Pohlmann - The Compact Disc Handbook - Introduction

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From its Dutch and Japanese origins in June 1980, the compact disc system has prospered beyond the wildest dreams of its inventors. The original audio CD was one of the most successful new electronic products ever introduced; everyone was surprised by its rapid acceptance by music lovers. Over the next few years the biggest news concerned shortages, particularly of discs themselves. Then the disc caught the attention of data lovers as well. CD-ROM quickly started its own acceleration into the market of mass storage. CD-V added high fidelity video to the family. As if that wasn't enough, CD-I's future looks similarly promising as an interactive audio-video medium. Of course, while reading data is fun, writing data is even more fun. Thus a standard for write-once CDs was introduced, and erasable CD technology has been developed. Furthermore, CDs with graphics and MIDI information and mini-CDs were also introduced into the marketplace. In short, the compact disc family is a hit and already encompasses more topics than one book could comprehensively cover.
Exactly how important is it to bone up on a new technology such as the compact disc? How significantly will it influence our everyday lives, and for how long? There are a number of factors that determine the lifespan of a technology. Manufacturing cost, product performance, market penetration, user boredom, and innovative competition all move technological evolution forward and heighten expectations. As far as the CD family goes, it is safe to say that the future looks bright indeed. Its market share is just beginning to expand, and new and consequential applications are undoubtedly waiting to be discovered by insightful entrepreneurs. Of course, no technology, except the very primitive kind, lasts forever, and someday (perhaps relatively soon) the CD will be only a curiosity. Fittingly, the discs themselves should long outlast their usefulness.

Meanwhile, this handbook covers all the fundamentals of the audio CD and should prove useful to anyone delving into this technology, especially for the first time. Hopefully, it will answer all your questions about audio CDs, and pave the way to a greater understanding of the derivative CD formats.

This little opus, composed of seven chapters, starts from the basics and proceeds onwards and upwards. Theoretical topics are treated expeditiously, and mathematics have been avoided almost entirely. The emphasis is on practical, understandable, useful information.

Chapter One is an introduction to the fundamentals of digital audio theory. Digital signals are contrasted to the analog variety, and the pros and cons are discussed. Just for fun, a brief history of the events leading to the CD are chronicled. In addition, the compact disc is weighed against its predecessors. The chapter, like all the chapters, concludes with a list of references for further reading.

Chapter Two begins our technical discussion. Sampling and quantization, the key analytical methods of digitally interpreting analog signals, such as audio waveforms, are presented. Aliasing, a negative attribute of sampling, and dither, a panacea for problems arising from quantization, are examined. Pulse code modulation, a particularly clever method of encoding digital audio data, is presented. Finally, a practical audio digitization system is used to consolidate all the theory.

Chapter Three examines the technical theory underlying the compact disc system. The encoding process leading to the plastic disc is examined. The disc itself is an impressive piece of handiwork, particularly at the microscopic level, so the intricacies of data pits are presented. The use of error correction is unprecedented in audio storage; the methods used to safeguard the CD's data are discussed. The bit stream from the disc is processed just as heavily, and oppositely, to the input bit stream. The signal processing circuitry comprising every CD player is examined. The chapter concludes with a look at the non-audio subcode data, which is stored on every CD and used to control playback.

Chapter Four zeros in on CD player design, starting with the laser pickup as it reads data from the disc at a rate of 4.3218 million bits per second. To assist the pickup in its difficult task, electro-mechanical circuits are used for focusing the beam and keeping it on track. Digital filters must be used to process the waveform before it is presented to the ears. Digital filters and digital signal processing in general are carefully introduced. The digital-to-analog converter's job is to transform data back into an audio waveform. These output stages are summarized with a look at a specific chip set. The chapter concludes by examining low-bit D/A conversion and the AES/EBU and SPDIF standards, serial transmission formats used to convey data from one digital audio device to another.

Chapter Five brings the discussion back to the macroscopic level of the consumer. User notes are presented on a variety of topics. Different player designs are examined and critiqued. Specifications provide a means to distinguish good players from the merely mediocre; measurement techniques are examined. Tips are given to assist in purchasing a CD player. Player care is also important, including the do's and don't's of preventative maintenance. Your disc collection will probably represent a bigger investment than the player; it is wise to take care of your discs, and to be able to evaluate any defects that may be present.

Chapter Six carries the discussion to the diverse versions of the compact disc system. The audio CD was only the first of several CD family members. CD-ROM uses the CD's vast storage potential for non-audio applications, such as data bases and software programs. CD-I merges video with audio on CDs. Imagine a new kind of publishing: combined illustrated, printed and talking books. DVI provides yet another format for interactivity and the Photo CD format brings high-quality photographic images to the disc. CD-V merges the CD’s digital audio format with that of high quality analog video optical storage. The CD-R format offers users the chance to permanently record their own data. Several fully recordable/erasable CD methods, including magneto-optics and phase-change technology, allow users to record and erase data. Although incompatible with the CD, the MD format promises to expand optical disc applications. CD+G/M utilizes subcode storage capacity to provide graphics and MIDI output from audio CDs. CD-3 is a mini-sized CD, for applications where shorter playing times are sufficient.

Chapter Seven is an examination of the technology of compact disc manufacturing. The discussion concentrates on the foremost production method, injection molding of polycarbonate plastic. Preparation of master tape, the mastering of the glass disc, the production of pressing molds, injection molding, metallization, spin coating, printing, packaging, and quality control are all discussed. Alternative manufacturing methods may simplify the task of making discs; these new methods are explained.

A Glossary containing definitions of key technical terms and abbreviations rounds out the presentation.