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A time bomb in your compact disc?

technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology

Simple gray rule

A time bomb in your compact disc?

By Al Fasoldt

Copyright © 1991, The Syracuse Newspapers

Compact discs don't wear out, but they could self-destruct.

Those are the tentative findings of researchers in the United States and Japan. They looked at the way CDs are manufactured and determined that the plastic sandwich around the disc can sometimes go bad.

This layer of clear plastic on the upper and lower surfaces of the disc normally protects the metallic layer on the inside. The metallic layer is very shiny, and that's what makes the CD work. The laser beam shines out of the CD player, travels through the clear plastic and then bounces off the metallic layer and heads back where it came.

That's all very neat and clever. But if the metallic layer isn't shiny, the whole process falls apart.

That's what apparently happens with some compact discs. Researchers say they found that some discs went bad when the plastic layer either peeled away or deteriorated in some fashion. This let air get into the discs, and the air caused the metallic layer to oxidize.

And when that happened, the metallic layer turned cloudy. The laser beam no longer bounced back into the player, and the discs became little more than expensive Frisbees.

The discs that went bad were about 5 years old, or older. CDs were designed to last a lot longer than that—at least 20 years, according to the engineers who developed CDs in the early 1980s.

Is it a fluke that some compact discs don't seem to last very long? Maybe. It's likely that quite a few CDs out of the millions made every year slip through with defects.

But some experts say the problem could be common to many CDs. Over many months, chemicals in the disc may be reacting in a subtle way. The result could well be the breakdown of the plastic sandwich.

The trouble with all this is that we don't have any way of testing the life expectancy of compact discs except by waiting for them to grow old. Scientists are an impatient bunch, and they don't want to wait around for 20 years to see what happens to CDs.

So, the researchers are looking for ways to speed up the clock. Experts from the Audio Engineering Society and the American National Standards Institute have formed a commission to study the way CDs and similar objects age. They especially want to come up with an industry-standard method of simulating the aging process.

Syracuse University's William Storm is co-chairman of the commission. Storm, who heads SU's audio research, says he wants the audio industry to find a way of adding a life-expectancy rating to such things as compact discs.

If his idea is adopted, CDs could one day have an "LE" designation—for life expectancy—printed on the CD and on the box, just as they have a three-letter digital code (such as "DDD") today. An "LE 7," for example, would indicate that the manufacturer expects the disc to last at least seven years.

This would give consumers a way to choose quality levels. Cheap CDs that have ratings of, say, "LE 5" might be fine for an Iggy Pop collection, but you'd probably want to look for ratings of "LE 25" or more for Beethoven's Ninth.

Storm is also trying to get manufacturers to recognize another life-expectancy problem—the rapid pace of change in consumer technology. An excellent example comes from the field of digital tape recording.

Just as we are beginning to accept DAT recorders—which use tiny tapes that work like videocassettes—along comes an announcement from two manufacturers that they'll have an entirely different digital tape system in a year or two.

Should we buy a DAT recorder or wait for the new design? It is just this sort of puzzle that Storm would like to see eliminated. All manufacturers have to do is agree in advance on various standards.

A look at the brief history of consumer electronics shows how much the industry needs to get its act together. After the long marketing wars over Beta and VHS video formats, the stumbling over three competing ways of creating four-channel sound and the current fiasco over making a workable high-definition (sharper picture) television system, any improvement will be welcome.

I wish William Storm lots of luck. He'll need it.

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