Compact Disc player

Background

A compact disc, also popularly known simply as a CD, is an optical storage medium with digital data recorded on its surface. A compact disc player is a device that reads the recorded data by means of an optical beam and accurately reproduces the original information (music, pictures, or data). Because the player reads the information by optical means, there is no physical wear and tear on the disc. The basic technology used in all compact disc players is essentially the same, whether the player is designed for audio, video, or computer applications. This article will focus on players designed for audio (specifically, home audio) applications.

The history of the compact disc system can be traced back to the early 1970s, when rapid advancement in digital electronics, laser optics, and large scale integration (LSI) technologies took place. Many companies started exploring the possibility of storing audio signals in optical form using digital rather than analog means. A practical method of modulating the audio signals was found using theories published in 1948 by a scientist named Claude E. Shannon. This method, known as Pulse Code Modulation (PCM), samples audio signals during a short time interval and then converts the samples into numerical values for storage in digital format.

The storage of audio in digital format (known as audio encoding) requires large amounts of data. For example, storing one second of audio information requires one million bits of data. Optical discs capable of storing billions of bits of data in a very small area were found ideal for such applications. An optical disc can store up to one million bits of data on an area as small as a pinhead. Once the technologies for recording and storing digital audio were found, manufacturers started looking for ways to read and process the data stored in such a small area. Experiments with laser devices (a laser emits a very narrow beam of light capable of focusing on a very small area) proved quite successful. The development of LSI techniques meant that the huge amount of data stored on the disc could be processed fast enough to provide continuous music. The stage was now set for the development of a complete compact disc system.

Although many companies participated in early research and experimentation with the various technologies involved in a compact disc system, two companies—Sony of Japan and Philips of the Netherlands—are credited with successfully merging these technologies into a complete system. The two companies collaborated to develop specific standards for the compact disc system, and a consortium of 35 manufacturers agreed to adopt these standards in 1981. The first compact disc players were introduced in the European and Japanese markets in late 1982 and in the United States in early 1983.

Raw Materials

A compact disc player is a very sophisticated piece of electronic equipment. The simple exterior contains complex interior mechanisms to read and process audio signals into very clear and crisp music. The various components include a housing cabinet, an optical pick-up assembly, and printed circuit boards (PCBs), which contain microchips that direct the electronic processes of the system.

The cabinet that houses the maze of components is usually made of light, reinforced aluminum. The laser is a small glass tube filled with gas and a small power supply to generate a laser beam, while the photodiode—a semiconducting part that the light that is reflected from the compact disc into an electrical signal—is generally made of silicon or germanium. The lenses and mirrors in the optical pick-up are made of highly polished glass or plastic. This assembly is housed in its own plastic enclosure. The majority of the electronic components—resistors, transistors, and capacitors—are contained on microchips attached to PCBs. The base material of these components is usually silicon. The hardware that connects the various subassemblies together consists of a variety of metal and plastic nuts, screws, washers, pulleys, motors, gears, belts, and cables.

Design

A compact disc is a 4.75 inch-diameter (12.065 centimeters) polycarbonate plastic disc containing approximately 74 minutes of audio information. Not all the information on the disc is music; some of it is used for error detection, synchronization, and display purposes. Information on a CD is encoded on a spiral track in the form of indentations called lands and pits that represent binary highs and lows. It is these indentations that the CD player's laser "reads."

Conceptually, the design of a CD player resembles that of a phonograph (record) player. Like a record, the compact disc is rotated on a turntable, and the audio is read by a pick-up device. However, unlike a record player, the motor does not rotate the turntable at a constant speed but adjusts it in accordance with the distance of the pick-up from the center of the turntable. Furthermore, the pick-up device in a CD player is not a mechanical stylus (a needle) but an optical laser beam that does not come into physical contact with the compact disc. This laser focuses its beam on the disc track that contains the lands and pits, and the CD player's detector (the photodiode) senses the difference between the light reflected from the lands and that reflected by the pits. The photodiode turns this reflected light into an electrical signal. Relayed to the electronic circuit board, this signal is then converted back to sound.

There are basically three subassemblies in a compact disc player: the disc drive mechanism assembly; the optical pick-up assembly; and the electronic circuit board assembly, which coordinates the other systems inside the player and which includes the servo mechanism and data decoding circuitry. By sending signals to the servo mechanism, the circuit board adjusts the motor speed, focusing, and tracking of the optical pick-up; manages the flow of data to the decoding circuitry; and provides display information in response to the various buttons on the control panel.

