For many decades, magnetic tape has been an important medium for recording and retrieving audio, video and computer data. With technological advances in recording and storage, new types of storage media are replacing magnetic tape-based products, such as flash drives and hard discs for saving computer data, optical CDs to replace cassette and reel-to-reel tape for audio, and DVDs to replace VHS and Betamax video tapes. Magnetic tapes can be archived for many years if they are kept clean from debris, placed in an environment with proper temperature and humidity, and most importantly, kept away from magnets and magnetic fields.
The Process Of Magnetic Tape Recording
Particles on a magnetic tape are magnetized and oriented as they pass by a fluctuating magnetic field produced by a recording head. This magnetic field changes in response to the audio or video information, creating a representation of the material on tape. To retrieve the information stored on tape, the tape is pulled past a playback head, where the magnetized particles create a magnetic field read by the head.
Sources of Magnets and Magnetic Fields
All magnetic tape, whether it's in the form of a music cassette, reel-to-reel, DAT, VHS or other form, must be kept away from magnets and magnetic fields. Sources of magnets include speakers and refrigerator magnets, including business cards and other advertising materials that have flexible magnetic backings (for posting on refrigerator doors). Sources for electromagnetic fields include motors, transformers (including florescent light ballasts), television sets and electrical machinery. The information on magnetic tape has even been destroyed by airport detectors that scan luggage.
A Magnetic Field's Detrimental Effects On Tape
Exposure to magnetic fields must be avoided to prevent a deterioration of the quality, or even the total loss, of the information on a magnetic tape. In the case of computer data stored on tape, any reduction in the strength of the recorded material can render the data unreadable. A strong magnetic field will totally erase everything on a tape. Audio tapes will be silent when played, with only a residual, inherent audible white noise hiss, sound, and video tapes will only show snow on the screen. If tape is exposed to a weak magnetic field, an audio tape may suffer a slight loss in volume or a reduction of the high frequency component of music.
Magnetized Tape Heads
Magnetic tape comes in direct, close contact with audio and video recording and playback heads, and over time these heads can become magnetized. This results in a loss of high frequencies, making the sound muffled and not bright. Handheld head demagnetizers are available to demagnetize both audio and video tape heads, which should be done periodically.
Print Through
Since the particles on a magnetic tape are actually magnetized, they produce a tiny magnetic field. As the layers of tape are wound over top of each other and stored on a reel, particles on one layer can eventually magnetize the underlaying particles on the adjacent layer if enough time passes. This effect is called print through and can be more pronounced with tape that has a thin backing or binder. Print through is most noticeable in quiet passages of music where the music from another layer has been imprinted on the tape.
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