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3-inch mini-CDs

technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology

Simple gray rule

3-inch mini-CDs

By Al Fasoldt

Copyright © 1991, The Syracuse Newspapers

Compact discs are about 5 inches in diameter and can play for as long as 70 to 75 minutes, right?


Some of them are only 3 inches in diameter. And others can play for 2 ½ hours. These two unusual aspects point up the changing nature of laser-disc high fidelity. CDs are continually improving, just as phonograph technology provided 78-rpm records and then 45s and finally LPs after the first cylinder recordings were introduced more than a century ago.

The 3-inch CD, which can play for up to 20 minutes, was introduced in a few major cities across North America earlier this year, but the big push will come this fall. By that time, Sony, Toshiba and a few other companies will be selling portable mini-CD players in stores throughout the country.

The mini-CD players are not much bigger than "Walkman"-type cassette players, and use the same kind of batteries. Like their larger cousins, CD players that take 3-inch discs can be hooked up to plug-in power supplies and can play their music through home hi-fi systems.

But the intriguing part is that 3-inch CDs don't need to be played on a special mini-CD player. They can be played on any regular CD unit through the use of a plastic ring that fits around the small CD to give it the same dimensions as a regular CD. Many 3-inch CDs will come with an adaptor ring already installed, at least for the first year or so.

The small CDs also can be played on many new-generation standard compact disc players. They have shallow wells in their disc-holding drawers to make sure the 3-inch CDs are properly centered when you load the disc.

At first, you may not see any particular significance to the introduction of tiny CDs that can be played just like full-size discs, but the compatibility between the two sizes represents a major technological victory for Sony and Philips, the co-inventors of the compact disc.

When CDs were being developed in the laboratories of the two companies, some of the engineers wanted the discs to play from the outside in, just like records do. This seemed more natural, especially to consumers weaned on a century of phonograph development.

But other project engineers argued that compact discs should play from the inside out, with a spiral of tracks extending from the center toward the outside edge of the discs as they spin.

Although this would make CDs appear to be playing backward, the inside-out design was best, these engineers said, because the initial playing area—in the CD spirals close to the hub—would be in the same place no matter how big or small the disc was.

Since the hub was a standard size for all CDs, all of them of any diameter would allow the laser head to find the first few seconds of recorded data without difficulty.

And why is that so important? Almost as a secondary design criterion, Philips and Sony had decided to place a unique identifier code within those first bursts of data. This code tells the CD player all about the disc, including, as it turned out, the location of the beginning and end of every track on the disc.

This means, of course, that the player also knows where the last track on the disc ends, and that, in turn, tells the laser playback head not to travel past that point. It is all very elegant and—at least in electronic terms— extraordinarily simple.

As for the CDs that play for as long as 2 ½ hours, they're not extra large, nor do they spin at half speed. Instead, the inventor of double-play CDs took an easier route: He took the left and right stereo signals that normally play at the same time and recorded separate musical performances on each one. First you play one channel, hen you play the other.

The European recording enterprise Harmonia Mundi will be selling double-length CDs late this summer or this fall. Two recordings will come out at first, followed by many others. Both are historic. Richard Wagner's "Ring" in a 1953 original tape, and Beethoven's "Fidelio," also from 1953.

Each recording comes with an unusual accessory—a Y-connector that attaches to the output cables of the CD player. It can be switched among three settings. In the "left" or "right" settings, the signal from that channel is sent through both stereo outputs into your receiver or amplifier. In the "stereo" setting, the adaptor is bypassed.

The double-length Harmonia Mundi discs are full-size, but there's no reason someone couldn't produce 3-inch double-length CDs. They'd play for 40 minutes each, and you could fit about a dozen of them in your shirt pocket. It sure beats carrying around a trunk full of 78s.

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