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A portable CD player

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 (or other amplifier) 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. CD playback functionality is also available on CD-ROM/DVD-ROM drive-equipped computers as well as on DVD players and most optical disc-based home video game consoles.

History

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Sony CDP-101 from 1982, the first commercially released CD player for consumers
Philips CD100 from 1983, the first commercially released CD player in the USA and Europe

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 LaserDisc players, first CD players already used laser diodes instead of larger helium-neon lasers.[10][11]

Digital audio laser-disc prototypes

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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]

Heitaro Nakajima, who developed an early digital audio recorder within Japan's national public broadcasting organization NHK in 1970, became general manager of Sony's audio department in 1971. His team developed a digital PCM adaptor audio tape recorder using a Betamax video recorder in 1973. After this, in 1974, the leap to storing digital audio on an optical disc was easily made.[15] Sony first publicly demonstrated an optical digital audio disc in September 1976. A year later, in September 1977, Sony showed the press a 30 cm (12 in) disc that could play 60 minutes of digital audio (44,100 Hz sampling rate and 16-bit resolution) using MFM modulation.[16] In September 1978, the company demonstrated an optical digital audio disc with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, and cross-interleaved error correction code—specifications similar to those later settled upon for the standard compact disc format in 1980. Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels.[16] Sony's AES technical paper was published on 1 March 1979. A week later, on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc"[17] in Eindhoven, Netherlands.[18]

Collaboration and standardization

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This disc is highly corroded. The error correction cannot correct all errors. Two minutes can be played, however.

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 Compact Cassette,[14] and contributed the general manufacturing process, based on video LaserDisc technology. Philips also contributed eight-to-fourteen modulation (EFM), which offers a certain resilience to defects such as scratches and fingerprints, while Sony contributed the error-correction method, cross-interleaved Reed–Solomon coding (CIRC). The Compact Disc Story,[12] told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The task force consisted of around four to eight persons,[21][22] though according to Philips, the compact disc was "invented collectively by a large group of people working as a team."[23]

First Red Book CDs and players

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Red Book was the first standard in the Rainbow Books series of standards.

Philips established the Polydor Pressing Operations plant in Langenhagen near Hannover, Germany, and quickly passed a series of milestones.

The Japanese launch was followed in March 1983 by the introduction of CD players and discs to Europe[28] and North America (where CBS Records released 16 titles).[29] This event is often seen[by whom?] as the "Big Bang" of the digital audio revolution. The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities, and its handling quality received particular praise. As the price of players gradually came down, and with the introduction of the portable Walkman, the CD began to gain popularity in the larger popular and rock music markets. The first artist to sell a million copies on CD was Dire Straits, with their 1985 album Brothers in Arms.[30] The first major artist to have his entire catalog converted to CD was David Bowie, whose 15 studio albums were made available by RCA Records in February 1985, along with four greatest hits albums.[31] In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.[32]

Sony CD Walkman D-E330

Further development and decline

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A JVC FS-SD5R CD player from the 1990s with a transparent plastic cover and blue backlight

The CD was planned to be the successor of the gramophone record for playing music, rather than primarily as a data storage medium, but from its origins as a format for music, its use has grown to encompass other applications. In 1983, following the CD's introduction, Immink and Braat presented the first experiments with erasable compact discs during the 73rd AES Convention.[33] In June 1985, the computer-readable CD-ROM (read-only memory) was introduced and, in 1990, the CD-Recordable, also developed by both Sony and Philips.[34] Recordable CDs were a new alternative to tape for recording music and copying music albums without the defects introduced in the compression used in other digital recording methods. Other newer video formats such as DVD and Blu-ray use the same physical geometry as CD, and most DVD and Blu-ray players are backward compatible with audio CD.

By the early 2000s, the CD player had largely replaced the audio cassette player as standard equipment in new automobiles, with 2010 being the final model year for any car in the US to have a factory-equipped cassette player.[35] Currently, with the increasing popularity of portable digital audio players, such as mobile phones, and solid state music storage, CD players are being phased out of automobiles in favor of minijack auxiliary inputs and connections to USB devices.[citation needed]

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 Internet-based distribution of files in lossily-compressed audio formats such as MP3, sales of CDs began to decline in the 2000s. For example, between 2000 and 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%[37] – although independent and DIY music sales may be tracking better (according to figures released 30 March 2009), and CDs still continue to sell greatly.[38] As of 2012, CDs and DVDs made up only 34% of music sales in the United States.[39] In Japan, however, over 80% of music was bought on CDs and other physical formats as of 2015.[40] As of 2020, compact cassettes, vinyl records, and CDs are still being released by some musicians, primarily as merchandise, to allow fans to provide financial support while receiving something tangible in return.

Inner workings

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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

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Photodiode array on the Philips RAFOC single-beam tracking optical device used in many CDM optical assemblies
Movable lens with coils

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 nm wide data track.

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

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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 eight-to-fourteen modulation (EFM). The second stage is demodulating the EFM signal into a data frame that contains the audio samples, error correction parity bits, according with the CIRC error correction code, and control data for the player display and micro-computer. The EFM demodulator also decodes part of the CD signal and routes it to the proper circuits, separating audio, parity and control (subcode) data.

After demodulating, a CIRC error corrector takes each audio data frame, stores it in memory and verifies that it has been read correctly, if it is not, it takes the parity and correction bits and fixes the data, then it moves it out to a digital-to-analog converter (DAC) to be converted to an analog audio signal. If the data missing is enough to make recovery impossible, the correction is made by interpolating the data from subsequent frames so the missing part is not noticed. Each player has a different interpolation ability. If too many data frames are missing or unrecoverable, the audio signal may be impossible to fix by interpolation, so an audio mute flag is raised to mute the DAC to avoid played back of invalid data. 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

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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

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Tray loading

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A 1980s-era Denon CD player with the chassis cover removed to show the electronic and mechanical components.
An example of a Pioneer CD player's tray closing.

