Which material is used for making CDs?

Answer 1

A compact disc, or CD, is an optical storage medium with digital data recorded on it. The digital data can be in the form of audio, video, or computer information. When the CD is played, the information is read or detected by a tightly focused light source called a laser (thus the name optical medium). This article will focus on audio compact discs, which are used to play back recorded music.

The history of the compact disc can be traced back to the development of electronic technology and particularly digital electronic technology in the 1960s. Although the first applications of this technology were not in the recording area, it found increasing use in audio components as the technology evolved.

During the same period, many companies started experimenting with optical information storage and laser technology. Among these companies, electronic giants Sony and Philips made notable progress in this area.

By the 1970s, digital and optical technologies had reached a level where they could be combined to develop a single audio system. These technologies provided solutions to the three main challenges faced by the developers of digital audio.

The first challenge was to find a suitable method for recording audio signals in digital format, a process known as audio encoding. A practical method of audio encoding was developed from the theories published by C. Shannon in 1948. This method, known as pulse code modulation (PCM), is a technique that samples a sound during a short time interval and converts the sample to a numerical value that is then modulated or stored for later retrieval.

The storing of audio signals in digital form requires a large amount of data. For instance, to store one second of music requires one million bits of data. The next challenge, therefore, was to find a suitable storage medium to accommodate any significant amount of sound. The solution to this problem came in the form of optical discs. An optical disc can store large amounts of data tightly compressed together. For example, one million bits of data on a CD can occupy an area smaller than a pinhead. This information is read by means of a laser beam that is capable of focusing on a very narrow area as small as 1/2500th of an inch.

The final challenge of digital audio was to process the densely packed information on compact discs quickly enough to produce continuous music. The solution was provided by the development of integrated circuit technology, which allow the processing of millions of computations in just micro-seconds.

By the late 1970s, a common set of standards for the optical storage discs had been developed by the joint efforts of Sony and Philips. A consortium of 35 hardware manufacturers agreed to adopt this standard in 1981 and the first compact discs and compact disc players were introduced in the market in 1982.