Compact Disc player

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Image:Cd-player-explained.jpg Image:Vintagedenon.jpg A Compact Disc player (often written as compact disc player), or CD player, is an electronic device which 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. Many CD players support other formats in addition to CDs, such as DVD, CD-ROMs with audio files, and video CDs. DJs often use pitchable CD players, which have an adjustable playback sampling rate; however, the same technique can be exploited with cheaper filters used in-line with MP3 players.

1 Physical description
2 Function
3 Interface
4 CD changer
5 See also
6 References

[edit] Physical description

Most home CD players are contained in a plastic casing, which also houses the electrical system and the user interface. The plastic casing can be manufactured in many colors and textures and the overall shape may be square or rectangular, with sharp or rounded corners, or a mixture of both.

CD players designed for car audio systems or computers generally have a front casing and exposed sides and back, as these parts will be covered by the car or computer. The front casing is generally flat and, like other CD players, available in a variety of colors and textures.

The housing of a portable CD player will also contain 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.

[edit] Function

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. The laser reads information by focusing a beam on the CD, which is reflected back to 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.

[edit] Interface

The user interface of a CD player can vary widely from manufacturer to manufacturer. However, some common components are various buttons, knobs, and a display device. Common buttons include play, pause, stop, advance/fast forward, back/rewind, and in the case of a multiple-CD player, CD selection. Knobs allow control of volume, balance, and, if the player includes a radio tuner, radio station. The screen can contain a wide variety of information, but common data are track number and track time, and in the case of multiple-CD changers, CD number.

[edit] 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.

[edit] 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. Double-cassette decks were never replaced with a cassette changer, 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.

[edit] Main types of CD changers

[edit] External cartridge

Image:Cd changer external cartridge.jpg

External cartridge CD changers have one or more cartridges that the user loads (typically with 5 to 10 CDs) 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 convenient because the user typically owns at least two cartridges and therefore can load a second one to quickly switch with the first one.

[edit] Internal cartridge

Image:Cd changer internal cartridge.jpg

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.

[edit] Carousel

Image:Cd changer carousel.jpg

A carousel type CD changer consists of a circular platter that holds three to seven CDs. 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. Most carousel CD changers will 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.

[edit] Evolution

Digital audio players have surpassed the concept of CD changers. For example, the first generation iPod can hold an equivalent of 5 discs with a 128k sample 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. However, most forms of digital music use a lossy compression scheme and therefore are unacceptable for professional applications and other demanding users.

[edit] Computer-based changers

Image:Cd-player.jpg As file format size shrinks, the same capacity discs may be sufficient for growing needs of storage. However, the amount of storage space needed may be growing faster than current compression abilities can handle. As a result, newer disc formats have been created, such as DVD-ROM/DVD+/-R, DVD-RAM, Blu-Ray, HD DVD, and holographic discs.

As consumer needs extend to the point where the cost of individual drives are prohibitive, CD changers can again become useful. Unfortunately, most disc changers are still intended primarily for large enterprises with unlimited budgets.