Analog Videotape[edit | edit source]
History[edit | edit source]
In the early 1950s, with the successful introduction of audio recording on magnetic tape, several companies in the U.S. and England began work on developing a similar system for for recording video signals. At the time, the only viable means of recording a live television broadcast was via a kinescope: a specially modified 16mm or 35mm motion picture camera filmed the image from a monitor. Kinescopes tended to have lower picture quality than live broadcasts, and were especially cumbersome when used for "time-shifting"--recording programs during a live broadcast on the East Coast, for playback three hours later on the West Coast. Videotape would provide much higher image quality, would eliminate the delays caused by film processing, and would be re-usable.
The first successful videotape recorder was introduced by the Ampex Corporation in 1956. Using 2" wide reel-to-reel tape, the format became known as '2" quad,' and was the standard broadcast videotape format for more than two decades, seeing wide use in network and local broadcasting, government, and other professional applications.
Since that time, more than 70 videotape formats have been introduced, some widely adopted, others seeing only a handful of uses. The first successful non-broadcast format was 1/2" EIAJ, which went on the market in 1965. Videocassettes--plastic housings which contain two reels of tape, to be inserted into a playback deck--were introduced in 1970, with Sony's 3/4" U-matic format. Digital formats were developed during the 1980s and 1990s, and gradually supplanted analog formats for both professional and consumer applications.
Technical Details[edit | edit source]
Magnetic Recording and Playback[edit | edit source]
In magnetic recording a flexible tape coated with a pigment that contains iron oxide particles moves in front of an electromagnet. The magnetic field varies according to the strength of a video or audio signal. As the tape passes the head, the varying field affects the magnetic orientation of the iron oxide particles to reflect the strength or weakness of the signal. In playback, the tape passes a magnetic head which converts the varying magnetism of the tape back into a video or audio signal.
Tape Composition[edit | edit source]
Analog videotape usually consists of three layers.
The flexible base of videotape is made of polyester (polyethylene-terephtalate, PE or PET).
The binder is the coating which contains the magnetic oxide particles, and is applied to the based during manufacturing. The binder consists of polyester urethane compounds, in which the oxides are suspended. May different binder formulations have been used during the years, varying from format to format, manufacturer to manufacturer, and even batch to batch.
Many videotapes have a backcoat applied to the reverse side of the tape, to reduce friction and static electricity buildup, as well as to facilitate an even tape wind.
Types of Analog Tape Formats[edit | edit source]
- 1" Type B video tape (Robert Bosch GmbH)
- 1" Type C videotape (Ampex, Marconi and Sony)
- 2" Quadruplex videotape (Ampex)
- 2" Helical Scan Videotape (Rank Cintel)
- Betacam (Sony)
- Betacam SP (Sony)
- Betamax (Sony)
- S-VHS (JVC) (1987)
- W-VHS (JVC) (1994)
- U-matic 3/4" (Sony)
- VCR, VCR-LP, SVRVERA (BBC experimental format ca. 1958)
- VHS (JVC)
- VHS-C (JVC)
- Video 2000 (Philips)
- Video8 (Sony) (1986)
- Hi8 (Sony) (mid-1990s)
Conservation Practices[edit | edit source]
Storage Conditions[edit | edit source]
In optimal environmental conditions, new videotape should last about ten years. They can actually last up to thirty years, and in some remarkable cases, fifty years. Proper storage conditions will give you a window of time to document tapes properly and to preserve works that need immediate attention, while keeping the lower priority tapes stable. The best long-term storage temperature is approximately 50° F at 25% relative humidity, with little fluctuation. These conditions cannot always be met, of course, but in any case, tapes should be stored with attention to the following parameters:
- Store videotape on metal shelving in cool, dry, stable conditions.
- Store tapes upright, like books.
- The storage space should be free of dust and away from sunlight. Containers should be kept clean and dust-free.
- Make sure there is no acidic plastic or paper inside videotape containers; it could accelerate decomposition.
- File valuable paper materials found inside the case separately from the tape, but note their existence and location in the relevant catalog record.
- Record temperature and humidity levels monthly to make sure environmental conditions are not fluctuating over time.
- At the same time check your collection on a micro level—take care that the tape containers are free of debris and dust.
- Before putting a cassette on the shelf, disable the record tab to prevent accidental erasure in the future.
Tape Winds[edit | edit source]
How a tape is wound can contribute to its longevity.
The wind of the tape should be even and somewhat tight, as tape is least vulnerable to external damage in a smooth pack. You can achieve an even wind by shuttling the tape to the end or to the beginning at a steady rate, but be careful with damaged or deteriorated tapes. When in doubt, do not attempt playback!
Secure loose ends of open reels with acid-free paper tape since ends can fold over or deform.
For consumer formats, the tape should be stored on the take-up hub (the reel onto which the tape spools as it plays) and for non-consumer, archival formats, the tape should be stored on the supply hub, the reel from which the tape is being spooled as it plays.
Reformatting[edit | edit source]
The A/V Artifact Atlas has examples of technical issues and anomalies in audio and visual signals, particularly during preservation reformatting.
Conservation Products & Supplies[edit | edit source]
Equipment[edit | edit source]
Equipment obsolescence[edit | edit source]
One of the primary threats to analog videotape is format obsolescence. Since 1956, more than 60 different, non-compatible videotape formats have been introduced. Some were widely adopted, and therefore playback equipment was produced in quantity. For less-successful formats, only a small number of playback decks may have been produced. In both cases, however, when a format becomes obsolete, manufacturers quickly stop supporting maintenance of decks, supplies of parts dwindle, and expertise to fix and maintain decks begins to disappear. When making any decisions about priorities for a videotape collection, obsolescence of equipment, and availability of equipment (or potential lack thereof) are critical factors to consider.
Equipment Storage[edit | edit source]
Being able to wind and transfer tapes properly is dependent on maintaining functional equipment. It can be as important to preserve equipment in your collection as it is to preserve tape, though it should be noted that the media is more likely to outlive the technology.
Keep the following things in mind when determining equipment needs:
- Buy the best quality equipment available.
- Machinery must be kept clean and properly aligned so it will not damage tape or cause playback errors.
- In particular, keep tape path and heads clean.
- If you plan to keep tapes for many years after the format becomes obsolete, you should keep the service manuals and a stock of spare parts and/or spare decks.
References[edit | edit source]
This article uses material from the Wikipedia article Video which is released under the Creative Commons Attribution-Share-Alike License 3.0.