The Compact Disc​—What Is It All About?

EVER since its introduction to the mass market in the early 1980’s, the laser-​read digital compact disc has been hailed as the greatest breakthrough in sound recording since Edison invented his tinfoil-​cylinder phonograph in 1877 or since the advent of stereophonic sound in the early 1960’s.

In the United States, a report in the trade journal Billboard shows that in 1992, manufacturers shipped over 414 million compact discs but only 22 million vinyl records. The sales are so lopsided that some record companies are no longer producing vinyl records. Still, the shiny little disc remains a mystery to many people. What is digital sound? Is it really as good as it is reputed to be? How does the disc work? And could related technology be used to store and retrieve libraries of information, such as from The Watchtower and Awake!?

Digital Recording​—What Is It?

To understand what digital recording is all about, we first need to have some idea of how the old analog recording works. On the familiar vinyl record, music is recorded as a continuous, undulating groove, like a picture, or analogue, of the sound wave. To reproduce the music, the needle, or stylus, of the record player is placed in the groove on the spinning disc. The stylus follows the groove, and the wiggle of the groove causes the stylus to vibrate. This, in turn, generates a tiny electrical signal that is a replica of what the microphone picked up in the recording studio. The signal is then amplified​—and there is music!

Digital recording takes a different approach. A digital recorder samples and measures the magnitude of the signal at precise intervals​—tens of thousands of times per second—​and records these measured values as numbers, or digits. The measurements are recorded in binary numbers​—the language of computers—​consisting of 0’s and 1’s only. The stream of numbers, or digits, is then processed by a computer and stored, usually on tape. For playback, a computer reads the digits and reconstructs a signal like the original one. This signal is then amplified and​—once again—​there is music!

This process is less affected by the limitations of the recording and manufacturing hardware than is analog recording. This means less noise, less distortion, and fewer other factors that degrade the quality of recordings. In addition, information in digital form can be stored in a very compact format and retrieved easily. Digital recording, one might say, is the natural outcome of the union between a computer and a recorder.

For years record companies have been making digital recordings in their studios. But the playback equipment is far too complicated for home music systems. The real breakthrough in digital recording, as far as consumers are concerned, was in coming up with a playback system economically and technically feasible for the average home user. The result is the digital compact disc (CD) and the compact disc player.

The binary numbers, or bits, are encoded as a series of microscopic pits and flat spaces on the surface of a plastic disc with a shiny aluminum layer. The disc is just four and three quarters inches [120 mm] in diameter. The aluminum layer is sealed under a protective layer of clear plastic. For the music to play, the silvery disc is slipped into a CD player. Instead of a needle, a finely focused laser beam tracks the stream of pits. When the beam hits the microscopic pits, it is scattered, but when it hits the smooth surface, it is reflected back to a sensor. In this way the pits and flats on the surface of the CD are translated into a series of electrical pulses to be deciphered by the sophisticated electronic circuits in the player.

How Good Is It?

But is the CD really better than vinyl records? Well, consider: Since the CD is played using a beam of light rather than a diamond stylus, there is no wear and tear no matter how many times the music is played. Even small blemishes and marks on the surface of the disc will not adversely affect the sound, since the laser beam is focused on the pits and not on the surface of the disc. Gone are those annoying ticks, pops, and scratches that anyone who ever listened to an LP (long-​playing record) is only too familiar with. All of this gives the CD a degree of permanence that the LP cannot match. Theoretically, the compact disc should last forever​—if it is properly manufactured and handled.

The CD’s longer playing time and smaller size are also points in its favor. Over an hour of music can be played without having to get up and flip a record! The CD, being less than a fifth the size of an LP, is also easier to handle and store. In addition, because CD players operate like a computer, many of them can be programmed to play sections of a CD in any preferred sequence or to repeat them. Some players also have search functions that can be used to find any spot in the music quickly. Such convenience features are highly favored by many users.

But what about the sound? Almost everyone who hears a CD for the first time marvels at how clear and lifelike the sound is. The music emerges from a silent background in breathtaking detail. One reason for this is that on a CD the range between the quietest and the loudest music that can be recorded​—called the dynamic range—​is much greater than that on an average LP. This, along with the freedom from noise and distortion, lends greater realism to the music heard on CDs.