Sony released its CDP-101 CD player[44] in 1982 with a slide-out tray design for the CD. As it was easy to manufacture and to use, most CD player manufacturers stayed with the tray style ever since.[45][46] The tray mechanism is also used in many modern desktop computer cases, as well as the Philips CD-i, PlayStation 2, Xbox and Xbox 360. However, there have been some notable exceptions to this common CD tray design.

Vertical loading

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During the launch of the first prototype Goronta CD player[47] by Sony at the Japanese Audio Fair in 1982, Sony showcased the vertical loading design. Although the Sony prototype design was never put into volume production, the concept 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,[48] 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 Web site.[49] The vertical loading is similar the one common in cassette decks, where the holder opens, and disc is dropped to it. The holder is closed manually, by motor after pressing a button, or completely automatically. Some CD players combine vertical loading with slot loading due to the disc being drawn further into the disc holder as it closes.

Top loading

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Philips CD100 Player

In 1983, Philips, at the US and European launch of the CD format, showcased the first top-loading CD tray designs with their CD100 CD player.[50][51] (Philips audio products were sold as Magnavox in the US at the time.) 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. Later, Meridian introduced their MCD high end CD player,[52] with Meridian electronics in the Philips CD100 chassis.

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 fifth-generation video game consoles (PlayStation, Saturn, 3DO Interactive Multiplayer), as well as the Dreamcast, GameCube, and Wii Mini.

Tray loading with sliding mechanism

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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 Meridians 200 and 203 players were of this type. They were also the first to use a design in which the audio electronics were in a separate enclosure from the CD drive and pickup mechanism. A similar mechanism is used in slim optical disc drives (also known as slim internal DVD drive, optical drive or DVD burner), which were once commonly used in laptop computers.

Slot loading

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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 Mini CDs without the need of an adapter (such as the original Wii model's standard-sized disc slot being capable of accepting smaller GameCube Game Discs) but they may work with limited functionality (a disc changer with a Mini CD inserted will refuse to operate until such disc is removed, for example). Non-circular CDs cannot be used on such loaders because they cannot handle non-circular discs. When inserted, such discs may become stuck and damage the mechanism. It is also used on some laptop computers, the original and slim PlayStation 3, the Wii's original model and its Family Edition and most eighth-generation video game consoles (the Wii U, PlayStation 4 and Xbox One), as well as the ninth-generation PlayStation 5 and Xbox Series X.

Pickup mechanisms

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Underside view showing a radial-type tracking mechanism with screw drive
Philips swing arm optical mechanism
The optical chip extracted from a CD player. The three dark rectangles are photosensitive, read the data from the disk and keep the beam focused. Electronic tracking, aided with the two photodiodes at the sides, keeps the laser beam centered on the middle of the data track.

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.
Philips one-beam laser assembly

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.[citation needed] 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.[56]

Sharp laser optical assembly. All six focusing and tracking coils can be seen.

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

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Philips Portable CD player disassembled

A CD player has three major mechanical components: a drive motor, a lens system or pickup head, and a tracking mechanism. The drive motor (also called spindle) spins the disc to a scanning velocity of 1.2–1.4 m/s (constant linear velocity) – equivalent to approximately 500 RPM at the inside of the disc, and approximately 200 RPM at the outside edge. (A disc played from beginning to end slows its rotation rate during playback.) The tracking mechanism moves the lens system along the spiral tracks in which information is encoded, and the lens assembly reads the information using a laser beam produced by a laser diode. The laser reads information by focusing a beam on the CD, which is reflected off the disc's mirrored surface back to a photodiode array sensor. The sensor detects changes in the beam, and a digital processing chain interprets these changes as binary data. The data are processed and eventually converted to sound using a DAC.

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 three 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

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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, Antishock, or electronic skip protection 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 RAM chip installed on the player that reads the disc at double speed and stores various frames of audio data in a RAM memory buffer for 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

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Small portable players

[edit]
An early portable player, a Sony Discman model D-121

A portable CD player is a portable audio player used to play compact discs. Portable CD players are powered by batteries and they have a 1/8" headphone jack into which the user plugs a pair of headphones. The first portable CD player released was the D-50 by Sony.[58] The D-50 was made available on the market in 1984,[59] and adopted for Sony's entire portable CD player line.

In 1998, portable MP3 players began to compete with portable CD players. After Apple Computer entered the music player market with its iPod line, within ten years it became the dominant seller of portable digital audio players, "...while former giant Sony (maker of the [portable] Walkman and [CD] Discman [was] struggling."[60] This market shift was initiated when the first portable digital audio player, the Rio digital music player, was introduced. The 64 MB Rio MP3 player enabled users to store about 20 songs.[61] One of the benefits of the Rio over portable CD players was that since the Rio had no moving parts, it offered skip-free playback.[61] Since 1998, the price of portable digital audio players has dropped and the storage capacity has increased significantly. In the 2000s, users can "carry [their] entire music collection in a [digital audio] player the size of a cigarette package."[61] The 4 GB iPod, for example, holds over 1,000 songs.[61] By the early 2010s, MP3 players began to decline in popularity,[62] in favour of downloading music on platforms such as iTunes, and later streaming music on platforms such as Spotify, Apple Music, and YouTube Music.[63][64][65]

Boomboxes

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A Sony CD boombox from 2005

A boombox is a common term for a portable cassette and AM/FM radio that consists of an amplifier, two or more loudspeakers and a carrying handle. Beginning in the 1990s, boomboxes typically included a CD player. The boombox CD player is the only type of CD player that produces sound audible by the listener independently, without the need for headphones or an additional amplifier or speaker system. Designed for portability, boomboxes can be powered by batteries as well as by line current. The boombox was introduced to the American market during the mid-1970s. The desire for louder and heavier bass led to bigger and heavier boxes; by the 1980s, some boomboxes had reached the size of a suitcase. Most boomboxes were battery-operated, leading to extremely heavy, bulky boxes.[66]

Most boomboxes from the 2010s typically include a CD player compatible with CD-R and CD-RW, which allows the user to carry their own music compilations on a higher fidelity medium. Many also permit iPod and similar devices to be plugged into them through one or more auxiliary input jacks. Some also support formats such as MP3 and WMA. Another modern variant is a DVD player/boombox with a top-loading CD/DVD drive and an LCD video screen in the position once occupied by a cassette deck.[67] Many models of this type of boombox include inputs for external video (such as television broadcasts) and outputs to connect the DVD player to a full-sized television.

