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Magnetic Tape

From Wikipedia, Chace Audio

Magnetic tape is a strand of thin, pliable polyester coated with magnetic iron oxide. Magnetic tape can reside on an open reel or in a contained cassette, and can store analog or digital information. Nearly all recording tape is of this type, whether used for recording audio, video or used for computer data storage.

A bunch of technical info:
Magnetic tape recording involves the use of a magnetizable medium moving with a constant speed past a recording head. An electrical signal analogous to audible sound waves is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head then picks up the changes in magnetic field from the tape and converts it back into an electrical signal.

Standard tape speeds vary by factors of two. Typical speeds were initially 15ips (inches per second), yielding 30 minutes of recording time on 10.5" reels with a capacity of 2400ft. 30ips speed was used for the highest quality work. 7 1/2ips was used for home audiophile pre-recorded tape, some high end home recording, and professional protection copies. 3 3/4ips was standard for home recording. 1 7/8ips and even 15/16ips was used for voice recording when audio quality wasn't an issue and long recording times were needed – for logging police and fire department calls, long meetings, etc. Tape speed factors are the same regardless of tape size: 1/4", 1/2", 1", 2", cassette, microcassette or tape cartridge.

At 15ips, magnetic tape has a frequency response of 20Hz to 20kHz depending on the quality of the recording equipment being used. Digital tape reproduces almost perfectly flat from 20Hz to 20kHz, whereas analog tape response is not uniformly flat. Analog frequency response will also decline at slower tape speeds such as 7 1/2ips & 3 3/4ips. Additionally, analog tape will require Dolby® NR whereas digital tape will not.

Stored properly, magnetic tape can last over 50 years. 3M brands from the 50s and 60s seem to have the best shelf life in general – earlier Ampex brands were also fairly stable. In the early 1990s however, formulas were changed to be more ecologically friendly, and shelf life for magnetic tape became compromised. The main issue was that the tape emulsion became soft and gummy, causing the tape to drag on the tape heads, inducing wow, and quite often dragging it to a stop. Ampex 456, Quantegy 499, and especially BASF tape made from the early 90s on are all susceptible to this problem.

And now a little history curiously involving Nazis, Bing Crosby, and the Beatles:
Originally developed in 1930s Germany, magnetic tape revolutionized the broadcast and recording industries. In an age when all radio and later television was live, it allowed programming to be prerecorded. In a time when gramophone records had to be recorded in just one take, it allowed recordings to be created in multiple takes and easily mixed and edited with minimal loss in quality between generations. It was also one of the key enabling technologies in the development of modern computers, allowing massive amounts of data to be stored for long periods and rapidly accessed when needed.

During WWII, the allies became aware of radio broadcasts from Germany that were obviously transcriptions, but with audio quality which was indistinguishable from that of a live broadcast and whose duration was far longer than was possible from 78rpm discs. At the end of the war, the Allied capture of a number of German Magnetophon recorders from Radio Luxembourg aroused great interest stateside. These recorders had all the key technological features of analog magnetic recording, particularly the use of high-frequency bias.

Crooner Bing Crosby was a key player in the commercial development of magnetic tape. Crosby was stunned by its amazing sound quality and instantly recognized the commercial potential of the technology. At the time, live music was standard for radio broadcasts, but Crosby hated the regimentation of live shows, preferring the relaxed atmosphere of the recording studio. However, no major radio station at the time would allow broadcast of prerecorded transcription discs due to their relatively poor quality. Magnetic tape allowed Crosby to prerecord his radio show with a sound quality equal to a live performance, and the tape recordings could be played back many times without appreciable loss in quality. His shows were edited for better pacing and flow by tape splicing – also a first. 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.

Les Paul, who was a friend of Bing Crosby and a regular guest on his shows, had already been experimenting with overdubbed disc recordings when he received an early Ampex model. He modified it by adding additional record and play heads, thereby creating the world’s first practical tape-based multi-track recording system. The typical Ampex professional recorder of the early 1950s offered one or two tracks on 1/4" wide tape. The line soon expanded into three- and four-track machines using 1/2" tape. Ampex built a handful of machines in the late 1950s that could record as many as eight tracks on 1" tape, though four-track machines were considered state-of-the-art until about 1967.

The demand for more tracks suddenly exploded when musicians heard about the extensive overdubbing done on four-track machines for the Beatles’ album Sgt. Pepper's Lonely Hearts Club Band. In 1967, Ampex and 3M stepped up production of their eight-track machines. The Beatles’ White Album was recorded with this eight-track technology as was the Beach Boys Pet Sounds.

In 1968, Ampex introduced the world’s first 16-track professional recorder. It used a 2" tape transport design adapted from the video recording division. It quickly became legendary for its flexibility, reliability, and sound quality and ushered in the golden age of analog multi-track recording lasting into the early 1990s. Later machines could record up to 24 tracks, and with the use of SMPTE time code, multiple machines could be linked together creating even more track possibilities as was used in Queen’s Bohemian Rhapsody.

As digital recording technology has boomed due to its lower cost and flexibility, the use of tape-based recording has diminished.

This article is licensed under the GNU Free Documentation License found at http://www.gnu.org/copyleft/fdl.html. It uses material from the Wikipedia article at http://en.wikipedia.org/wiki/Magnetic_tape.

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