Magnetic wire recording Wire recording or magnetic wire recording is an analog type of audio storage in which a magnetic recording is made on thin steel or stainless steel wire. The wire is pulled rapidly across a recording head, which magnetizes each point along the wire in accordance with the intensity and polarity of the electrical audio signal being supplied to the recording head at that instant. By later drawing the wire across the same or a similar head while the head is not being supplied with an electrical signal, the varying magnetic field presented by the passing wire induces a similarly varying electric current in the head, recreating the original signal at a reduced level. Magnetic wire recording was replaced by magnetic tape recording, but devices employing one or the other of these media had been more or less simultaneously under development for many years before either came into widespread use. The principles and electronics involved are nearly identical. Wire recording initially had the advantage that the recording medium itself was already fully developed, while tape recording was held back by the need to improve the materials and methods used to manufacture the tape. Magnetic recording was demonstrated in principle as early as 1898 by
Valdemar Poulsen in his
telegraphone. Magnetic wire recording, and its successor,
magnetic tape recording, involve the use of a magnetized medium that moves with a constant speed past a
recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head can then pick up the changes in the magnetic field from the tape and convert them into an electrical signal. With the addition of electronic amplification developed by Curt Stille in the 1920s, the telegraphone evolved into
wire recorders, which were popular for voice recording and
dictation during the 1940s and into the 1950s. The reproduction quality of wire recorders was significantly lower than that achievable with phonograph disk recording technology. There were also practical difficulties, such as the tendency of the wire to become tangled or snarled. Splicing could be performed by knotting together the cut wire ends, but the results were not very satisfactory. On Christmas Day, 1932, the
British Broadcasting Corporation first used a steel tape recorder for their broadcasts. The device used was a Marconi-Stille recorder, a huge and dangerous machine which used steel tape that had sharp edges. The tape was wide and thick running at past the recording and reproducing heads. This meant that the length of tape required for a half-hour program was nearly and a full reel weighed .
Magnetic tape sound recording In Germany, engineers at
AEG, working with the chemical giant
IG Farben, created the world's first practical magnetic tape recorder, the 'K1', which was first demonstrated in 1935. During
World War II, an engineer at the
Reichs-Rundfunk-Gesellschaft discovered the
AC biasing technique. With this technique, an inaudible high-frequency signal, typically in the range of 50 to 150 kHz, is added to the audio signal before being applied to the recording head. Biasing radically improved the sound quality of magnetic tape recordings. By 1943, AEG had developed stereo tape recorders. During the war, the
Allies became aware of radio broadcasts that seemed to be transcriptions (much of this due to the work of
Richard H. Ranger), but their audio quality was indistinguishable from that of a live broadcast and their duration was far longer than was possible with 78 rpm discs. At the end of the war, the Allies captured a number of German
Magnetophon recorders from Radio Luxembourg which aroused great interest. These recorders incorporated all of the key technological features of analog magnetic recording, particularly the use of high-frequency bias. American audio engineer
John T. Mullin served in the U.S. Army Signal Corps and was posted to Paris in the final months of World War II. His unit was assigned to find out everything they could about German radio and electronics, including the investigation of claims that the Germans had been experimenting with high-energy directed radio beams as a means of disabling the electrical systems of aircraft. Mullin's unit soon amassed a collection of hundreds of low-quality magnetic dictating machines, but it was a chance visit to a studio at
Bad Neuheim near
Frankfurt while investigating radio beam rumors that yielded the real prize. Mullin was given two suitcase-sized AEG 'Magnetophon' high-fidelity recorders and fifty reels of recording tape. He had them shipped home and over the next two years, he worked on the machines constantly, modifying them and improving their performance. His major aim was to interest Hollywood studios in using magnetic tape for movie soundtrack recording. Mullin gave two public demonstrations of his machines, and they caused a sensation among American audio professionals—many listeners could not believe that what they were hearing was not a live performance. By luck, Mullin's second demonstration was held at
MGM studios in
Hollywood and in the audience that day was
Bing Crosby's technical director, Murdo Mackenzie. He arranged for Mullin to meet Crosby, and in June 1947, he gave Crosby a private demonstration of his magnetic tape recorders. Crosby was stunned by the amazing sound quality and instantly saw the huge commercial potential of the new machines. Live music was the standard for American radio at the time and the major