DJ equipment

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This example of a CD player used by DJs is the Denon DN-2500 dual CD player, on the right side of the picture. A Behringer VMX-200 DJ mixer is also shown in the left side, in the foreground.

Disc jockeys (DJs) who are playing a mix of songs at a dance club, rave, or nightclub create their dance mixes by having songs playing on two or more sound sources and using a DJ mixer to transition seamlessly between songs. In the 1970s disco era, DJs typically used two record players.[68] From the 1980s to the 1990s, two compact cassette players became a popular sound source for DJs.[69] In subsequent decades, DJs shifted to CDs and then to digital audio players. DJs who use CDs and CD players typically use specialized DJ CD players (such as CDJs) that have features not available on regular CD players, such as pitch control.

DJs who are performing scratching–the creation of rhythmic sounds and sound effects from sound recordings–traditionally used vinyl records and turntables. In the 2010s, some specialized DJ CD players can be used to create scratching effects using songs on CDs.

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

CD player

View on Grokipedia
from Grokipedia
A CD player is an electronic device designed to reproduce audio from compact discs (CDs), which are media containing digitally encoded sound data in the form of pits and lands on a substrate. It uses a low-powered beam to read the data by detecting variations in light reflection, converts the digital signals via (PCM) into analog audio, and outputs the sound through speakers or , typically supporting playback with . Standard CDs measure 12 cm in diameter and can store up to 74 minutes of uncompressed audio, sampled at 44.1 kHz with 16-bit resolution, enabling superior sound quality compared to analog formats like vinyl records or cassette tapes. The development of the CD player stemmed from ' initiative in the mid-1970s to create a durable, high-quality alternative to records, led by engineer and his team, building on earlier technology before shifting to . In 1979, partnered with to standardize the format, culminating in the "Red Book" specification (IEC 60908) that defined the CD-digital audio system, including error correction via cross-interleaved Reed-Solomon coding (CIRC) and (EFM) for reliable data retrieval. The first commercial CD player, 's CDP-101, was released on October 1, 1982, in , priced at 168,000 yen, and quickly gained traction worldwide, revolutionizing by offering skip-resistant playback and precise track access. Over the and , CD players evolved from bulky, expensive components integrated into stereo systems to compact, portable models like Sony's D-50 in 1984, which incorporated one-chip LSI circuits and miniaturized optical pickups for on-the-go use. This innovation spurred the music industry's shift to , with billions of CDs produced and players becoming ubiquitous in cars, boomboxes, and personal devices by the early 2000s. Although streaming and solid-state media have diminished their dominance, CD players remain valued for archival audio playback and applications due to their robust error-handling and uncompressed output.

History

Origins and prototypes

The development of the CD player traces its roots to early experiments in technology during the late 1960s. In 1969, Research Laboratories in initiated work on an optical video disc system, marking the beginning of practical for consumer applications. This effort evolved into the Video Long Play (VLP) prototype by 1972, an analog capable of storing 30 minutes of color video per side using a gas for playback, which served as a foundational precursor to audio-only optical storage by demonstrating non-contact reading of disc surfaces. A pivotal contribution came from American physicist James T. Russell, who while working at the Battelle Memorial Institute's , conceived a laser-based system for recording. Russell's U.S. 3,501,586, granted on March 17, 1970, described an analog-to-digital-to-optical photographic recording and playback method that converted audio signals into , recorded as microscopic light and dark spots on film using a (with spot sizes as small as 1/300 mm), and retrieved them via laser scanning for high-fidelity reproduction. This invention laid the groundwork for digital optical audio storage, though it initially targeted archival data rather than consumer playback. Independently, advanced the concept toward a practical audio . In September 1976, publicly demonstrated an early optical disc at the Tokyo Audio Fair, using a 30 cm disc with (PCM) encoding and laser readout, though it produced poor sound quality with static. By September 1977, refined the design to a 30 cm disc achieving approximately 100 minutes of playback using a 44.1 kHz sampling rate, which originated from adaptations of 's existing recorders to align audio data with video frame rates for efficient mastering, ensuring compatibility with professional studio equipment. By 1978, continued refining its , while developed an 11.5 cm disc independently. and initiated collaboration in 1979 to standardize the format. Early prototypes faced significant technical hurdles, particularly from environmental factors and mechanical precision. Dust particles and surface scratches caused audible dropouts or clicks in analog optical systems, as the shallow pits (around 0.125 micrometers deep) were highly susceptible to interference, rendering high-fidelity audio unreliable without digital intervention. Playback speed variations, due to inconsistencies in and disc rotation (initially at 1,800 rpm), introduced wow and flutter, further degrading ; these were mitigated in later digital prototypes through error correction codes and brief muting intervals under 10 ms to conceal errors imperceptibly. These challenges necessitated a shift to fully digital encoding with robust error handling by the late 1970s.

