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Magnetic tape has been used for sound recording for more than 75 years. In this time, many advances in tape formulation, packaging, and audio fidelity have been made. Since some early refinements improved the fidelity, magnetic tape has been the highest quality analog sound recording medium available. As of 2007, magnetic tape is being replaced by digital systems for most sound recording purposes.

Magnetic wire recorders had successfully demonstrated the concept of magnetic recording prior to the development of magnetic tape, but they never offered audio quality comparable to the recording and broadcast standards of the time.

Contents 1 Origins 1.1 Magnetic recording 1.2 Early steel tape recorders 1.3 German developments 2 Commercialization 2.1 American developments 2.2 Bing Crosby's influence 2.3 Standardized products 3 Innovative uses 4 Magnetic tape speeds 5 See also 6 External links

Magnetic recording was conceived of as early as 1877 by Oberlin Smith and demonstrated in practice in 1898 by Valdemar Poulsen. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which 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 magnetic field from the tape and convert it into an electrical signal.

Early tape recorders were created by replacing the steel wire of a wire recorder with a thin steel tape. The first of these modified wire recorders was the Blattnerphone, created in 1929 or 1930 by the Ludwig Blattner Picture Corporation.

In 1931, Clarence N. Hickman of Bell Labs completed a prototype steel tape recorder based telephone answering machine. The machine saw limited use because AT&T policy forbade its use on public telephone lines.

On Christmas day 1932 the British Broadcasting Corporation first used a tape recorder for their broadcasts. The device used was a Marconi-Stille recorder, a huge tape machine which used steel razor tape 3 mm wide and 0.08 mm thick. In order to reproduce the higher audio frequencies it was necessary to run the tape at a 90 metres per minute past the recording and reproducing heads. This meant that the length of tape required for a half-hour programme was nearly 3 kilometres and a full reel weighed 25 kg. For safety reasons these machines would only be operated in a locked room by remote control. Due to the tape's speed, springiness and razor-like sharp edges, if the tape broke while in operation, it could unspool, fly off and potentially decapitate anything in its path. Besides this, the methods of recording could lead to massive data loss and poor audio quality because of its nature.

By the mid 1930s, the C. Lorenz Company in Germany, with the help of Semi Joseph Begun, had developed a steel tape recorder that was briefly popular with European telephone companies and German radio networks. In 1938, Begun left Germany and joined the Brush Development Company in the United States, where work continued but attracted little attention.

Magnetic tape recording as we know it today was developed in Germany during the 1930s at BASF (then part of the chemical giant IG Farben) and AEG.

Engineers at AEG created the world's first practical magnetic tape recorder, the 'K1', which was first demonstrated in 1935.

During World War II AEG engineers discovered the AC biasing technique. A high-frequency signal, typically in the range of 40 to 150 kHz, is added to the audio signal before being applied to the recording head. This means that the magnetization is performed at levels in the most linear portion of the medium's transfer function. Biasing radically improved sound quality and enabled them to develop their recorders to new heights of technical excellence; by 1943 they 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 Allied capture of a number of German Magnetophon recorders from Radio Luxembourg aroused great interest. These recorders incorporated all of the key technological features of analog magnetic recording, particularly the use of high-frequency "bias".

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).

American audio engineer John T. Mullin and entertainer Bing Crosby were key players in the commercial development of magnetic tape. Mullin served in the U.S. Army Signal Corps and was posted to Paris in the final months of WWII; 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 rumours, 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 literally 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 didn't 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 realised that the new technology would enable him to pre-record his radio show with a sound quality that equalled 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 hadn't 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, revolutionising radio and recording with its famous Model 200 tape deck, issued in 1948 and developed directly from Mullin's modified Magnetophones.

Working with Mullin, Ampex rapidly developed two-track stereo and then three-track recorders. Spurred on by Crosby's move into television in the early 1950s, Ampex had developed a working monochrome videotape recorder by 1956 and later a color recorder, both created to tape Crosby's TV shows.

The typical professional tape recorder of the early 1950s used ¼" wide tape on 10½" reels, with a capacity of 2400 feet (730 metres). Typical speeds were initially 15 in/s (38.1 cm/s) yielding 30 minutes' recording time on a 2400 ft (730 m) reel. 30 in/s (76.2 cm/s) was used for the highest quality work. Domestic and portable recorders used seven, five or even three inch reels (or spools) Early professional machines used single sided spools but double sided spools soon became popular (particularly for domestic use) Tape spools were usually made from transparent plastic but metal spools were also used

Standard tape speeds varied by factors of two — 15 and 30 in/s were used for professional audio recording; 7½ in/s (19 cm/s) for home audiophile prerecorded tapes; 7½ and 3¾ in/s (19 and 9.5 cm/s) for audiophile and consumer recordings (typically on 7 in or 18 cm reels). 1⅞; in/s (4.76 cm/s) and occasionally even 15/16 in/s (2.38 cm/s) were used for voice, dictation, and applications where very long recording times were needed, such as logging police and fire department calls.

Magnetic tape brought about sweeping changes in both radio and the recording industry. Sound could be recorded, erased and re-recorded on the same tape many times, sounds could be duplicated from tape to tape with only minor loss of quality, and recordings could now be very precisely edited by physically cutting the tape and rejoining it.

