CD player
A CD player is an electronic device that plays audio
Modern units can play audio formats other than the original CD
History
American inventor James T. Russell is known for inventing the first system to record digital video information on an optical transparent foil that is lit from behind by a high-power halogen lamp.[1][2] Russell's patent application was first filed in 1966, and he was granted a patent in 1970. Following litigation, Sony and Philips licensed Russell's recording patents (then held by a Canadian company, Optical Recording Corp.) in the 1980s.[3][4][5]
The compact disc is not based on Russell's invention, it is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Prototypes were developed by Philips and Sony independently in the late 1970s.[6] In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984.[7] The success of the compact disc has been credited to the cooperation between Philips and Sony, who came together to agree upon and develop compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, and allowed the CD to dominate the at-home music market unchallenged.[8]
The Sony CDP-101, released in 1982, was the world's first commercially released compact disc player. It was originally sold only in Japan.[9]
Unlike early
Digital audio laser-disc prototypes
In 1974, Lou Ottens, director of the audio division of Philips, started a small group with the aim to develop an analog[12] optical audio disc with a diameter of 20 cm (7.9 in) and a sound quality superior to that of the vinyl record.[13] However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974.[12] In 1977, Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips's prototype compact disc was set at 11.5 cm (4.5 in), the diagonal of an audio cassette.[12][14]
Collaboration and standardization
Sony executive Norio Ohga, later CEO and chairman of Sony, and Heitaro Nakajima were convinced of the format's commercial potential and pushed further development despite widespread skepticism.[19] As a result, in 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink[20] and Toshitada Doi, the research pushed forward laser and optical disc technology.[17] After a year of experimentation and discussion, the task force produced the Red Book CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996.
Philips coined the term compact disc in line with another audio product, the
First Red Book CDs and players
Red Book was the first standard in the Rainbow Books series of standards.
Philips established the Polydor Pressing Operations plant in
- The first test pressing was of a recording of Richard Strauss's Eine Alpensinfonie (An Alpine Symphony) played by the Berlin Philharmonic and conducted by Herbert von Karajan, who had been enlisted as an ambassador for the format in 1979.[24]
- The first public demonstration was on the BBC television program Tomorrow's World in 1981, when the Bee Gees' album Living Eyes (1981) was played.[25]
- The first commercial compact disc was produced on 17 August 1982. It was a recording from 1979 of Claudio Arrau performing Chopin waltzes (Philips 400 025-2). Arrau was invited to the Langenhagen plant to press the start button.
- The first popular music CD produced at the new factory was The Visitors (1981) by ABBA.[26]
- The first 50 titles were released in Japan on 1 October 1982, with the first-cataloged CD in this wave being a reissue of Billy Joel's 52nd Street.[27]
The Japanese launch was followed in March 1983 by the introduction of CD players and discs to Europe
Further development and decline
The CD was planned to be the successor of the
By the early 2000s, the CD player had largely replaced the
Some CD players incorporate disc changers. Commonly these can hold 3, 5, 6, or 10 discs at once and change from one disc to the next without user intervention. Disc changers capable of holding up to 400 discs at once were available. Also, the user can manually choose the disc to be played, making it similar to a jukebox. They were often built into car audio and home stereo systems, although 7 disc CD changers were once made by NEC and Nakamichi[36] for PCs. Some could also play DVD and Blu-ray discs.
Meanwhile, with the advent and popularity of
Inner workings
The process of playing an audio CD, touted as a digital audio storage medium, starts with the plastic polycarbonate compact disc, a medium that contains the digitally encoded data. The disc is placed in a tray that either opens up (as with portable CD players) or slides out (the norm with in-home CD players, computer disc drives and game consoles). In some systems, the user slides the disc into a slot (e.g., car stereo CD players). Once the disc is loaded into the tray, the data is read out by a mechanism that scans the circular data tracks using a laser beam. An electric motor spins the disc. The tracking control is done by analog servo amplifiers and then the high-frequency analog signal read from the disc is digitized, processed and decoded into analog audio and digital control data which is used by the player to position the playback mechanism on the correct track, do the skip and seek functions and display track, time, index and, on newer players in the 2010s, display title and artist information on a display placed in the front panel.[41]
Analog signal recovery from the disc
To read the data from the disc, a laser beam shines on the surface of the disc. Surface differences between discs being played, and tiny position differences once loaded, are handled by using a movable lens with a very close focal length to focus the light on the disc. A low-mass lens coupled to an electromagnetic coil is in charge of keeping focused the beam on the 600
When the player tries to read from a stop, it first does a focus seek program that moves the lens up and down from the surface of the disc until a reflection is detected; when there is a reflection, the servo electronics lock in place keeping the lens in perfect focus while the disc rotates and changes its relative height from the optical block.
Different brands and models of optical assemblies use different methods of focus detection. On most players, the focus position detection is made using the difference in the current output of a block of four photodiodes. The photodiode block and the optics are arranged in such a way that a perfect focus projects a circular pattern on the block while a far or near focus projects an ellipse differing in the position of the long edge in north–south or west-southwest. That difference is the information that the servo amplifier uses to keep the lens at the proper reading distance during the playback operation, even if the disc is warped.[42]
Another servo mechanism in the player is in charge of keeping the focused beam centered on the data track.
Two optical pick-up designs exist, the original CDM series from Philips use a magnetic actuator mounted on a swing-arm to do coarse and fine tracking. Using only one laser beam and the 4 photodiode block, the servo knows if the track is centered by measuring side-by-side movement of the light of beam hitting on the block and corrects to keep the light on the center.