Standardization and early commercialization

In 1979, Philips and Sony initiated a collaboration to establish a unified standard for digital optical audio discs, combining ' expertise in from video disc technology with 's advancements in recording. This partnership aimed to create a consumer-friendly format that could replace vinyl records with high-fidelity, durable playback. The joint effort involved multiple technical meetings between engineers from both companies, culminating in the formalization of the (CD-DA) standard. The resulting specification, known as the Red Book, was published in 1980 by and . It defined key parameters including a 120 mm disc diameter for portability and robustness, a playback capacity of approximately 74 to 80 minutes to accommodate full symphonies like Beethoven's Ninth, and (EFM) encoding to optimize data density while minimizing errors. These elements ensured compatibility across manufacturers and set the foundation for digital audio distribution. The Red Book was adopted by the (IEC) and became the de facto industry standard. Commercialization began with the launch of the on October 1, 1982, in , marking the world's first consumer CD player. This top-loading unit featured 16-bit (PCM) for audio resolution, matching the Red Book's digital specifications, along with a servo-controlled pickup for precise disc reading. Priced at around 168,000 yen (approximately $730 USD at the time, equivalent to about $900 in later markets), it targeted audiophiles despite its high cost. Initial availability was limited, with only about 50 CD titles released simultaneously, including Billy Joel's 52nd Street as one of the inaugural albums pressed for the format.

Market expansion and technological advancements

Following its debut in the United States in , the CD player experienced rapid market expansion, with sales increasing from approximately 35,000 units in to 250,000 in 1984 and a projected 450,000 in 1985. This growth accelerated further, reaching an estimated 1 million units by 1986, establishing the CD player as one of the fastest-adopted home electronics devices of the era. Technological advancements during this period extended the CD format's capabilities beyond audio playback. In 1984, Philips and Sony initiated development of the Compact Disc-Interactive (CD-i) prototype, aimed at enabling interactive multimedia content that combined audio with text and graphics, which influenced subsequent innovations like multisession recording for incremental data addition to discs. Building on this, Philips and Sony published the CD-R (recordable) specification in 1988, allowing users to write data once to blank discs for permanent storage and playback in compatible players. Further progress came with the introduction of (rewritable) technology in 1996, standardized by and other vendors, which permitted multiple overwrite cycles on the same disc, enhancing versatility for both consumer and professional applications. CD players became seamlessly integrated into home stereo systems during the 1980s and 1990s through standard analog RCA outputs, facilitating widespread adoption in living rooms and contributing to the format's dominance. By 1999, CDs accounted for nearly 90% of U.S. revenue, reflecting their peak in audio media.

Decline and legacy

The introduction of portable MP3 players, such as Apple's in 2001, marked the beginning of a significant shift away from , enabling consumers to carry thousands of songs in a compact device and accelerating the decline of CD sales. This trend was accelerated by file-sharing services like in 1999, which enabled widespread and eroded physical sales. It intensified with the launch of streaming services like in 2008, which offered on-demand access to vast music libraries without the need for physical purchases. Global recorded music shipments peaked at approximately 2.5 billion units in 2001 (mostly CDs), while by 2020, global physical album sales had declined to around 250 million units, with CDs comprising the majority; physical formats accounted for just 5% of total music revenue by the latter year. Manufacturing of standalone consumer CD players waned in the 2010s as major producers like scaled back mass-market production in response to falling demand, shifting focus to integrated systems, professional equipment, and niche models. Despite this, dedicated markets have sustained a smaller , with high-end players emphasizing superior sound reproduction for enthusiasts who value tangible media. The CD player's legacy endures in establishing foundational digital audio standards, including 16-bit/44.1 kHz resolution, which directly influenced lossless formats like for preserving CD-quality audio without compression artifacts and paved the way for extensions beyond CD capabilities. However, the proliferation of billions of discarded CDs has raised environmental concerns, as their and aluminum composition contributes to accumulation and challenges efforts, releasing potential toxins if improperly incinerated. As of , CD players are experiencing a nostalgic revival driven by generations seeking analog-era tactility amid digital fatigue, with sales of retro-styled models rising and hybrid variants integrating CD playback with streaming and turntable functions to bridge old and new formats.

Technical principles

Optical disc reading

The optical disc reading process in a CD player relies on a semiconductor laser diode that emits infrared light at a wavelength of 780 nm to probe the data layer of the . This near-infrared beam passes through the protective layer and is directed toward the reflective aluminum surface etched with microscopic pits and lands, where pits represent depressions approximately 0.125 μm deep and lands are the flat reflective areas between them. The laser's low power output, typically a few milliwatts, ensures safe reading without damaging the disc. When the focused laser beam strikes a land, it reflects strongly back toward the optical pickup unit due to the smooth metallic surface, whereas hitting a pit causes the light to scatter or interfere destructively, resulting in reduced reflection intensity. These variations in reflected light intensity—corresponding to transitions between pits and lands—are captured by an array of photodiodes in the pickup unit, which convert the optical signals into corresponding electrical currents. The photodiodes, often arranged in a quadrant configuration, generate a high-frequency electrical signal (known as the RF signal) that encodes the binary data as 0s and 1s based on the reflection differences, with pit-land transitions marking bit boundaries. To achieve precise reading, the beam is focused by a collimating lens and an objective lens into a small spot size of approximately 1.6 μm, matching the scale of the features and the 1.6 μm track pitch. Servo s, including focus and tracking servos, continuously adjust the lens position using feedback from the signals to maintain the beam's alignment on the spiral track, compensating for disc tilt, wobble, or vibrations with actuators that move the in sub-micrometer increments. The disc rotates at a constant linear velocity (CLV) of 1.2–1.4 m/s under the spot, varying the angular speed from about 500 rpm at the inner to 200 rpm at the outer edge to sustain a consistent channel of approximately 4.32 Mbit/s for the raw RF signal. This reading process outputs the RF signal, which is subsequently processed for error correction to ensure before decoding.

