About CD

CD player is actually what we commonly refer to in daily life as a CD player, and some people also call it a laser disc player or a laser turntable. It is an intelligent high-fidelity stereo audio device controlled by a microcomputer, utilizing advanced laser technology, digital technology, computer technology, and various new components. It has the advantages of high-density recording, long playback time (up to 60–75 minutes), easy operation, and fast track selection. It can realistically reproduce recorded content, with clear layering and a sense of presence. Its audio performance specifications are very high, featuring a wide dynamic range, frequency response from 5 to 20,000 Hz, and distortion as low as 0.003%. Today, CD players have become very common audio playback devices, and they can be classified into two types based on their appearance: desktop and portable.

Principle of construction
　　CD phono is mainly composed of laser pickup and turntable system, servo system, signal processing system, information storage system and control system. The laser pickup is a key component of a CD record player, consisting of a semiconductor laser, an optical system, and an electrical detector. The laser is a low-power (MW-level) AIGAS laser diode, the laser beam emitted is projected onto the information surface of the record through the optical lens system, because many pits are recorded on the record, so when the light point hits the pit, the signal picked up by the photodetector is small because the reflected light is weak; When the light spot hits the aluminum film without pits, the reflected light is strong, and the signal picked up by the photoelectric detection is large, so that the corresponding presence or absence of the pit will generate a corresponding high and low level electrical pulse signal at the output of the detector, and then pass through the RF amplifier, and obtain the serial digital signal of “1” and “0” by its internal comparator, and add it to the digital signal and processing circuit for demodulation, frame synchronization signal detection, error correction processing, etc., and add the processed data to the digital-to-analog converter (D/A), and then the converter will be output as an analog sound horn.
　　The bright CD discs are made of extremely thin aluminum or gold sound film with a protective layer of PVC plastic. Like floppy disks and hard disks, CD disks can store information in the form of binary data (data patterns consisting of “0s” and “1s”). To store data on a disc, the data must first be converted into binary with the help of a computer, and then the data pattern must be burned with a laser on a flat, reflective platter, with the small pit carved by the laser representing “1” and the blank space representing “0”. When reading data from a CD disc, a directional beam (laser) moves rapidly across the surface of the disc. A computer or laser record that reads data from a disc looks at every point the laser passes through to determine if it reflects the laser light. If it doesn’t reflect the laser (there’s a small pit there), then the computer knows that it represents a “1”. If the laser is reflected back, the computer knows that the dot is a “0”. Then, these thousands, or even millions, of “l” and “0” are restored to music by computers or laser record players！