CD player

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.

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.

[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.

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.

Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels.

[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.

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.

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 sixteen titles).

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.

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.

[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.

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.

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.

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.

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.

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.

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.

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 a SRAM 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 DAC to be converted to an analog audio signal.

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.

Some early optical computer drives are equipped with an audio connector and buttons for standalone CD playback functionality.

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.

This mechanism employs a single laser beam and a set of four photodiodes to read, focus and keep track of the data coming from the disc.

The 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.

[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.

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.