The other design by Sony uses a diffraction grating to part the laser light into one main beam and two sub-beams. When focused, the two peripheral beams cover the border of the adjacent tracks a few micrometers apart from the main beam and reflect back on two photodiodes separated from the main block of four. The servo detects the RF signal being received on the peripheral receivers and the difference in output between these two diodes conform the tracking error signal that the system uses to keep the optics in the proper track. The tracking signal is fed to two systems, one integrated in the focus lens assembly can do fine tracking correction and the other system can move the entire optical assembly side by side to do coarse track jumps.
The sum of the output from the four photodiodes makes the RF or high-frequency signal which is an electronic mirror of the pits and lands recorded on the disc. The RF signal, when observed on an oscilloscope, has a characteristic eye pattern and its usefulness in servicing the machine is paramount for detecting and diagnosing problems, and calibrating CD players for operation.
Digital signal processing
The first stage in the processing chain for the analog RF signal (from the photoreceptor device) is digitizing it. Using various circuits like a simple comparator or a data slicer, the analog signal becomes a chain of two binary digital values, 1 and 0. This signal carries all the information in a CD and is modulated using a system called
After demodulating, a CIRC error corrector takes each audio data frame, stores it in a
The Redbook standard dictates that, if there is invalid, erroneous or missing audio data, it cannot be output to the speakers as digital noise, it has to be muted.
Player control
The Audio CD format requires every player to have enough processing power to decode the CD data; this is normally made by application-specific integrated circuits (ASICs). ASICs do not work by themselves, however; they require a main microcomputer or microcontroller to orchestrate the entire machine. The firmware of basic CD players typically is a real-time operating system.
Some early optical computer drives are equipped with an audio connector and buttons for standalone CD playback functionality.[43]
Tray design types
Tray loading
. However, there have been some notable exceptions to this common CD tray design.Vertical loading
During the launch of the first prototype Goronta CD player
Top loading
In 1983
Top-loading was adopted on various equipment designs such as mini systems and portable CD players, but among stereo component CD players, only a handful of top-loading models have been made. Examples include Luxman's D-500 and D-500X series[53] players and Denon's DP-S1,[54] both launched in 1993. Top-loading is also common in players intended for broadcast and live sound DJ use, such as Technics' SL-P50 (1984–1985) and Technics SL-P1200 (1986–1992). They more closely mimic the physical arrangement and ergonomics of record turntables used in those applications.
The top-loading disc tray design is also used in most
Tray loading with sliding mechanism
The Philips CD303 of 1983-1984 was the first player to adopt tray loading with a 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
Slot loading
Slot loading is the preferred loading mechanism for car audio players. There is no tray that pops out, and a motor is used to assist disc insertion and removal. Some slot-loading mechanisms and changers can load and play back
Pickup mechanisms
Two types of optical tracking mechanisms exist:
- The swing-arm mechanism, originally designed by Philips[55] – 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 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.[57]
Mechanical components
A CD player has three major mechanical components: a drive motor, a
A TOC or Table of Contents is located after the lead-in area of the disc, which is located in an inner ring of the disc, and contains roughly five kilobytes of available space. It is the first information that the player reads when the disc is loaded in the player and contains information on the total number of audio tracks, the running time on the CD, the running time of each track, and other information such as ISRC and the format structure of the disc. The TOC is of such vital importance for the disc that if it is not read correctly by the player, the CD could not be played back. That is why it is repeated 3 times before the first music program starts. The lead out area in the end (the outer peripheral) of the disc tells the player that disc has come to an end.
CD player features
CD players can employ a number of ways to improve performance or reduce component count or price. Features such as oversampling, one-bit DACs, dual DACs, interpolation (error correction), anti-skip buffering, digital and optical outputs are, or were, likely to be found. Other features improve functionality, such as track programming, random play and repeat, or direct track access. Yet others are related to the CD player's intended target, such as anti-skip for car and portable CD players, pitch control and queuing for a DJ's CD player, remote and system integration for household players. Description of some features follows:
- Oversampling is a way to improve the performance of the low pass filter present at the output of most CD players. By using a higher sampling frequency, a multiple of the 44.1 kHz used by CD encoding, it can employ a filter with much lower requirements.
- One-bit DACs were less expensive than other types of DACs, while providing similar performance.
- Dual DACs were sometimes advertised as a feature because some of the early CD players used a single DAC, and switched it between channels. This required additional supporting circuits, possibly degrading sound quality.
- Anti-skip or Antishock, is a way for the CD player to avoid interrupting the audio output when mechanical shock is experienced by the disc playback mechanism. It consists of an additional data processor and a memory bufferfor later decoding. Some players may compress the audio data prior to buffering to use lower capacity (and less expensive) RAM chips. Typical players can store about 44 seconds of audio data on a 16 Mbit RAM chip.
Portable CD players
Small portable players
A
In 1998, portable
Boomboxes
A
Most boomboxes from the 2010s typically include a CD player compatible with
DJ equipment
DJs who are performing
See also
- Compact Cassette
- High-end audio
- Jukebox
- List of compact disc player manufacturers
- MP3 CD
- Optical disc drive
- Radio cassette
- Radio receiver, includes information about Radio CD/DVD.
- Record changer
- Transport (recording)
References
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An international collaboration between Philips and the Sony Corporation lead to the creation of the compact disc. The author explains how it came about
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External links
- The Inner Workings of CD/DVD Drives WeCanFigureThisOut.org
- The Audio Circuit Archived 2013-10-06 at the Wayback Machine — a complete list of CD-player brands
- Technical information about CD players
- Mega-disc CD players