Digital signal encoding and decoding

The digital encoding of audio for (CD-DA) begins with (PCM), where stereo audio signals are sampled at a rate of 44.1 kHz and quantized to 16 bits per sample, resulting in a raw bitrate of 1.411 Mbps for both channels combined. This sampling frequency was selected to capture frequencies up to 20 kHz with a Nyquist margin, while the 16-bit depth provides a of approximately 96 dB suitable for high-fidelity audio. The PCM data is organized into , each containing 24 samples per channel, or 768 bits of audio data per frame. To enhance error resilience, the PCM data undergoes encoding with the Cross-Interleaved Reed-Solomon Code (CIRC), a two-stage process that adds parity symbols and interleaves data across frames to combat burst errors from disc imperfections. In the first stage, Reed-Solomon coding over bytes adds outer parity (4 bytes per 24 data bytes), followed by inner parity (4 bytes per 28 symbols including outer parity), creating a structure that can correct burst errors up to approximately 4,000 consecutive channel bits. The interleaving then spreads data symbols across multiple frames—up to 109 frames for outer code and 4 frames for inner code—converting clustered errors into isolated ones for effective correction during playback. Each CIRC-encoded frame includes 24 audio bytes, 4 outer parity bytes, 4 inner parity bytes, and provisions for subcode data, totaling 32 symbols per frame before further modulation. The encoded data is then modulated using Eight-to-Fourteen Modulation (EFM) to prepare it for optical storage as pits and lands on the disc. EFM maps each 8-bit data symbol (from the CIRC output) to one of 256 specific 14-bit channel bit patterns, selected from 267 possible non-return-to-zero inverted (NRZI) codes that maintain a minimum run length of 3 channel bits (Tmin=3) and a maximum of 11 (Tmax=11) to ensure reliable pit/land transitions and clock recovery. Three additional merging bits are inserted between each 14-bit symbol to maintain the run-length constraints across symbol boundaries and to achieve DC balance by minimizing the digital sum variation (DSV), which suppresses low-frequency components in the read signal for better servo tracking and data detection. A frame's EFM stream, including a 24-bit sync pattern, 32 × 17 channel bits (14 data + 3 merging), and subcode integration, yields a channel bitrate of 4.3218 Mbps. During decoding in a CD player, the process reverses these steps starting from the optically read RF signal, which is digitized and synchronized using a (PLL) at 4.3218 MHz to extract the EFM channel bits. EFM demodulation employs a to convert the 14-bit symbols back to 8-bit data, removing merging bits while verifying run lengths and DSV for flagging, thus recovering the CIRC-encoded audio frames and subcode symbols. The subcodes—embedded as one byte per frame across eight channels (P through W)—are deinterleaved separately; for instance, the Q channel encodes track numbers, timings, and absolute addresses for and display. Finally, CIRC decoding deinterleaves the data using a buffer (typically 2 KB), applies Reed-Solomon correction on inner and outer codes to reconstruct the original 16-bit PCM samples, and outputs the raw audio stream at 1.411 Mbps.

Error correction and data integrity

The Cross-Interleaved Reed-Solomon Code (CIRC) serves as the core error correction mechanism in CD players, ensuring reliable from the despite surface imperfections like scratches and fingerprints. Developed jointly by and , CIRC employs two layers of Reed-Solomon codes—an inner code RS(32,28) and an outer code RS(28,24)—cross-interleaved to separate and redistribute data symbols across frames, enabling effective handling of both random and burst common in optical media. Parity symbols added during encoding allow the decoder to detect and correct by reconstructing missing or corrupted symbols, with the interleaving delaying and spacing out burst to fit within the code's correction radius. CIRC can correct burst errors up to 3,500 bits (approximately 2.5 mm track length on the disc surface), sufficient for typical fingerprints or minor surface contaminants that cause localized . CIRC can fully correct burst errors up to approximately 2.5 mm (4,000 bits) without audible degradation, using parity symbols and interleaving. For longer defects, estimates missing samples to conceal errors. For scratches up to 3.5 mm, the system relies on the parity symbols to fully correct the errors without audible degradation, as the Reed-Solomon codes support up to 2 symbol corrections in the inner layer and 4 in the outer layer after de-interleaving. This capability stems from the code's minimum distance design, where the number of parity symbols determines the error-correcting bound. For bursts exceeding full correction capacity (up to ~8.5 mm or 12,000 bits), the player uses to conceal errors by estimating values from neighboring samples, preventing audible distortions like clicks. When errors exceed direct correction, such as for larger bursts, CD players use interpolation to conceal uncorrectable symbols by estimating values from adjacent audio samples, preventing clicks or pops in playback. The decoder flags uncorrectable errors via Q-parity checks, triggering interpolation for isolated symbols or short gaps, while severe consecutive errors may prompt muting to avoid distortion. The system is designed to handle typical defects without audible artifacts through correction and concealment, with full correction up to ~2.5 mm. However, limitations arise with defects surpassing CIRC's capacity, such as deep scratches or extensive fingerprints exceeding 3.5 mm, where error bursts overwhelm the parity symbols and proves insufficient, resulting in skips, bursts, or temporary muting. In extreme cases, the player may halt playback or jump to the next accessible frame to preserve overall integrity, highlighting the system's reliance on disc condition for optimal performance.

Mechanical design

Disc loading mechanisms

Disc loading mechanisms in CD players facilitate the insertion and ejection of compact discs, enabling secure placement on the internal spindle for playback while balancing factors like user convenience, structural integrity, and environmental integration. These mechanisms evolved to address diverse applications, from stationary home systems to compact automotive units, prioritizing reliable disc handling without compromising optical reading precision. Tray loading employs a horizontal motorized drawer that extends from the player, allowing users to place the disc on a central hub before retraction secures it onto the spindle. This design, prevalent in home and stationary units, provides stability by minimizing manual handling risks and supporting multiple disc sizes through an adjustable or fixed surface. Motorized ejection ensures smooth operation, reducing wear on the disc edges. Slot loading involves inserting the disc edge-first into a narrow front slot, where rubber-coated rollers grasp and pull it inward until aligned with the spindle. Common in automotive and slim-profile players, this mechanism enhances space efficiency by eliminating protruding trays, making it ideal for integrated dashboards or portable enclosures. The rollers, driven by a dedicated motor, separate post-insertion to avoid surface contact, preserving disc integrity. Top loading features a manual or hinged on the player's upper surface, where the disc is placed directly onto an exposed spindle and secured by a clamp. Favored by audiophiles, this approach reduces mechanical intermediaries, thereby minimizing transmission to the disc during rotation and potentially improving signal . The direct spindle integration follows loading, with the clamp ensuring centered positioning without additional conveyance. Vertical loading utilizes an upright slot or oriented perpendicular to the player's base, drawing the disc into position via rollers or tabs that hold it edge-on until clamping. Employed in designs aiming to conserve horizontal desk space, such as certain compact or wall-mountable units, this configuration maintains functionality in non-horizontal orientations by relying on gravitational or spring-assisted alignment.