The disc drive mechanism consists of a spindle that holds the CD and a motor that rotates it. The motor, called the spindle motor, is mounted underneath the plastic disc loading tray or turntable. A separate motor mounted on the chassis (the base or frame of the CD player) moves the loading tray in and out of the player; this is done by means of a gear that is attached to the motor and that also operates a larger gear to raise and lower a clamp for holding the disc in place.

The optical pick-up consists of a laser, a photodiode, and various lenses and mirrors. The entire subassembly slides back and forth on rails and is controlled by the servo mechanism that receives directing signals from the circuit board. The optical pick-up is usually located underneath the clamp that positions the disc, while the motor that moves the assembly is mounted on the chassis close to the rails. The mechanism works by directing a laser beam through lenses and mirrors onto the underside of the compact disc. The lenses and mirrors keep the beam properly focused. If the beam hits a pit on the disc, no light is reflected and the photodiode remains disengaged. If the beam hits a land, light is reflected back through the lenses and mirrors onto the photodiode, which then generates an electrical signal. This signal is transferred to the electronic circuit board assembly, where it is converted by the data decoding system into audio signals for playback.

The electronic circuit board assembly consists of printed circuit boards that contain the circuitry for the servo mechanism, which operates the optical pick-up system, data decoding, and control system. There are many integrated circuits chips, microprocessors, and large scale integrated components on the board assembly.

The Manufacturing
Process

In today's manufacturing environment there is no single method of manufacture and assembly. Products are increasingly made as subassemblies and brought together as larger subassemblies or as the final product. Robotics and computer run lines allow for virtually any part to be installed in any state of the subassembly at any point in the process. The sequence can be changed in minutes to allow for modifications or quality control check points. The manufacturing process detailed here, therefore, follows a similar approach to the actual manufacturing process used in the industry. The process is first described in terms of the various subassemblies and then the description details how the various subassemblies are brought together to make the final product.

Optical pick-up subassembly

• Purchased from outside contractors, the laser and the photodiode are installed beneath the disc clamp. The various lenses and mirrors in the assembly must be properly spaced and aligned so that they can focus and direct light as necessary. The whole assembly is then housed in a plastic case. The case is made by the one of the usual plastic forming processes such as extrusion or injection molding, while the lenses and mirrors (usually silicon) are cut into the proper shape and then finely polished with abrasives. The semiconducting photodiode is made by preparing and polishing a substance such as silicon or germanium and then adding impurities to create layers. Electrical contacts are then added. After the optical components are in position, the gears and belt that will help to position the optical pick-up are put in place.

Disc drive subassembly

• Next, the motor that will move the optical pick-up is connected to the gears and belt and placed on the chassis. The loading tray is now centered, and the spindle motor that will rotate the disc is installed. After the clamp to which the optical pick-up has been attached is positioned adjacent to the loading tray, the tray, clamp, and pick-up motor are installed in the loading drawer, which is placed in the CD player's cabinet.

Electronic circuit board subassembly

• Last to be assembled are the electronic components. Designed by engineers using computer-aided design (CAD) packages, the circuit boards consist of a copper-clad base that has a pattern transferred onto it(masking) through screen printing or a similar method. After being coated with a photosensitive material, the patterned areas are etched away chemically to create a multi-layered board—the layers comprise the various transistors and capacitors that make up the circuits. The tiny microchips (usually made of silicon) that are mounted on the board are made in the same way, except on a much smaller scale. Depending on the manufacturer, the CD player may have one large circuit board or several smaller boards. After they have been attached to the panel or panels, the circuits are attached to the CD player's front control panel, the switch assembly, and finally the power supply.

Final assembly

• Once the various subassemblies are ready, they are connected and interfaced together to complete the final assembly. Most of the work performed at this stage is done by human workers. The CD player is now tested and sent for packaging.

Quality Control

As previously noted, a compact disc player is a very sophisticated device, and strict quality control measures are adopted from the initial to the final stage of the manufacture to ensure the proper functioning of the player in accordance with industry standards.

Because so many of the components in a compact disc player are made by specialized vendors, the player manufacturer must depend on these vendors to produce quality parts. Some of the most crucial elements are those in the optical pick-up assembly. The lenses and mirrors used in the laser pick-up, for instance, are made of high quality glass, and human contact must be avoided during the manufacturing process to keep their surfaces clean and smudge free. Similarly, the electronic circuit components must be made in a "clean room" environment (containing special air filters as well as clothing requirements), because even a single dust particle can cause malfunctioning in the circuitry. The circuit boards and chips are tested at many levels by diagnostic machines to pinpoint faults in the circuits.

