History - Technical - Testimonials

A historical overview of the development of the Compact Disc

As staggering as the release of the compact disc player was in 1982, the technology and theories which allowed it to be born were long in development. In 1841, the great mathematician Augustin-Louis Cauchy first proposes the sampling theorem.
Nearly 80 years later J.R. Carson publishes a mathematical analysis of time sampling in communications. In a 1928 lecture at the American Institute of Electrical Engineers Harry Nyquist provides proof of the sampling theorem in "Certain Topics in Telegraph Transmission Theory". In 1937, A. Reeves proposes pulse code wave modulation (PCM). In 1948, John Bardeen, William Shockley, and Walter Brattain invent the bipolar junction transistor at Bell Labs--compact digital circuitry is a reality. Two years later, in 1950 Richard W. Hamming publishes significant work on error correction and detection codes. In 1958 C.H. Townes and A.L. Shawlow invent the laser. In 1960 R.C. Bose publishes binary group error correction codes. That same year I.S. Reed and G. Solomon publish error correction codes to be used in the CD player 22 years later. Also early computer music experiments take place at Bell Labs.
Fifteen years before consumers see the first player, NHK Technical Research Institute publicly demonstrates a PCM digital audio recorder with a 30 kHz sampling rate and 12-bit resolution.
Two years later, Sony Corporation demonstrates a PCM digital audio recorder with a 47.25 kHz sampling rate and 13-bit resolution. A hemisphere away, Dutch physicist Klaas Compaan uses a glass disc to store black and white holographic images using frequency modulation at Philips Laboratories. Four years later, in 1973 Philips engineers begin to contemplate an audio application for their "video" disc system. A prototype disc with a 44 kHz sampling rate is run through a 14-bit digital-to-analog converter and exhibits a signal-to-noise (S/N) ratio of 80 dB in monaural. Now a research frontier, Mitsubishi, Sony, and Hitachi all demonstrate digital audio discs at the Tokyo Audio Fair in 1977.
One year later, Philips joins with its recording subsidiary Polygram Records to develop a worldwide digital audio standard. In March 1979, Philips demonstrates a prototype compact disc player in Europe. Sony joins the Philips/Polygram coalition after Matsushita declines.
In June of 1980, the coalition formally proposes their CD standard. A year later in 1981, Sharp successfully mass produces the semiconductor laser. This step was crucial to delivering a consumer product.
In Fall of 1982 nearly 150 years of work comes to fruition and Sony and Philips introduce their respective players to consumer in Europe. The following spring, the player is introduced in the United States.
Twenty years later, the improvement of digital audio continues at a rapid pace and the analog format that was so prevalent in 1982 has all but disappeared.

A Fundamental Introduction to the Compact Disc Player

The compact disc player has become one of the most ubiquitous pieces of consumer electronics equipment in use today. Tens of millions of players have been sold to date. However, as pervasive as the compact disc player's presence is, the beauty and complexity of its design and operation are underappreciated by most users. This brief text attempts to inform the reader of the basic fundamentals of the compact disc player. It is a assumed that the reader has a basic knowledge of the fundamentals of signal processing, although it is certainly not a prerequisite for learning a great deal from the reading.

Strengths of the Digital Domain, weaknesses of the Analog Signal
Since Thomas Edison made the first audio recording on a foil covered cylinder in 1877, the field of audio recording has grown and matured. Edison's process and many others that followed were all based on a common process; the reproduction of an audio signal from a mechanical or electrical contact with the recording media--this is the realm of analog audio. After nearly 100 years, analog audio has reached a mature state and nearly all of its shortcomings have been addressed to the point that further improvements become financially prohibitive for the average consumer.
The very nature of the analog signal leads to its own shortcomings. In the analog domain, any waveform is allowable; therefore the playback mechanism has no means to differentiate noise and distortion from the original signal. Further, in an analog system every copy made introduces more noise than its parent. This fact is due to both the playback and recording mechanism which must physically contact the media, further damaging it after every pass. Every analog system also carries the side effect that the total system noise is the summation of all distortion and noise from each component in the signal path. Finally, analog equipment is of limited performance, exhibiting: an uneven frequency response (which requires extensive equalization), a limited 60 dB dynamic range, and a 30 dB channel separation--which affects stereo imaging and staging.
The need for a new audio format is apparent, and digital audio fills the performance shortcomings of analog audio. The beauty of the digital audio signal is that noise and distortion can be separated from the audio signal. A digital audio signal's quality is not a function of the reading mechanism nor the media in a properly engineered system. Performance parameters such as frequency response, linearity, and noise are only functions of the digital-to-analog converter (DAC). Performance parameters indicative of a digital audio system include full audio band frequency response of 5 - 22,000 Hz, 90+ dB dynamic range, and a flat response across the entire audio band.
The final strength of digital audio is the circuitry upon which it is built. First, due to a large degree of circuit integration digital circuits do not degrade with time as analog circuits do. Further, for all practical purposes, a digital signal will suffer no degradation until distortion and noise has become so great that the signal is out of its voltage threshold. However, this threshold has been made intentionally large expressly for this reason. The high level of circuit integration also means that for the same given task, the digital circuitry will cost far less than its analog counterpart.
The only real theoretical limitation to the accuracy of a digital signal is the quantity of numbers in the signal representation and the accuracy of those numbers. These are both known and controllable design parameters.

The pictures shown here give a clear insight on how the reading of the digital data on the CD actually occurs, and although the technology may seem quite intruiging, the basic technique is actually pretty straightforward and easy to comprehend.
A low-intensity laser beam is reflected by a series of pits on the metallized plastic substrate of a rotating disk, and registered by an optical pickup. The pis are arranged along a spiral path extending outward from the center; the relative length of the pits and the spaces between them (called “land”) is varied, producing changes in reflectivity by which the 1’s and 0’s are encoded.
CD rotational speed varies from about 3.5 to 8 revolutions per second, according to the location being read on the disk, which is either 120mm (standard size) or 80mm in diameter, and 1.2millimeters thick.

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