Spindle and motor systems

The spindle motor in a CD player is a brushless designed to rotate the at variable speeds ranging from approximately 200 RPM at the outer edge to 500 RPM at the inner edge, ensuring a constant linear velocity (CLV) of 1.2 to 1.4 m/s for consistent data readout. This CLV adjustment is achieved through a servo feedback system that monitors the recovered clock signal from the disc and dynamically varies the motor's rotational speed as the laser pickup moves radially outward. Once the disc is positioned via the loading mechanism, a clamp mechanism secures it to the spindle hub, typically using magnetic attraction or spring tension to prevent wobble and maintain centric rotation without slippage. The employs a permanent in the clamp that aligns with the , while spring-loaded designs apply controlled pressure to grip the firmly. Precise speed regulation is facilitated by Hall effect sensors embedded in the motor assembly, which detect the rotor's magnetic position to enable accurate commutation and maintain the required RPM under varying loads. These sensors provide real-time feedback to the servo controller, compensating for any offsets or disturbances to ensure stable CLV operation throughout playback. In high-end CD players, vibration damping is enhanced through rubber mounts isolating the spindle assembly from the chassis and precisely balanced rotors that minimize mechanical jitter, thereby improving tracking accuracy and reducing read errors.

Pickup and tracking assembly

The pickup and tracking assembly in a CD player consists of the movable components responsible for precisely positioning the laser beam over the disc's data tracks to read the encoded information. This assembly integrates optical and mechanical elements to ensure accurate focus and radial alignment, compensating for disc rotation and surface imperfections through closed-loop servo systems. The core of the assembly is the optical pickup unit (OPU), which houses the laser diode emitting at 780 nm, the objective lens for beam focusing, and a array for detecting reflected light. These components are integrated into a compact unit that also includes sensors and actuators for real-time adjustments, mounted on a that slides along a rail for radial movement across the disc. The OPU's positioning is driven by a combination of stepper motors for coarse radial travel in some designs and voice coil motors for finer control, enabling the spot to follow the spiral data track with sub-micrometer precision. The tracking servo handles radial adjustments to keep the aligned with the disc's spiral tracks, which have a pitch of 1.6 μm between adjacent grooves. It employs patterns generated by a that splits the into three beams: a main beam for data reading and two satellite beams offset by quarter-track pitch to detect radial errors via methods like differential push-pull (DPP), where imbalances in reflected light from split detectors produce an error signal proportional to misalignment. This servo uses a to make fine corrections, maintaining tracking within tolerances of 32–48 nm despite disc wobble or vibrations. Complementing this, the focus servo controls vertical lens movement to keep the spot sharply converged on the disc's reflective layer, which lies 1.2 mm beneath the protective cover. An electromagnetic , consisting of coils in a , adjusts the objective lens position to maintain this focus, responding to error signals from astigmatic or Foucault methods that analyze the shape of the reflected beam on quadrant photodetectors. The system ensures in focus error detection over a range of about 10 μm, compensating for vertical disc tilts or movements up to 1 mm. For broader navigation, the sled mechanism provides coarse positioning by moving the entire OPU along the radial rail using a rotary motor coupled to a worm gear or a linear actuator. This enables track seeking over longer distances, with typical velocities reaching 0.064 m/s and accelerations of 4.74 m/s², allowing the assembly to jump thousands of tracks during operations like fast-forward. Short seeks (hundreds of tracks) are handled by the tracking actuator alone, while the sled takes over for extended jumps to minimize wear on fine mechanisms.

Operation and features

Signal processing and output

The signal processing in a CD player begins after the digital audio data, encoded at 16-bit resolution and 44.1 kHz sampling rate, has been extracted and decoded from the disc. This data is fed into a digital-to-analog converter (DAC), which reconstructs the original analog waveform. Early CD players employed multibit DACs, such as resistor-ladder (R-2R) architectures, capable of directly handling the 16-bit precision without oversampling. However, multibit designs proved complex and costly to manufacture with high linearity, leading to the widespread adoption of delta-sigma (ΔΣ) modulators in later models. Delta-sigma DACs use oversampling and noise shaping to achieve effective resolutions beyond 16 bits, pushing quantization noise to higher frequencies outside the audible range. Modern CD players often incorporate hybrid multibit delta-sigma DACs, like the Crystal CS4398 chip, which combine the precision of multibit conversion with the efficiency of delta-sigma modulation for improved dynamic range and low distortion. To enhance performance beyond the native specification, contemporary DACs in CD players support , interpolating the 16-bit/44.1 kHz signal to higher resolutions such as 24-bit depth and 192 kHz sampling rate. This process, performed digitally before conversion, reduces the demands on the subsequent analog by relaxing its transition band and minimizing imaging artifacts. For example, players like the Meridian G08.2 use a dedicated DSP to upsample to 24-bit/192 kHz, employing dual differential delta-sigma converters for channels. Similarly, the Gato Audio CDD-1 features asynchronous upsampling to 24-bit/192 kHz, ensuring low-jitter during the process. These upgrades do not alter the source data but optimize the conversion for smoother analog output, with many units supporting rates up to 192 kHz via integrated chips like the AK4490. Following DAC conversion, the stepped analog signal requires smoothing through an analog , known as the , to eliminate high-frequency components. This filter attenuates quantization noise and spectral images generated by the sampling process, particularly those above 20 kHz, the upper limit of human hearing, thereby producing a continuous faithful to the original audio. In delta-sigma DACs, noise shaping shifts much of the quantization error to ultrasonic frequencies (e.g., beyond 100 kHz), allowing the to focus on removing these artifacts with a gentler compared to early brick-wall designs. Typical implementations use multi-order active filters, often second- or third-order Butterworth types, with a around 20-22 kHz to balance phase linearity and attenuation, ensuring minimal audible distortion while suppressing images up to the Nyquist frequency multiples. The filtered analog signal then passes through output stages designed to interface with external amplifiers or receivers at standard line levels. Unbalanced RCA connectors deliver a nominal 2 Vrms output, providing sufficient drive for consumer audio systems without overload. For professional or high-end setups, balanced XLR outputs are common, often at 2 Vrms per phase (4 Vrms differential) to maintain over longer cable runs and reject via common-mode rejection. These stages incorporate buffer amplifiers, typically op-amp based, to isolate the DAC and filter from load variations, ensuring low (around 50-100 Ω) and stable voltage delivery. Throughout the signal chain, jitter—timing errors in the clock signal—can degrade audio quality by smearing the soundstage and introducing phase noise. Phase-locked loop (PLL) circuits address this by synchronizing the player's internal clock to the incoming digital data stream, regenerating a clean reference with reduced phase variation. In CD players, a PLL acts as a flywheel, filtering out low-frequency jitter from the disc servo while attenuating high-frequency components above its bandwidth (typically 10-100 Hz), thereby minimizing inter-sample timing errors that affect stereo imaging and transient accuracy. Advanced implementations, such as those in the Bel Canto DAC2, employ wideband PLLs with FIFO buffers to further suppress interface jitter, achieving picosecond-level stability for preserved soundstage depth.

