Tape recorder
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This article deals mainly with analog tape recorders for audio applications; information on digital recording, recording of video signals, and recording of data can be found in other articles.
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 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.
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[edit] Description of operation
[edit] Electrical part
Current flowing in the coils of the electromagnet causes the magnetic material on the tape 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.
[edit] Mechanical part
Professional recorders usually use a simple three-motor scheme. One motor with a constant rotation speed provides traction for the leading wheel that is usually combined with a capstan and flywheel to ensure that the tape speed does not fluctuate. The other two motors apply constant torque to maintain the tape's tension or wind the tape quickly. Cheaper models use a single motor for all required functions. There are also variants with two motors, in which one motor is used for rewinding only.
[edit] 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 noise to the signal, which is usually heard 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 switch automatically). Additionally, systems such as Dolby B 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.
[edit] Variety of tape recorders
There are a wide variety of tape recorders in existence, from small hand-held devices to large multitrack machines. 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".
[edit] 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.
[edit] See also: tape formats
- 8 track tape
- Cassette deck
- Elcaset
- Compact audio cassette
- Reel-to-reel audio tape recording
- Wire recording
- Helical scan
- Digital audio tape