Within a few years of the introduction of the first commercial tape recorder, the Ampex 200 model, launched in 1948, American musician-inventor Les Paul had invented the first multitrack tape recorder, bringing about another technical revolution in the recording industry. Tape made possible the first sound recordings totally created by electronic means, opening the way for the bold sonic experiments of the Musique Concrète school and avant garde composers like Karlheinz Stockhausen, which in turn led to the innovative pop music recordings of artists such as Frank Zappa, The Beatles and The Beach Boys.

Tape enabled the radio industry for the first time to pre-record many sections of program content such as advertising, which formerly had to be presented live, and it also enabled the creation and duplication of complex, high-fidelity, long-duration recordings of entire programs. It also, for the first time, allowed broadcasters, regulators and other interested parties to undertake comprehensive logging of radio broadcasts. Innovations like multitracking and tape echo enabled radio programs and advertisements to be pre-produced to a level of complexity and sophistication that was previously unattainable and tape also led to significant changes to the pacing of program content, thanks to the introduction of the endless-loop tape cartridge.

In sound recording, magnetic tape speed is often quoted in inches per second (abbreviated ips) for historical reasons. Magnetic tape speeds are commonly an even fraction of 30 ips:

ips	Typical use
120 (304 cm/s)	Used by some analog instrumentation recorders and loop bin duplicators.
60 (152 cm/s)	Used by some analog instrumentation recorders, as well as loop bin duplicators.
45 (114 cm/s)	Used by 3M's first digital audio recorder in 1978.
30 (76 cm/s)	The highest professional speed.
15 (38 cm/s)	The most common professional and studio speed for reel to reel including multitrack.
71⁄2 (19 cm/s)	The lowest professional speed, used on some single-speed studio recorders including multitrack. The highest domestic speed. Used on older single speed domestic machines. The most common speed for pre-recorded reel to reel tapes.
33⁄4 (9.5 cm/s)	Used on later single speed domestic machines. The second most common speed for pre-recorded reel to reel tapes. The speed specified for the 8-track cartridge. Used by some consumer multitrack machines using compact cassettes.
17⁄8 (4.76 cm/s)	The standard speed for compact cassettes. The lowest common reel to reel speed. Used for reel to reel message tapes. Used for message logging and similar specialised applications.
15⁄16 (2.38 cm/s)	The standard speed for microcassettes (although specified as 2.4 cm/s, see below). Also used for some "talking books" on compact cassette for the blind & visually impaired, issued by the Library of Congress.
15⁄32 (1.19 cm/s)	The standard alternative recording speed for microcassettes.

Tape recording first became common enough for the issue of compatibility between tape deck manufacturers to become an issue in the 1950s. At this time the most common speeds for professional recording were 30 ips and 15 ips, and some machines already supported both speeds. As the tape speed was determined by the speed of a synchronous motor driving a capstan, one way of achieving this was to switch the poles of the motor to a different configuration, halving or doubling the speed.

This system was extended to domestic tape decks, and so slower speeds as they were adopted tended to be exactly half the previous slowest speed. Pre-recorded tapes were mostly 7¹⁄₂ ips, with a few at 3³⁄₄ ips. Message tapes transmitted by post and call logging tapes were commonly recorded at 1⁷⁄₈ ips or even ¹⁵⁄₁₆ ips. The most common reel to reel speed of 7¹⁄₂ ips is approximately 19 cm/s.

Another cause of incompatibility between tape decks was the lack of standardisation of track widths and the use of alternate (rather than adjacent) stereo tracks by many manufacturers (which limited compatibility with mono equipment).

When Philips introduced the compact audio cassette, they chose to specify the reel-to-reel standard of 1⁷⁄₈ ips (approximately 4.76 cm/s). Although with narrower and thinner tape. Higher speed machines using compact cassettes commonly use 3³⁄₄ ips.

Although the microcassette is specified to have a standard record speed of 2.4 cm/s and low speed of 1.2 cm/s, in the dictaphone application for which it was designed these speeds are in practice identical to ¹⁵⁄₁₆ ips and ¹⁵⁄₃₂ ips. Playback speed is not specified, and on many machines is continuously variable.

• History of sound recording#Magnetic recording - Magnetic tape in the context of the history of sound recording.
• Sound recording and reproduction#Magnetic tape - Magnetic tape in the context of the history of sound recording.
• Analog recording - Other analog recording methods
• Audio format - General list of audio recording formats, including magnetic tape.
• Audio tape length and thickness - Details of different audio tape formats.
• Tape recorder - Details regarding the workings of the recording machines.
• Reel-to-reel audio tape recording - Details of using old style recorders.
• Multitrack recording - Advanced usage of sophisticated tape recorders.
• Preservation of magnetic audiotape

• A timeline of developments in magnetic recording.
• A Selected History of Magnetic Recording
• Walter Weber's Technical Innovation at the Reichs-Rundfunk-Gesellschaft
• Timeline from U of San Diego's Archive
• History of Recording Technology (WayBack Machine)
• History of Magnetic Tape (WayBack Machine)
• Description of the recording process with diagrams. pg. 2, pg. 3, pg. 4, pg. 5.