Cd skiva material
Compact discs must be manufactured under very clean and dust free conditions in a "clean room," which is kept free from virtually all dust particles.
Learn What CDs/DVDs Are Made of & The Secret Behind Optical Disk Technology
A CD usually weighs around. The storing of audio signals in digital form requires a large amount of data. The solution to this problem came in the form of optical discs. A reflective aluminum layer is applied, followed by a clear acrylic protective layer, and finally the label. The positioning hole in the middle is. During the same period, many companies started experimenting with optical information storage and laser technology.
The compact disc is designed strictly according to the standards established by Sony and Philips in order to maintain universal compatibility. A compact disc is a deceptively simple looking device considering the technology required to make it. For example, one million bits of data on a CD can occupy an area smaller than a pinhead. A consortium of 35 hardware manufacturers agreed to adopt this standard in and the first compact discs and compact disc players were introduced in the market in Making a compact disc involves first preparing a glass "disc master.
This spiral or track consists of a series of indentations called pits, separated by sections called lands. A layer of lacquer is spin-coated onto the CD to protect the metal. The solution was provided by the development of integrated circuit technology, which allow the processing of millions of computations in just micro-seconds. When the final master version is ready, its information is transfered onto a plastic disc. A compact disc, or CD, is an optical storage medium with digital data recorded on it.
This article will focus on audio compact discs, which are used to play back recorded music. The digital data can be in the form of audio, video, or computer information. CDs consist of three layers of materials:. In electroforming, metal layers are deposited on the glass master using electric currents. The air in the room is specially filtered to keep out dirt, and occupants of the room must wear special clothing.
Ever since the invention of the phonograph in , music has been a popular source of home entertainment. Because an average dust particle is times larger than the average pit and land on a CD, even the smallest dust particle can render a disc useless. The surface of a CD is reflective because the disc is coated with a thin layer of aluminum or sometimes gold. The final challenge of digital audio was to process the densely packed information on compact discs quickly enough to produce continuous music.
For instance, to store one second of music requires one million bits of data. By the s, digital and optical technologies had reached a level where they could be combined to develop a single audio system. The sensor sees more light when it is on a land than when it is on a pit, and these variations in light intensity are converted into electrical signals that represent the music originally recorded.
Beteckningen CD syftar oftast på vanliga ljudskivor som följer standarden CDDA. The next challenge, therefore, was to find a suitable storage medium to accommodate any significant amount of sound. The recorded data on the CD takes the form of a continuous spiral starting from the inside and moving outward. 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.
Compact Disc
A standard CD can store up to 74 minutes of data. Andra standarder är CD+G (ljud-CD med grafik), CD-MIDI (ljud-CD med MIDI-spår), CD-i (interaktiv CD) och VCD (video-CD, vilket inte är samma sak som DVD, även om de flesta DVD-spelare även kan spela VCD). However, most CDs contain only about 50 minutes of music, all of which is recorded on only one side of the CD the underside. By the late s, a common set of standards for the optical storage discs had been developed by the joint efforts of Sony and Philips.
Although the first applications of this technology were not in the recording area, it found increasing use in audio components as the technology evolved. An optical disc can store large amounts of data tightly compressed together. In recent years, the compact disc has become the playback medium of choice for recorded music. The first challenge was to find a suitable method for recording audio signals in digital format, a process known as audio encoding.
The history of the compact disc can be traced back to the development of electronic technology and particularly digital electronic technology in the s. Some manufacturers use a silver or even gold layer instead of the aluminum layer in the manufacture of their compact discs.
The shiny metal layer reflects the laser that is used to read or write to the device. These technologies provided solutions to the three main challenges faced by the developers of digital audio. En CD-skiva är 12 cm i diameter. A practical method of audio encoding was developed from the theories published by C. Shannon in 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.
A tiny laser beam moving along the track reflects light back to a photo sensor. Among these companies, electronic giants Sony and Philips made notable progress in this area.