Magnetic tape recorder: Wikis

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A reel-to-reel tape recorder.

A tape recorder, tape deck, reel-to-reel tape deck, cassette deck or tape machine is an audio storage device that records and plays back sound, usually using magnetic tape, either wound on a reel or in a cassette, for storage. It records a fluctuating signal by moving the tape across a tape head that polarizes the magnetic domains in the tape in proportion to the audio signal.

Contents

History

An early experimental non-magnetic tape recorder patented in 1886 by Alexander Graham Bell's Volta Laboratory.

Likely the earliest known audio tape recorder was a non-magnetic, non-electric version invented by Alexander Graham Bell's Volta Laboratory and patented in 1886 (U.S. Patent 341,214).[1] It employed a 3/16-inch wide strip of wax-covered paper that was coated by dipping it in a solution of beeswax and paraffin and then had one side scraped clean, with the other side allowed to harden. The machine was built of sturdy wood and metal construction, and hand powered by means of a knob fastened to the flywheel. The wax strip passed from one eight-inch reel around the periphery of a pulley (with guide flanges) mounted above the V-pulleys on the main vertical shaft, where it came in contact with either its recording or playback stylus. The tape was then taken up on the other reel. The sharp recording stylus, actuated by a vibrating mica diaphragm, cut the wax from the strip. In playback mode, a dull, loosely mounted stylus, attached to a rubber diaphragm, carried the reproduced sounds through an ear tube to its listener.[1]

Both recording and reproducing heads, mounted alternately on the same two posts, could be adjusted vertically so that several recordings could be cut on the same 3/16-inch wide strip. While the machine was never developed commercially, it was an interesting ancestor to the modern magnetic tape recorder which it resembled somewhat in design. The tapes and machine created by Bell's Associates, examined at one of the Smithsonian Institution's museums, became brittle, and the heavy paper reels warped. The machine's playback head was also missing. Otherwise, with some reconditioning, they could be placed into working condition.[1]

Other 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. The first practical tape recorder was called K1 and demonstrated in Germany in 1935. Friedrich Matthias of IG Farben/BASF developed the recording tape, including the oxide, the binder, and the backing material. Development of magnetic tape recorders in the late 1940s and early 1950s is associated with Ampex; the equally important development of magnetic tape media itself was led by Minnesota Mining and Manufacturing Company (now known as 3M).

Further information: Further information: Magnetic tape sound recording –Early steel tape recorders

Description of operation

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Electrical

Electric current flowing in the coils of the tape head creates a fluctuating magnetic field. This causes the magnetic material on the tape, which is moving past and in contact with the head, to align in a manner proportional to the original signal. The signal can be reproduced by running the tape back across the tape head, where the reverse process occurs – the magnetic imprint on the tape induces a small current in the read head which approximates the original signal and is then amplified for playback. Many tape recorders are capable of recording and playing back at once by means of separate record and playback heads in line or combined in one unit.

Mechanical

Modern professional recorders usually use a three-motor scheme. One motor with a constant rotation speed provides traction for the capstan. This, usually combined with a rubber pinch roller, ensures that the tape speed does not fluctuate. Of the other two motors, one applies a very light torque to the supply reel, and the other a greater torque to the takeup reel, to maintain the tape's tension. During fast winding operation the pinch roller is disengaged and the reel motors provide the necessary power. The cheapest models use a single motor for all required functions, coupled to the capstan and reel spindles as needed with mechanical clutches and belts. There are also variants with two motors, in which one motor is used for rewinding only.

Later developments

A typical portable desktop cassette recorder from RadioShack.

Since their first introduction, analog tape recorders have experienced a long series of progressive developments resulting in increased sound quality, convenience, and versatility.