On the other hand, an average CD may cost considerably more than an LP. Yet, it must be said that the CD has brought to the general public a degree of refinement in sound reproduction that only a few avid hi-​fi enthusiasts have enjoyed in the past.

Compact Discs and Computers

Recently CDs have taken on an entirely new face because the same technology can be used to store vast amounts of information, or data. Such contents on a compact disc can be easily accessed through a computer having an installed or attached CD reader. Just as any part of a music CD can be accessed quickly on a CD player, with a different type of CD reader, any part of the stored information can be read, searched, or quoted in a matter of seconds by means of properly designed computer programs.

The compact disc has incredible storage capacity. In computer language, it can store over 600 megabytes, the equivalent of 1,000 floppy disks or 200,000 printed pages. In other words, ten sets of a 20-​volume encyclopedia converted into digital form can be stored on just one compact disc! But its advantage is not limited to its huge capacity.

By about 1985, CDs for use in computers began to appear on the market. These were called CD-​ROM, which stands for compact disc read-​only memory. They contained mostly reference material, such as encyclopedias, dictionaries, directories, catalogs, bibliographic and technical data, and archives or collections of various sorts. To begin with, because of their high cost, they were used mostly by libraries and other academic or government institutions. In fact, a disc that a few years ago would have cost several hundred dollars may today be purchased for a small fraction of that.

It did not take long for CD-​ROM to expand beyond being just for storage of text. In the last few years, CD-​ROM discs with color graphics and sound effects began to come on the market. Now not only can you read a biography and see a picture of a certain person but you can also hear a speech by that person. And there are, of course, computer games of all sorts with sound effects and moving color pictures. These so-​called multimedia, interactive systems, which combine the computer and home entertainment, seem to be the wave of the future.

The digital compact disc is truly a technological marvel that can be most useful both for educational and for recreational purposes. Whether it will fulfill its potential remains to be seen.

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The Miniature World of the CD

The name compact disc is no misnomer. On the gleaming surface of this palm-​sized disc are five to six billion microscopic pits laid out in a spiral. If stretched out, the string would be over 3.5 miles [5.6 km] long. Coiled into 20,000 spirals going from the inside of the disc toward the outside, the tracks are packed so tightly together that 60 of them could fit into the groove of an LP (long-​playing record). It has been estimated that if each pit were the size of a grain of rice, the disc would be larger than four football fields.

Because of such minuscule dimensions, CDs must be made in clean rooms where the air is thoroughly filtered. An average dust particle, about five times the size of a pit on the CD, can obliterate enough of the codes to cause error in the recording. “In comparison to our standards of cleanliness,” says an engineer, “a surgical operating room is a pigsty.”

Since the disc spins at up to 500 revolutions per minute as it is played, it is a staggering feat to focus the laser on the tiny pits and to keep it from drifting from the tightly coiled track. To do so, the laser beam is controlled by an amazingly complex guidance system.

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Watchtower Library​—CD-​ROM

The Watchtower Society has always seen fit to use appropriate technological developments in advancing Kingdom interests. In the past the Society was among the first to use color motion pictures, radio networks, and the portable phonograph in proclaiming the good news. Now, the Watchtower Society has released in English the Watchtower Library​—1993 Edition. We feel sure it will prove to be a marvelous tool for Bible study and research.

This new release is truly a library. It contains the text, in electronic form, of the New World Translation of the Holy Scriptures​—With References, the annual bound volumes of The Watchtower from 1950 to 1993 and Awake! from 1980 to 1993, the two-​volume Bible encyclopedia Insight on the Scriptures, and numerous other books, booklets, brochures, and tracts published by the Watchtower Society since 1970. In addition, it contains an index to all Watchtower publications from 1930 to 1993.

Along with this large data base, this CD-​ROM also provides an easy-​to-​use search program that will enable you to search for a word, a combination of words, or a Scripture citation in any of the publications in the Watchtower Library. You can also open directly to any specific publication, right down to a certain chapter, article, or page. The search results can be viewed on the computer screen or copied to a word processor for use in a talk or letter. The program also has a feature for organizing material for personal study projects and for entering your own notes.

It is our hope that with this new instrument, many more will be able to persist in peering into “the perfect law that belongs to freedom” and be blessed for doing so.​—James 1:25.