User interface and controls

CD players feature a with dedicated buttons for core playback functions, including play to initiate audio reproduction, stop to halt playback, skip forward and backward to navigate between tracks, and eject to release the disc from the loading mechanism. These buttons interface directly with the player's , which translates user inputs into precise servo commands to control the spindle motor, pickup, and other mechanical components for reliable operation. Wireless interaction is commonly provided through infrared remote controls, employing protocols such as for transmitting commands over short distances without line-of-sight obstruction in some RF variants. Remotes typically include a for direct track selection, enabling users to jump to specific songs by entering numbers, alongside buttons mirroring functions like play, stop, and skip. User feedback is delivered via an integrated display, often utilizing (LCD) or (VFD) technology to present essential information such as the current track number, elapsed or remaining time in MM:SS format, index markers within tracks, and total disc playtime. These displays draw from subcode data embedded in the disc to ensure accurate real-time updates during playback. At the core of user interaction management is the CD player's , which processes button inputs and interprets Q-channel subcode data—containing track numbers, timings, and control flags—to enable seamless transitions between tracks, precise pausing that retains position, and resuming from the exact point of interruption. The eject function, when activated, prompts the to signal the loading mechanism for disc expulsion, integrating electronic control with mechanical action.

Audio enhancements and compatibility

CD players often incorporate dynamic range expansion techniques to enhance audio fidelity beyond the standard 16-bit resolution of Red Book CDs. (HDCD) encoding allows compatible players to decode 20 bits of effective resolution from specially mastered CDs by using custom dithering and audio filters that embed additional data within the 16-bit signal. This process restores low-level details and expands the by up to 24 dB compared to standard 16-bit playback, equivalent to four additional bits of resolution. Similarly, players supporting [Super Audio CD](/page/Super Audio CD) (SACD) hybrid discs can access the high-resolution DSD layer for playback, achieving an effective comparable to 20-bit PCM through the 1-bit, 2.8224 MHz sampling rate, while maintaining with the embedded standard CD layer. Many CD players feature digital outputs to connect to external digital-to-analog converters (DACs), bypassing the internal DAC for potentially superior sound quality. The protocol is commonly implemented via coaxial RCA connectors or optical interfaces, transmitting uncompressed PCM audio from CDs at the native 16-bit/44.1 kHz rate. These outputs support sample rates up to 48 kHz as per the IEC 60958-3 standard, allowing flexibility for integration with AV receivers or higher-resolution systems without resampling artifacts. To broaden compatibility with modern media, later CD player models from the early onward include built-in decoders for compressed audio formats stored on data CDs (CD-R or CD-RW). These support files with bitrates ranging from 32 kbps to 320 kbps and WMA files typically up to 192 kbps in (VBR) mode, enabling playback of hundreds of tracks on a single disc while preserving reasonable audio quality for casual listening. For instance, systems like the AVN2210P handle VBR from 48 to 320 kbps and WMA up to 192 kbps, though lossless formats are not supported. High-end CD players employ and filters to improve reconstruction of the analog waveform and minimize . at rates such as 8x (352.8 kHz) or up to 64x (2.8224 MHz) interpolates additional samples between the original 44.1 kHz points, allowing gentler analog reconstruction filters with reduced phase shift and imaging artifacts in the audible band. This technique, implemented in models like the CDP-770 with its 8x digital filter, shifts products to higher frequencies beyond human hearing, enhancing overall clarity without altering the source data.

