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A Compact Disc player (often written as '''compact disc player'''), or '''CD player''', is an electronic device which plays audio Compact Disc s. CD players are often installed into home Stereo systems, Car Audio systems, and Personal Computer s. They are also manufactured as portable devices. Modern units support other formats in addition to CDs; such as DVD s, CD-ROM s with audio files and Video CD s. DJ s often use players with adjustable playback sampling rate to alter the Pitch of the music programme. Many modern CD players also include the capability to play MP3 CD 's. CD Playback functionality is also available on all modern CD-ROM/DVD-ROM drive equipped computers as well as on DVD players and CD-ROM/DVD-ROM based Game Console s. PHYSICAL DESCRIPTION CD deck. This particular model was considered top-of-the-line for its time]] Most home CD players are contained in a Plastic Casing , which also houses the electrical system and the User Interface . 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 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 Vertical Loading Top Loading .]] Tray Load with Sliding Mechanism Meridian s 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. FUNCTION CD player anatomy.]] 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 . 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. INTERFACE The interface of a CD player does not vary widely from manufacturer to manufacturer. It is usually comprised 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 Disc s, 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 CD changers have one or more Cartridge s that the user loads with up to 10 different 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 commonly found in vehicles because the user can switch easily between large amounts of media contained in different cartridges. Internal cartridge 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 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. The hold anywhere from 50 to 300 discs. The mega-disc CD player holds it's 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 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 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 large budgets. SEE ALSO
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