As for quality control by the player manufacturer, the disc drive assembly is inspected for proper alignment of the motor, spindle, loading tray, and the various gears. In addition, the optical pick-up is checked for proper alignment of lenses and the laser beam. Once the subassemblies are tied together in the cabinet, all wiring connections are inspected for proper electrical contact and correct interface with the other components. Visual inspections to check belts, pulleys, and gears are an integral part of the quality control process. The final inspection consists of playing a test disc that generates special signals and patterns, enabling workers to track down faults in the system. In addition, the various front panel switches and buttons are checked to ensure that they perform the functions indicated and display the appropriate information on the panel.

The Future

The CD system technology has come a long way in the last few years, and new applications for compact disc systems are being discovered every day. The market has already seen the introduction of CD-ROMs, CD-Videos and CD-Interactive. The latest product to attract consumer attention is Kodak's Photo-CD, which can display photographs on television and computer screens. These pictures can be edited or cropped by the user, just like clip art images.

Audio CD systems will see the introduction of many new features in the coming years. Players featuring advanced remote control functions are now in the development stage. These functions will allow the user to display information on the remote control unit itself, such as song titles, artist names, and the actual lyrics of the songs. Compact discs capable of both recording and playback, like a cassette tape, are also in the works. The CD's vast storage capabilities also lend itself to many broad-based multimedia applications, and it is quite possible that compact discs will become the common medium of data exchange for all audio, video, and computer applications.

Where To Learn More

Books

Brewer, Bryan and Ed Key. The Compact Disc Book. 1987.

Davidson, Homer L. Troubleshooting and Repairing the Compact Disc Player. 1989.

Pohlman, Ken. Principles of Digital Audio. 1985.

Schetina, Erik. The Compact Disc. 1989.

Williams, Gene B. Compact Disk Players. TAB Books, 1992.

Periodicals

Matzkin, Jonathan, Rock Miller, Gayle C. Ehrenman, et al. "CD-ROM Drives: Finally Up to Speed," PC Magazine. October 29, 1991, p. 283.

Ranada, David. "Loose Bits," High Fidelity. March, 1986, p. 22.

Shah, Prasanna. "Music of the Bitstream," Audio. January, 1991, p. 56.

[Article by: Rashid Riaz]

This article is about the electronic device. For the Microsoft Windows Software, see CD Player (Windows).

CD, DVD and SACD player

A Compact Disc player (often written as compact disc player), or CD player, is an electronic device that plays audio Compact Discs. CD players are often installed into home stereo systems, car audio systems, and personal computers. They are also manufactured as portable devices. Modern units support other formats in addition to CDs, such as DVDs, CD-ROMs with audio files and video CDs. DJs often use players with an adjustable playback sampling rate to alter the pitch of the music programme. Many modern CD players also play MP3 CDs. CD playback functionality is available on all modern CD-ROM/DVD-ROM drive equipped computers as well as on DVD players and CD-ROM/DVD-ROM based game consoles.

Contents 1 Physical description 2 Tray Design Evolution 2.1 Tray Loading 2.2 Vertical Loading 2.3 Top Loading 2.4 Tray Load with Sliding Mechanism 2.5 Tray Load with Dampers 2.6 Slot Loading 3 Pickup mechanisms 4 Function 5 Interface 6 CD changer 6.1 Prior art 6.2 Main types of CD changers 6.2.1 External cartridge 6.2.2 Internal cartridge 6.2.3 Carousel 6.3 Evolution 6.4 Computer-based changers 7 See also 8 References 9 External links

Physical description

A 1980s era Denon CD deck.

Many CD players are contained in a plastic and steel casing which also houses the electrical system and the user interface.

The housing of a portable CD player also contains ports used to connect the player to a powered or unpowered speaker, headphones and/or a power system (see electrical wiring in the United States or in the UK). A portable CD player generally contains an internal power source in the form of batteries.

The housing of a stand-alone CD player contains speakers and perhaps a radio and/or tape deck. CD players used in component audio systems contain a power source, the user interface, and numerous ports to connect the player to the various parts of an audio system.

Tray Design Evolution

Tray Loading

Sony released the world's first CD Player called the CDP-101^[1] in 1982 utilising a slide-out tray design for the CD. As it was easy to use and manufacture, most CD player tray designs had followed this style of tray ever since. However there have been some notable exceptions.

