Storage of Magnetic Tape (Audio and Video) Recordings
Many valuable video and audio recordings are in jeopardy because of improper storage techniques. All high-density data storage media must be treated with tender, loving care if they are to reproduce their information faithfully in years to come.
Like other alternatives, magnetic audio tape is not perfect, but it can and will last for decades or perhaps longer if properly cared for. This article deals with the many factors necessary for long-term storage of magnetic audio and video tape.
Library of Natural Sounds
Cornell Lab. of Ornithology
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The physical construction of magnetic audio and visual tape consists of a plastic film, such as cellulose acetate, polystyrene, or more recently, polyester. The binder, a thin layer of a synthetic material, usually polyurethane, is coated on one side of the film. Added to this binder are the microscopically small magnetic particles that store the sound waves.
The polyurethane binder is hygroscopic (ability to attract or absorb moisture from the air) and will deteriorate if improperly stored. These guidelines are to help prevent the following problems from developing:
- Severe tape deformation.
- Magnetic oxide separation from the polyester backing.
- Breakdown of the binder material.
- Loss of lubricants embodied in the tape.
- Mold and mildew growth.
- Severe print-through patterns (both pre and post).
- Partial erasure or deformation of the recorded audio signals. The high frequency information is the most vulnerable.
Materials Tools Supplies
- Hold-down tape
- Metal tape storage cans or polyethylene-cardboard-foil-polyethylene laminate boxes or cardboard boxes lined with pH neutral paper.
- Store magnetic tapes in a climate-controlled area. Storage conditions must be uniform in both temperature and humidity. Storage temperatures should be maintained at 68ºF with a relative humidity between 38% – 42% (ideally 40%).
- The storage area should be free of dust and stray magnetic fields. Any stray magnetic field with a flux density of 5 gauss or greater should be considered a potential problem.
- Where possible, use only 1.5mil reel-to-reel tape, stored on either metal or plastic reels that offer the largest possible (3-4in) un-slotted hubs. If cassettes are to be stored, use the thicker C-60 stock. This tape is more robust than the thinner C-90 stock and should offer better long-term performance.
- Digital Audio Tapes (DAT) of the open-reel DASH or PD format or the r-DAT format should be stored in conditions similar to those outlined above in paragraphs one and two of “Basic Recommendations”. These formats are still too new to determine their ultimate longevity for archival purposes, however, following the above guidelines should prove beneficial as these tapes are subject to the same problems as their analog counterpart. A good long-term storage practice for digital recordings (not directly applicable to analog) is to do a digital to digital copy i.e., “clone” of one’s digital tapes every few years. This practice should help to minimize high error rates, and dropouts that are the by-products of digital tape deterioration. Unless detected early on, they can render the recorded material useless.
- Video tape also should be stored following the guidelines detailed above in paragraphs one and two.
- Prior to shelving tapes for storage, wind tapes using the play function of the recorder. This will provide a reduced but constant tension throughout the reel thereby creating a uniform tape pack. The recommended winding tension for 1.5mil polyester tape should be a constant torque of 3.75 ounces measured at the hub of a 10.5in reel. Storing tapes in this “tails-out” fashion will help prevent edge damage, print-through and deformation.
- Secure the loose end of the tape to the reel using a specifically designed hold-down tape. This tape is designed just for this application offering good long-term adhesive qualities while leaving little, if any, residue on the tape upon removal.
- Avoid touching the surface of the tape with your fingers, as skin oils can have a negative effect on the binder and oxide materials.
- Package reels in sealed metal cans or sealed boxes of a material such as a polyethylene-cardboard-foil-polyethylene laminate, chemically stable plastic, or cardboard boxes lined with pH neutral paper.
- Store tape boxes vertically on the shelves made of non-magnetizable material.
- Keep the recorder in good condition. Clean the machine daily, check tensions on a regular basis, and demagnetize the heads at least once for every 20 hours of running time.
Print-through is an analog tape phenomenon in which one hears an echo or ghost of a given signal either prior to, or immediately following the actual recording. To help minimize print-through use the following guidelines:
- Use only thick tape stocks; i.e., 1.5mil back-coated for open reel and C-60 for cassettes.
- Store at recommended temperatures.
- Ship in insulated containers to reduce temperature variations. This also applies to closed cars in hot conditions. An inexpensive polystyrene cooler will keep tapes at moderate temperatures when they must be left in an automobile or shipped.
- Fast rewind tapes prior to playing. It appears that the mechanical action of rapid rewinding or spooling of tape can reduce print-through (this can vary with the type of tape stock). By storing tapes “tails-out” a rapid rewind must occur each time a tape is to be used, thereby reducing the print-through effect.
- Follow the above steps to prepare an original tape for copying. If a tape exhibiting print-through is not “exercised” prior to duplication, the print-through problem may be transferred permanently.
To prevent accidental erasure either from self-erasing or being erased accidentally:
- Break out the record safety tab on the cassette.
- Disable the record circuit on reel-to-reel machines by using the record lock-out or safe mode.
- When demagnetizing the recorder, always remove recorded material from the area in which one is working. Another room is the safest bet.
Proper labeling of the storage box and actual tape is very important. The labels should include the following information:
- Recording speed (3.75, 7.5, 15 ips) and equalization standard used: NAB or AES (U.S.), CCIR or IEC (Europe) for reel-to-reel tapes, 70 (Type II, high) or 120 (Type I, normal) microsecond for cassettes).
- Track format (stereo, mono, 2-track, 4-track, etc.).
- Noise reduction systems used (if any).
- Recording equipment utilized.
- Date, time and recording location.
- Contents of recording.
Airport security and mail sorting X-ray machines, when in good working order, have no affect on magnetic tape. Motors, generators, and transformers are designed for efficiency, so their magnetic fields are contained internally. It is unrealistic to believe that such devices could affect a tape kept more than several inches from the surface of such a device. Television sets and loudspeakers have magnetic coils, but their fields are very small and concentrated. Also, these devices are generally housed within a cabinet which makes direct contact with the coils unlikely.
However, dynamic microphones and some headphones may have fields large enough to cause second-harmonic distortion on audio tape, so take precautions when packing gear for field work.
Be aware that many office devices such as typewriters, computers, fax machines, telephones and photocopiers. all produce magnetic fields to varying degrees. Try to keep recorded tapes away from these devices. If in doubt, play it safe or measure the device or area with a magnetometer.