radio networks did not permit the use of disc recording in many programs because of their comparatively poor sound quality. But Crosby disliked the regimentation of live broadcasts, preferring the relaxed atmosphere of the
recording studio. He had asked
NBC to let him pre-record his 1944–45 series on
transcription discs, but the network refused, so Crosby had withdrawn from live radio for a year, returning for the 1946–47 season only reluctantly. Mullin's tape recorder came along at precisely the right moment. Crosby realized that the new technology would enable him to pre-record his radio show with a sound quality that equaled live broadcasts and that these tapes could be replayed many times with no appreciable loss of quality. Mullin was asked to tape one show as a test and was immediately hired as Crosby's chief engineer to pre-record the rest of the series. Crosby became the first major American music star to use tape to pre-record radio broadcasts and the first to master commercial recordings on tape. The taped Crosby radio shows were painstakingly edited through tape-splicing to give them a pace and flow that was wholly unprecedented in radio. Mullin even claims to have been the first to use
canned laughter; at the insistence of Crosby's head writer, Bill Morrow, he inserted a segment of raucous laughter from an earlier show into a joke in a later show that had not worked well. Keen to make use of the new recorders as soon as possible, Crosby invested $50,000 of his own money into
Ampex, and the tiny six-man concern soon became the world leader in the development of tape recording, revolutionizing radio and recording with its famous Ampex Model 200 tape deck, issued in 1948 and developed directly from Mullin's modified Magnetophones. Development of magnetic tape recorders in the late 1940s and early 1950s is associated with the
Brush Development Company and its licensee,
Ampex; the equally important development of magnetic tape media itself was led by
Minnesota Mining and Manufacturing corporation (now known as 3M).
Multitrack recording The next major development in the magnetic tape was
multitrack recording, in which the tape is divided into multiple tracks parallel with each other. Because they are carried on the same medium, the tracks stay in perfect synchronization. The first development in multitracking was
stereo sound, which divided the recording head into two tracks. First developed by German audio engineers ca. 1943, two-track recording was rapidly adopted for modern music in the 1950s because it enabled signals from two or more microphones to be recorded separately at the same time (while the use of several microphones to record on the same track had been common since the emergence of the
electrical era in the 1920s), enabling stereophonic recordings to be made and edited conveniently. (The first stereo recordings, on disks, had been made in the 1930s, but were never issued commercially.) Stereo (either true, two-microphone stereo or multi mixed) quickly became the norm for commercial classical recordings and radio broadcasts, although many
pop music and
jazz recordings continued to be issued in
monophonic sound until the mid-1960s. Much of the credit for the development of multitrack recording goes to guitarist, composer and technician
Les Paul, who also helped design the famous
electric guitar that
bears his name. His experiments with tapes and recorders in the early 1950s led him to order the first custom-built eight-track recorder from Ampex, and his pioneering recordings with his then-wife, singer
Mary Ford, were the first to make use of the technique of multitracking to record separate elements of a musical piece asynchronously — that is, separate elements could be recorded at different times. Paul's technique enabled him to listen to the tracks he had already taped and record new parts in time alongside them. Multitrack recording was immediately taken up in a limited way by Ampex, who soon produced a commercial 3-track recorder. These proved extremely useful for popular music since they enabled backing music to be recorded on two tracks (either to allow the overdubbing of separate parts or to create a full stereo backing track) while the third track was reserved for the lead vocalist. Three-track recorders remained in widespread commercial use until the mid-1960s and many famous pop recordings — including many of
Phil Spector's so-called
Wall of Sound productions and early
Motown hits — were taped on Ampex 3-track recorders. Engineer
Tom Dowd was among the first to use the multitrack recording for popular music production while working for
Atlantic Records during the 1950s. The next important development was 4-track recording. The advent of this improved system gave recording engineers and musicians vastly greater flexibility for recording and overdubbing, and 4-track was the studio standard for most of the later 1960s. Many of the most famous recordings by
The Beatles and
The Rolling Stones were recorded on 4-track, and the engineers at London's
Abbey Road Studios became particularly adept at a technique called
reduction mixes in the UK and
bouncing down in the United States, in which several tracks were recorded onto one 4-track machine and then mixed together and transferred (bounced down) to one track of a second 4-track machine. In this way, it was possible to record dozens of separate tracks and combine them into finished recordings of great complexity. All of the Beatles' classic mid-1960s recordings, including the albums