Vertical Loading

During the launch of the first prototype CD player 'Goronta'^[2] by Sony at the Japanese Audio Fair in 1982, Sony showcased the vertical loading design of the CD player. Although the prototype's design was never really put into actual production, it was for a time adopted for production by a number of early Japanese CD player manufacturers including Alpine/Luxman, Matsushita under the Technics brand, Kenwood and Toshiba/Aurex. For the early vertical loading players, Alpine sourced their AD-7100 player designs for Luxman^[3], Kenwood and Toshiba (using their Aurex brand). Kenwood added their 'Sigma Drive' outputs to this design as a modification. A picture of this early design can be seen on the Panasonic website.^[4]

Top Loading

Top-loading CD player and external DAC.

In 1983, at the US and European launch of the CD format, Philips with their CD100 CD player (sold as Magnavox in the US), showcased the first top loading CD tray designs. The design had a clamp on the lid which meant the user had to close this over the CD when it was placed inside the machine. Apart from having no motors accessing a movable tray, thus interfering with the player's sound quality, as the disc was clamped right down within the player, it implied better sound quality. This was one of the primary reasons manufacturer Meridian created their MCD CD player,^[5] whose chassis design was derived from the Philips CD100.

Apart from being adopted on various stereo equipment designs such as mini components, over the years only a handful of hi-fi quality top loading tray CD players had been made. The most notable were Luxman's D-500 and D-500X series^[6] players, and Denon's DP-S1,^[7] both launched in 1993.

Tray Load with Sliding Mechanism

Meridians 200 and 203 players were the first players to adopt tray loading with sliding play mechanism. Basically as the tray came out to collect the CD, the entire player's transport system also came out as one unit. The players were also the first to utilise the CD Transport design whereby the audio electronics were separate from the CD drive mechanism itself to reduce jitter and distortion.

Tray Load with Dampers

A few companies produced CD players with dampened trays. The dampers were rubber grommets built into the tray to reduce distortion. Yamaha's CDX-1000 CD player was a good example of this design.

Slot Loading

Slot loading is the preferred loading mechanism for car audio head units, the Apple MacBook, PlayStation 3, amongst other audio players. There is no tray that pops out, and a motor is used to assist disc insertion and removal. Mini-CDs and non-circular CDs may have troubles with insertion and/or ejection.

Pickup mechanisms

Underside view showing a radial type tracking mechanism with screw drive.

Two types of optical tracking mechanisms exist:

• the swing-arm mechanism, originally designed by Philips^[8] - the lens moves at the end of an arm, very much like the old turntables.
• the radial mechanism, designed by Sony to avoid using Philips patent, which is the one used in most CD players nowadays (because it is cheaper) - the lens moves on a radial rail. It is also known as 3-beam linear tracking.

The swing-arm mechanism has a distinctive advantage over the other in that it doesn't "skip" when the rail becomes dirty. The swing arm mechanisms tend to have a much longer life than their radial counterparts. The radial mechanism works best for CD-ROMs, though, as the speed of the disc increases.

Function

Teac CD player anatomy.

Philips Portable CD player disassembled.

A CD player has three major components: a drive motor, a lens system, and a tracking mechanism. The drive motor rotates the disc between 200 and 500 revolutions per minute. The tracking mechanism moves the lens system along the spiral tracks in which information is encoded, and the lens reads the information using a laser beam, typically produced by a laser diode. The laser reads information by focusing a beam on the CD, which is reflected back to a sensor. The sensor detects changes in the beam, and interprets these changes to read the data. This data is output as sound using a digital-to-analog converter (DAC).

A subcode in an audio CD contains information on the total number of audio tracks, the running time on the CD, running time of each track, and other information. This information allows the drive motor to speed up or slow down as needed to read data at a constant rate.

Interface

The interface of a CD player does not vary widely from manufacturer to manufacturer. It is usually composed of a few buttons and a display device. Common buttons include play, pause, stop, advance/fast forward, back/rewind and, in the case of a multiple-CD player, disk selection. The display may provide information such as track number, track time, disk number in the case of multiple-CD changers and CD-Text.

CD changer

A CD changer holds multiple Compact Discs, usually in a cartridge, and allows the user to access (or play) any of them, one at a time. CD changers are commonly found in home cinema systems, cars, and less often in computer equipment.

Prior art

Prior to real CD changers being introduced, an attempt was made to copy the double cassette players found in many audio systems. As a result, devices with two separate, fully functional CD players were made. Very few cassette changers were produced, mainly because a double-cassette deck could copy from one cassette to another. Double-CD decks, on the other hand, did not have this copy functionality since recordable CDs were not commercially available. Therefore, the shift to changers was swift, removing the need for double CD players.

Main types of CD changers

External cartridge

External cartridge for 6 CDs installed in the boot (trunk) of a car.

