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Mag Tape Audio

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.

(from History of sound recording)

Magnetic recording

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 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.

advances and problems with wire recorders

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 low, however — significantly lower than that achievable with phonograph disk recording technology. Wire recorders could not prevent the wire from undergoing axial twisting, and hence could not ensure that the wire was oriented the same way during recording and playback. When oriented the wrong way, high frequencies were reduced and the sound was muffled. The hysteresis of the steel material resulted in nonlinear transfer characteristics, manifesting as distortion. There were other 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.

Early tape recorders

Early tape recorders were first developed in Germany. 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!

German developments

Magnetic tape recording as we know it today was developed in Germany during the late 1930s by the C. Lorenz company and by AEG . In 1938, S. J. Begun left Germany and joined Brush Development Company in the United States, where work continued but attracted little attention.

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 AEG engineers discovered the AC biasing technique. A 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. 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, particular the use of high-frequency "bias".

American developments

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.

Bing crosby's influence

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.

Standardized products

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

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). 17⁄8; 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.

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(from Sound recording and reproduction)
The other major inventions of this period were magnetic tape and the tape recorder(Telegraphone). Paper-based tape was first used but was soon superseded by polyester and acetate backing due to dust drop and hiss. Acetate was more brittle than polyester and snapped easily. This technology, the basis for almost all commercial recording from the 1950s to the 1980s, was invented by German audio engineers in the 1930s, who also discovered the technique of AC biasing, which dramatically improved the frequency response of tape recordings. Tape recording was perfected just after the war by American audio engineer John T. Mullin, whose pioneering recorders were based on captured German recorders, and the Ampex company produced the first commercially available tape recorders in the late 1940s.

uses

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.

Energy vs. shape

	1 Dim		2 Dim
	Strand	Tape	Sheet	Disk	Cylinder	other
Mechanical	rope beads	paper tape	paper & ink punched cards	gramophone (& vinyl) records	edison phonograph	clay tablet & scribe
Magnetism	wire recording core rope	mag tape	mag swipe card	HDD Floppy	drum memory	core ring MRAM
Optics		ticker tape	photo paper laser printed paper	CD, DVD, etc		Hologram
Electronic						RAM flash mem
Chemical	DNA RNA