Revolver and ''
Sgt. Pepper's Lonely Hearts Club Band'', were recorded in this way. There were limitations, however, because of the build-up of noise during the bouncing-down process, and the Abbey Road engineers are still famed for their ability to create dense multitrack recordings while keeping background noise to a minimum. 4-track tape also enabled the development of
quadraphonic sound, in which each of the four tracks was used to simulate a complete 360-degree surround sound. A number of albums were released both in stereo and quadraphonic format in the 1970s, but 'quad' failed to gain wide commercial acceptance. Although it is now considered a gimmick, it was the direct precursor of the surround sound technology that has become standard in many modern
home theatre systems. In a professional setting today, such as a studio,
audio engineers may use 24 tracks or more for their recordings, using one or more tracks for each instrument played. The combination of the ability to edit via tape splicing and the ability to record multiple tracks revolutionized studio recording. It became common studio recording practice to record on multiple tracks and bounce down afterward. The convenience of tape editing and multitrack recording led to the rapid adoption of magnetic tape as the primary technology for commercial musical recordings. Although rpm and 45 rpm
vinyl records were the dominant consumer format, recordings were customarily made first on tape, then transferred to disc, with Bing Crosby leading the way in the adoption of this method in the United States.
Further developments Analog magnetic tape recording introduces noise, usually called
tape hiss, caused by the finite size of the magnetic particles in the tape. There is a direct tradeoff between noise and economics.
Signal-to-noise ratio is increased at higher speeds and with wider tracks, and decreased at lower speeds and with narrower tracks. By the late 1960s, disk reproducing equipment became so good that audiophiles soon became aware that some of the noise audible on recordings was not surface noise or deficiencies in their equipment, but reproduced tape hiss. A few specialist companies started making
direct to disc recordings, made by feeding microphone signals directly to a disk cutter (after amplification and mixing), in essence, reverting to the pre-War direct method of recording. These recordings never became popular, but they dramatically demonstrated the magnitude and importance of the tape hiss problem. Before 1963, when
Philips introduced the
Compact audio cassette, almost all tape recording had used the
reel-to-reel format. Previous attempts to package the tape in a convenient cassette that required no threading met with limited success; the most successful was
8-track cartridge used primarily in automobiles for playback only. The Philips Compact audio cassette added much-needed convenience to the tape recording format and, a decade or so later, had begun to dominate the consumer market, although it was to remain lower in quality than open-reel formats. In the 1970s, advances in solid-state electronics made the design and marketing of more sophisticated analog circuitry economically feasible. This led to a number of attempts to reduce tape hiss through the use of various forms of volume compression and expansion, the most notable and commercially successful being several systems developed by
Dolby Laboratories. These systems divided the frequency spectrum into several bands and applied volume
compression/expansion independently to each band (Engineers now often use the term
compansion to refer to this process). The Dolby systems were very successful at increasing the effective dynamic range and signal-to-noise ratio of analog audio recording; to all intents and purposes, audible tape hiss could be eliminated. The original
Dolby A was only used in professional recording. Successors found use in both professional and consumer formats;
Dolby B became almost universal for prerecorded music on cassette. Subsequent forms, including
Dolby C, (and the short-lived
Dolby S) were developed for home use. In the 1980s,
digital recording methods were introduced, and analog tape recording was gradually displaced, although it has not disappeared by any means. (Many professional studios, particularly those catering to big-budget clients, use analog recorders for multitracking and/or mixdown.) The digital audio tape never became important as a consumer recording medium, partially due to legal complications arising from
piracy fears on the part of the record companies. They had opposed magnetic tape recording when it first became available to consumers, but the technical difficulty of juggling recording levels, overload distortion, and residual tape hiss was sufficiently high that unlicensed reproduction of magnetic tape never became an insurmountable commercial problem. With digital methods, copies of recordings could be exact, and copyright infringement might have become a serious commercial problem. Digital tape is still used in professional situations and the
DAT variant has found a home in computer data backup applications. Many professional and home recordists now use hard-disk-based systems for recording, burning the final mixes to
recordable CDs. Most Police forces in the United Kingdom (and possibly elsewhere) still use analog compact cassette systems to record Police Interviews, as they provide a medium less prone to accusations of tampering. ==Recording on film==