IEEE A Communications Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page BEF MaGS HISTORY OF COMMUNICATIONS EDITED BY MISCHA SCHWARTZ INTRODUCTION BY EDITOR The article following on the history of the development of the development process, but of the pitfalls and difficulties encoun- CD, written especially for this column by one of the engineers tered and eventually overcome before the system could be who participated in the development effort, should be of interest deemed successful. As another reviewer noted, “ I also appreciat- to all readers of this magazine. As one of the reviewers of the ed the depiction of the human elements that are invariably part article noted, “CDs and successor optical discs are so much a of these projects,” in this case the initial naming of the project or part of our lives, it is fascinating to read about their genesis.” As the reasons for the choice of the final dimensions of the CD. The he goes on to note, “As an engineer, it is equally fascinating and ability of two major companies, Philips and Sony, from two dif- insightful to see how technologies which now seem so obvious ferent parts of the world, to collaborate and come up with such a and inevitable were once open to debate.” I venture to guess that successful product is another fascinating lesson taught by this this is true of almost all technologies, whether large systems or particular history. I suggest you read on to see all of this for your- devices within systems. This is what makes reading about the his- self. tory of a technology written by a participant in the development —Mischa Schwartz process so interesting. We learn not only of the successes in the THE EMERGENCE OF THE COMPACT DISC HANS B. PEEK INTRODUCTION audio industry group within the Philips replicate the information as a consumer Corporation in Eindhoven, the Nether- product by compression or injection This article describes how the compact lands, started to look for smaller and molding of a transparent plastic disc of disc digital audio system, also known as better performing alternatives for the 30 cm diameter. The information the CD system, was the result of the record player and its LP record. The appears on a spiral track consisting of successful merger of two major existing small size of a compact cassette was an microscopic pits separated by flat areas technologies. They are first, optical attractive feature. Although its sound called lands. Finally, after receiving a readout of information stored on an quality improved in the 1970s, mainly reflective coating over which a transpar- optical disc of 11.5 cm diameter, and by using better magnetic tape-coatings ent and protective lacquer is applied, second, the digital coding/decoding and and companding, it became no better the VLP disc is ready for playing. In a digital processing of audio signals. I will than an LP record. VLP player [2, Sec. 2.3, 4] the spiral describe how a complete digital version At that time, when Ottens was look- track on the disc is scanned by a 1 mW of this new audio system gradually ing for a suitable successor of the Helium-Neon laser with a wavelength Q emerged, within Philips, during the record player, the optics department, = 633 nm. The laser beam in the player period 1973–1979. Finally, this paper headed by P. Kramer, of the Philips is focused by an objective lens on the recounts the partnership and collabora- research laboratory in Eindhoven, also information layer of the disc that lies tion between Philips and Sony that known as the Nat.Lab. (Natuurkundig underneath a transparent protective resulted in a common CD standard in Laboratorium), was experimenting with layer. When the spot of the beam falls June 1980 which soon after became the a completely new system for recording on a land, the light is almost totally world standard. More details on the and playback of analog video color sig- reflected and reaches a photodiode. history of the CD not discussed here nals. However, when the spot falls on a pit, can be found in a lively, and accurate, the depth of which is about a quarter of doctoral thesis (in German) by J. Lang THE VLP SYSTEM: A HARDLIMITED the wavelength of the laser light, inter- [1] and in a recent book [2]. ANALOG PRECEDENT OF THE ference and extinction occur, which DIGITAL AUDIO CD causes less light to be reflected and A LOOK INTO A SUCCESSOR OF THE reach the photodiode. The output sig- RECORD PLAYER The Video Long Play (VLP) system, nal of the photodiode is ideally a fair presented to the press in 1972, used a representation of the original recorded In the 1970s the high-fidelity (Hi-Fi) laser to record a video color signal on signal. record player and its LP (long play) an optical disc and another laser in a Unfortunately, there are several vinyl record became increasingly the VLP player for playback. In 1974 the sources of errors that can occur in or weakest product in the audio product VLP was released to the market. Later, on an optical disc. First, small unwant- range. Whereas most audio equipment in 1978, this optical video system was ed particles or air bubbles in the plastic was downscaled in size, this was impos- introduced on the market in the United material, or pit damage, may occur in sible for the Hi-Fi player with its large States, known as LaserVision. the replication process. Second, finger- disc with a 30 cm diameter. Further- In the VLP system a frequency-divi- prints or scratches may appear on the more, the LP record was vulnerable sion multiplex signal consisting of a TV disc when handled. As a consequence, and had to be handled with care. A luminance and chrominance signal plus damage can occur not only to isolated scratch or accumulation of dust could a sound (stereo) signal is frequency pits but also a sequence of pits and spoil the enjoyment of the reproduced modulated (FM) and then hardlimited, even a substantial burst of pits, result- music. after which it is ready for recording on ing in dropout. Aware of these limitations, L. an optical master disc [3]. Production There are two reasons why these Ottens, the technical director of the “stampers” made from this master disc bursts do not seriously affect the pic- 10 0163-6804/10/$25.00 © 2010 IEEE IEEE Communications Magazine • January 2010 IEEE A Communications Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page BEF MaGS IEEE A Communications Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page BEF MaGS HISTORY OF COMMUNICATIONS ture quality in the VLP system. The and tear. Another important feature easy to describe, briefly, the differences first reason, generic to all optical stor- was that an optical system made ran- between the systems described in these age systems, is that the diameter of the dom access possible. Several companies two patents and the Philips-Sony CD beam at the surface of the disc is much such as Sony, Mitsubishi, Hitachi, Pio- standard established in 1980. But let me wider than the diameter of the spot at neer, Toshiba, TEAC Corporation, mention only one crucial difference. the information layer. As a result, local Tokyo Denka Corporation, and Nippon The recording and playback in the CD defects and imperfections at the disc Columbia investigated optical signal system of two digital audio signals dur- surface effectively get blurred and de- registration and playback on 30 cm ing one hour and with for the most part emphasized in the readout signal. This diameter discs. a signal-to-noise ratio (SNR) of 97 dB effect is inherent in reading out a disc After 1972 most of these companies was impossible without using error cor- through a transparent substrate, and started investigating analog signal opti- rection and error concealment. The sig- constitutes one of the essential patents cal recording systems, but at the end of nal mentioned in Gregg’s patent is of the CD system [5]. The second rea- the 1970s some turned to digital signal analog, which excludes the use of an son is that in a TV picture there is a optical recording. Digital signals are error correcting code. Although the sig- high correlation between successive those for which both time and ampli- nal described in Russell’s patent is digi- lines that causes a burst to be less visi- tude are discrete. The signal recorded tal, no error correction is mentioned. ble. Furthermore, there is a high corre- on a VLP is discrete-amplitude but not lation between successive TV frames, discrete-time and is an analog signal. THE ALP PROJECT which in addition enhances the masking Already in 1965, J. T. Russell at the Ottens, who was well informed about of an error burst. Battelle Northwest Laboratory in Rich- the VLP technology, asked his engi- In the period 1972–1979 Philips was land, Washington, considered storage of neers, T. van Alem and L. Boonstra not the only company that was active in digital information on an optical disc. from Nat.Lab., to investigate the possi- the research and development of opti- In 1970 he was granted a patent on an bilities for optical recording and play- cal recording and playback of video, analog-to-digital photographic record- back of four (quadro) Hi-Fi audio audio, and data. For many an attractive ing and playback system (U.S. Patent signals stored on an optical disc with a property of optical systems was also 3,501,586).