page_title: CD player
section_title: Pickup mechanisms
hierarchical_section_title: CD player / Pickup mechanisms
caption_attribution_description: English: Underside of the optical deck of a common portable CD player. Shows the spindle motor, top center; screw drive and motor, right center; and at center the underside of the optical pickup (which holds laser diode assembly).
context_page_description: A CD player is an electronic device that plays audio compact discs, which are a digital optical disc data storage format. CD players were first sold to consumers in 1982. CDs typically contain recordings of audio material such as music or audiobooks. CD players may be part of home stereo systems, car audio systems, personal computers, or portable CD players such as CD boomboxes. Most CD players produce an output signal via a headphone jack or RCA jacks. To use a CD player in a home stereo system, the user connects an RCA cable from the RCA jacks to a hi-fi and loudspeakers for listening to music. To listen to music using a CD player with a headphone output jack, the user plugs headphones or earphones into the headphone jack.
  Modern units can play audio formats other than the original CD PCM audio coding, such as MP3, AAC and WMA. DJs playing dance music at clubs often use specialized players with an adjustable playback speed to alter the pitch and tempo of the music. Audio engineers using CD players to play music for an event through a sound reinforcement system use professional audio-grade CD players.
context_section_description: Two types of optical tracking mechanisms exist:
  The swing-arm mechanism, originally designed by Philips – the lens moves at the end of an arm, in a manner similar to the tone arm assembly of a record player. Used in earliest Philips CD players and later replaced with cheaper radial mechanisms.
  The radial mechanism, designed by Sony, which is the one used in most CD players in the 2000s – the lens moves on a radial rail being driven by a rotating gear from a motor or a linear magnetic assembly. The motor or linear magnetic assembly consists of a solenoid mounted to the moving laser assembly, wound over a permanent magnetic field attached to the base of the mechanism. It is also known as three-beam linear tracking.
  The swing-arm mechanism has a distinctive advantage over the other in that it does not "skip" when the rail becomes dirty. The swing arm mechanisms tend to have a much longer life than their radial counterparts. The main difference between the two mechanisms is the way they read the data from the disc. The swing-arm mechanism uses a magnetic coil wound over a permanent magnet to provide the tracking movement to the laser assembly in a similar way a hard drive moves its head across the data tracks. It also uses another magnetic movement mechanism attached to the focusing lens to focus the laser beam on the disc surface. By operating the tracking or the focus actuators, the laser beam can be positioned on any part of the disc.
  This mechanism employs a single laser beam and a set of four photodiodes to read, focus and keep track of the data coming from the disc.
  The linear tracking mechanism uses a motor and reduction gears to move the laser assembly radially across the tracks of the disc and it also has a set of six coils mounted in the focusing lens over a permanent magnetic field. One set of two coils moves the lens closer to the disc surface, providing the focusing motion, and the other set of coils moves the lens radially, providing a finer tracking motion. This mechanism uses the three-beam tracking method in which a main laser beam is used to read and focus the data track of the disc using three or four photodiodes, depending on the focus method, and two smaller beams read the adjacent tracks at each side to help the servo keep the tracking using two more "helper" photodiodes.
caption: Underside view showing a radial-type tracking mechanism with screw drive
exif: {"Image Make": "NIKON CORPORATION", "Image Model": "NIKON D40", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "GIMP 2.4.6", "Image DateTime": "2009:01:25 19:04:03", "Image YCbCrPositioning": "Centered", "Image ExifOffset": "210", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "570", "Thumbnail JPEGInterchangeFormatLength": "7900", "Thumbnail YCbCrPositioning": "Centered", "EXIF ExposureTime": "15", "EXIF FNumber": "16", "EXIF ExposureProgram": "Manual", "EXIF ISOSpeedRatings": "200", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2009:01:20 19:20:30", "EXIF DateTimeDigitized": "2009:01:20 19:20:14", "EXIF ExposureBiasValue": "-2/3", "EXIF MaxApertureValue": "5", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire", "EXIF FocalLength": "55", "EXIF SensingMethod": "One-chip color area"}