External cartridge CD changers have one or more cartridges that the user loads with up to 12 different CDs (depending on manufacturer) and then inserts into the CD changer. The CD changer can then remove one CD at a time for playing. This type of player is commonly found in vehicles because the user can switch easily between large amounts of media contained in different cartridges.

Internal cartridge

Internal cartridge for 5 CDs (external view)

Internal cartridge CD changers work on the same basic principle as external cartridge players, except the cartridge never leaves the CD player. This type of CD player accepts multiple CDs through a single slot and stores them internally.

Carousel

Carousel for 3 CDs

A carousel type CD changer consists of a circular platter that holds three or more CDs. Traditional carousel CD players hold three, five, or seven discs on a flat carousel tray. The carousel ejects to allow access to the CDs. Once back inside, the CD changer can rotate the carousel to access all of the CDs. Such carousel CD changers often allow the user to rotate the carousel while open, and change all CDs if no CDs are currently playing, or to eject the carousel while one CD is playing to change any CDs accessible from that position. Another type of carousel CD player is the mega-disc or "jukebox" CD players as they are also known. They usually hold anywhere from 50 to 300 discs. The mega-disc CD player holds its discs in a vertical position in slots that located 360 degrees around the carousel. When a disc is selected to be played, the carousel rotates so that the disc can be picked up by a pickup mechanism and placed in CD playback unit. Mega-disc CD players generally have a means of entering in titles of the CDs stored inside them, such as telephone style letter input system found on the remote control, a full letter keypad on the unit, or by use of an external keyboard attached to the unit. Many units can also automatically obtain the title of a CDs if it contains CD-Text info stored on it.

Evolution

Digital audio players have surpassed the concept of CD changers. For example, the first generation iPod can hold an equivalent of 50 discs (1000 songs)^[9] with a 128k bit rate for each song; thereby, the iPod is 1/10 the size of a CD changer cartridge, and about 1/20 the size of a carousel changer. Solid state flash-based digital audio players have rendered compact discs and thus CD changers obsolete for some purposes. While digital audio players often use a lossy compression scheme, they usually can accept lossless formats such as WAV (PCM) as well, matching the quality of CD audio.

Computer-based changers

CD-ROM changers existed in the early 1990s as an expensive external drive, often connecting through the SCSI interface. The changer concept is seen on the computer as one drive letter for each corresponding disc number. The computer refers to the disc by its drive letter, and the changer machine loads the disc transparently.

Changers are often used by enterprises hosting software (e.g., Encarta Encyclopedia, library software) on a server, at a time when the mean hard drive capacity was measured in hundreds of megabytes. The changer has been supplanted by exponential growth of hard drive storage densities, enabling several CD's worth of data to be stored on the drive and replacing the changer for such purposes.

See also

Wikimedia Commons has media related to: CD players

• Compact Cassette
• Compact Disc
• Hi-Fi
• High-end audio
• Jukebox
• MP3 CD
• Optical disc drive
• Radio cassette
• Radio receiver, includes information about Radio CD/DVD.
• Record changer
• Transport (recording)

References

1. ^ "CDP-101 The first Compact Disc Audio CD Player from 1982". 2007. http://www.cedmagic.com/history/sony-cdp-101.html. Retrieved 2007-02-05. 
2. ^ "Sony History". 2007. http://www.sony.net/Fun/SH/1-20/h5.html. Retrieved 2007-02-05. 
3. ^ "Luxman DX-104 CD Player". 2007. http://www.thevintageknob.org/DAD/DX104/DX104.html. Retrieved 2007-02-17. 
4. ^ "Panasonic History - Innovative Products - 1982 - CD Player". 2007. http://panasonic.net/history/corporate/products/inp1982.html. Retrieved 2007-02-05. 
5. ^ :0 "Meridian CD History". 2007. http://www.meridian-audio.com/p_cd_history.htm :0. Retrieved 2007-02-05. 
6. ^ "Luxman D-500X (in Japanese)". 2007. http://k-nisi.hp.infoseek.co.jp/d-500-xs.html. Retrieved 2007-02-05. 
7. ^ "Denon Museum - Model History - 1993 - DP-S1 (in Japanese)". 2007. http://denon.jp/museum/products/dps1.html. Retrieved 2007-02-05. 
8. ^ Swing-arm mechanism description
9. ^ Apple Presents iPod

External links

• The Audio Circuit A complete list of all brands who've developed CD-players
• "How CDs Work" at Howstuffworks.com
• Technical Information about CD players
• Info on mega-disc CD players
• Disassembly Photographs of a CD Player
• Swing-arm pickup mechanism

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)