magnetic recording tape recordings could compete with long playing (LP) records (LPs). The cassette was immediately popular because it made inserting, advancing, and rewinding a tape fast and easy; it could also be stopped and ejected at any point in the tape. The cassette housing protected the tape from wear and damage due to handling and thus reduced the loss of sound quality. Eight-track cartridges were another innovation in magnetic recording, although the audiocassette has proved more popular and long-lasting. Because the rather bulky 8-track used an endless-loop format, the tape could be played continuously, without being flipped over by the listener. But the invention of the microchip allowed audiotape players to be made smaller and more portable, and with the introduction of products such as Sony's compact Walkman, cassettes prevailed. Although the audiocassette is economical and still widely used, digital technologies are revolutionizing the industry by enabling the recording, storage, and playback of sound in new ways. Digital audio tape (DAT) recorders became widely available in the United States in 1990. A digital system, as opposed to a standard analog system, enables a home recorder to make a tape copy that is an exact replica--not just an approximation--of the original sounds on a cassette that is half the size of the typical audiocassette. Digital technology records sound in a code of binary numbers (a series of 0s and 1s), so each subsequent recording is simply a copy of the code. Analog recordings, on the other had, record sound as a wave pattern and, like using a copy of one key as a pattern for another, each generation of recordings is subject to increasing distortion.

Magnetic tape recording is not just an audio phenomenon. Video casettes record video through video cameras or on video casette recorders (VCR) in much the same way as analog audio casettes and tape recorders log sound. Standard videotapes are significantly larger than audio tapes, although the introduction of smaller casettes has allowed for the use of smaller video cameras. The video must be transferred to a standard-sized casette or placed in a standard-sized converter to be played in a VCR, however.