Variants and applications

Home and stationary players

Home and stationary CD players are designed primarily for fixed installation in domestic audio setups, serving as dedicated components within high-fidelity (hi-fi) systems. These units typically feature robust construction to ensure stable playback in a stationary environment, integrating seamlessly with amplifiers, preamplifiers, and speakers through analog RCA outputs or digital interfaces like and optical connections. Unlike all-in-one receivers, component-style CD players emphasize modularity, allowing audiophiles to customize their systems by pairing the player with separate preamps and power amplifiers, often housed in standardized rack-mount chassis for organized shelving in audio cabinets. All-in-one audiophile CD player systems are limited because they often incorporate built-in speakers or shared components in a single enclosure, which can compromise audio separation through increased crosstalk and interference compared to using dedicated external speakers. Audiophiles prioritize musicality, detail, dynamics, and superior build quality, which are better achieved with separate components that minimize noise, distortion, and design compromises inherent in integrated designs. Build quality in these players prioritizes to minimize mechanical interference with the pickup and disc rotation, achieving a low essential for reproduction. High-end models incorporate heavy bases made from materials like die-cast or multi-layered composites, such as a three-layer structure of metal , damping rubber, and TNRC (Technics Natural Rubber Compound), combined with double insulator systems to decouple external and internal vibrations. Power supplies are frequently isolated using dual dedicated —one for digital circuits and another for analog audio sections—along with separate windings for left/right channels and , reducing electrical noise and . For instance, the Technics SL-P1200 employs a floated power on insulators and four large 3,300 μF electrolytic capacitors for audio rectification, contributing to its 14.5 kg weight and solid cabinet design. Multi-disc changers emerged as a key feature in the late to enable uninterrupted playback of extended collections, with designs accommodating 5 to 200 discs in carousel or vertical stack configurations. Carousel systems, introduced by in , rotate a tray to access multiple discs, while Pioneer's magazine-style changers, first marketed in 1985, load discs into a slotted cartridge for quick swapping. By , these changers dominated the market, offering and functions across discs to suit home listening sessions without manual intervention. Tray loading mechanisms, prevalent in single- and multi-disc home units, slide out horizontally for easy disc insertion, often with motorized operation for convenience. Era-specific examples from the highlight innovations in stationary players, such as the Technics SL-P1200, released in , which utilized a brushless direct-drive servo motor for the spindle to ensure precise rotation and high reliability. This model also featured a Class AA sample-and-hold circuit for clean signal transmission and a microprocessor-controlled for accurate pickup positioning, making it a benchmark for hi-fi integration during the early boom. Similarly, Yamaha's CD-X1 from employed the VMA (Vibration Mechanical Absorber) method for enhanced mechanical stability, underscoring the era's focus on combating vibrations inherent to CD playback technology.

Portable and mobile players

Portable CD players, designed for personal use during travel or commutes, emerged as a key evolution in consumer audio technology following the introduction of compact discs. Sony pioneered this category with the series, debuting the D-50 model in 1984 as the world's first portable CD player, which allowed users to enjoy playback untethered from stationary systems. These devices prioritized compactness and mobility, evolving from early bulky designs to sleeker models that fit easily in pockets or bags. A major challenge for early portable players was disc skipping due to movement, addressed through anti-skip buffering systems that used RAM to store 40-45 seconds of audio data, enabling jog-resistant playback during activities like walking or jogging. Sony's (ESP) and later G-Protection technologies exemplified this, combining digital buffering with mechanical innovations for reliable performance. Power was typically supplied by NiMH or lithium-ion batteries, offering 4-10 hours of continuous playback depending on model and usage, with built-in headphone jacks supporting private listening via included stereo earbuds. Form factors varied to enhance portability, including horizontal layouts for stability and vertical clamshell designs that minimized size while protecting the disc mechanism. Shock protection was further bolstered by electronic suspension systems, such as dynamic damping and rubberized mounts, which isolated the pickup from . Larger variants appeared in boombox-style units, providing amplified for group settings without sacrificing mobility. By the , portable CD technology extended to automotive applications with in-dash slot-loading players, powered by the vehicle's 12V system and featuring auxiliary outputs for integration with existing stereos in many models. These units offered seamless mobile playback, bridging personal devices and vehicle entertainment.

Professional and specialized equipment

Professional CD players designed for DJs and live performance environments, such as the Pioneer CDJ series introduced in the early , incorporate advanced controls for precise mixing and cueing. Early models like the CDJ-500, released in , laid the foundation for digital DJing, while subsequent iterations in the late and early 2000s added features like jog wheels for frame-accurate cueing and , mimicking vinyl turntable manipulation. The CDJ-1000, launched in 2001, introduced touch-sensitive jog wheels, integrated BPM counters for real-time tempo analysis, and hot cue points allowing DJs to instantly jump to up to three predefined track positions during mixes. These elements enabled seamless and transitions, becoming industry standards in club and festival settings. Rack-mountable CD players for recording studios and broadcast facilities emphasize integration with digital audio workstations (DAWs) and high-fidelity signal handling. Models like the CD-6010, a 2U rack-mount unit, feature balanced XLR analog outputs for noise-free connections over long cable runs, alongside AES/EBU and digital outputs for precise . It includes ±16% pitch control to adjust playback speed without altering audio quality in tonality hold mode, supporting adjustments in professional editing workflows. Similarly, Denon Professional's DN-300Z offers balanced XLR outputs alongside RCA unbalanced options, facilitating direct integration into studio racks for reliable playback in production environments. While is common in 's broader lineup for sample-accurate DAW alignment, these players prioritize durable slot-loading mechanisms and compatibility for unattended operation. Commercial jukebox systems, such as those from Rock-Ola and NSM, cater to bars and venues with high-capacity storage and user-friendly selection interfaces. The Rock-Ola Bubbler CD Jukebox supports a 100-disc capacity, allowing operators to load up to 1,500 tracks, and includes a wireless remote for volume adjustment and song queuing from a distance. NSM models like the Fire Bird II, introduced in 1993, also feature 100-CD magazines with over 3,000 selectable titles, integrated remote controls for credit insertion and track skipping, and wall-mount options for space-constrained commercial spaces. These units often include bill acceptors and LCD displays for patron interaction, ensuring reliable performance in high-traffic settings like pubs. Specialized variants of professional CD players incorporate features like pitch-lock, also known as master tempo or key lock, which allows tempo adjustments without varying the musical pitch, preserving harmonic integrity during mixes—a capability refined in 2000s DJ models such as the Pioneer CDJ-1000. This function processes audio in real-time to decouple speed from pitch, enabling DJs to align beats across tracks without tonal shifts. Additionally, MIDI control emerged in late 2000s units like the CDJ-2000, permitting with software controllers and external devices via USB MIDI interfaces for expanded performance options in studio and live setups.

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