  • Two-track and, later, multi-track heads permitted discrete recording and playback of individual sound sources, such as two stereophonic channels, or different microphones during live recording. The more versatile machines could be switched to record on some tracks while playing back others, permitting additional tracks to be "laid down" to match previously recorded material such as a rhythm track.
  • Use of separate heads for recording vs. playback (three heads total, counting the erase head) enabled monitoring of the recorded signal a fraction of a second after recording. Mixing the playback signal back into the record input also created a primitive echo generator.
  • Dynamic range compression during recording and expansion during playback expanded the available dynamic range and improved the signal-to-noise ratio. dbx and Dolby Laboratories introduced add-on products in this area, originally for studio use, and later in versions for the consumer market. In particular, "Dolby B" noise reduction became very common in all but the least expensive cassette tape recorders.
    Solidyne GMS200 tape recorder with computer self-adjustment. Argentina 1980-1990
  • Computer controlled analog tape recorders were introduced by Oscar Bonello in Argentina.[2] The mechanical transport used three DC motors and introduced two new advances: automated microprocessor transport control and automatic adjustment of bias and frequency response. In 30 seconds the recorder adjusted its bias for minimum THD and best frequency response to match the brand and batch of magnetic tape used. The microprocessor control of transport allowed fast location of any point on the tape.

Limitations

The storage of an analogue signal on tape works well, but is not perfect. In particular, the granular nature of the magnetic material adds high-frequency noise to the signal, generally referred to as tape hiss. Also, the magnetic characteristics of tape are not linear. They exhibit a characteristic hysteresis curve, which causes unwanted distortion of the signal. Some of this distortion is overcome by using an inaudible high-frequency AC bias signal when recording, though the amount of bias needs careful adjustment for best results. Different tape material requires differing amounts of bias, which is why most recorders have a switch to select this (or, in a cassette recorder, switch automatically based on cutouts in the cassette shell). Additionally, systems such as Dolby B, Dolby C and Dolby HX-Pro have been devised to ameliorate some of the noise and distortion problems. Variations in tape speed cause flutter, which can be reduced by using dual capstans. Higher speeds used in professional recorders are prone to cause "head bumps," which are fluctuations in low-frequency response.

Variety of tape recorders

There is a wide variety of tape recorders in existence, from small hand-held devices to large multitrack machines. A machine with built-in speakers and audio power amplification to drive them is usually called a "tape recorder" or – if it has no record functionality – a "tape player," while one that requires external amplification for playback is usually called a "tape deck" (regardless of whether it can record).

Multitrack technology enabled the development of modern art music and one such artist, Brian Eno, described the tape recorder as "an automatic musical collage device".

Use of tape recorders

An important use of tape recorders is the recording of video. Video cassette recorders differ substantially from audio recorders due to the use of a rotating magnetic head that uses a helical scan over the tape medium. Helical scans increase the relative speed of the tape surface over the head.

While they are primarily used for sound recording, tape machines were also important for data storage before the advent of floppy disks and CDs, and are still used today, although primarily to provide an offline backup to hard disk drives.

Tapedeck speeds

There are many different tape speeds which are in use in all sorts of tape recorders. Most often these speeds appear on tapedecks. But – while meaning the same speed – many tapedecks are either in centimeters per second (cm/s) or in inches per second (in/s).

To overcome this, here is an overview:

cm/s in/s
1.2 15/32[3]
2.4 15/16
4.75 1 7/8
9.5 3 3/4
19 7 1/2
38 15
76 30
  • This article incorporates text from the United States National Museum Bulletin, a government publication in the public domain.

By providing a range of tape speeds, users can trade-off recording time against signal quality with higher tape speeds providing greater frequency response.

References

  1. ^ a b c Newville, Leslie J. Development of the Phonograph at Alexander Graham Bell's Volta Laboratory, United States National Museum Bulletin, United States National Museum and the Museum of History and Technology, Washington, D.C., 1959, No. 218, Paper 5, pp.69-79. Retrieved from ProjectGutenberg.org.
  2. ^ “A new tape transport system with digital control”, Oscar Bonello, Journal of Audio Engineering Society, Vol 31 # 12, December 1983
  3. ^ Martel Electronics. Terms commonly used for Tape Recorder. Tape Recorder Speed.

See also: tape formats

See also

External links


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