Silver ring CD in Hong Kong: The biggest difference between silver ring CD and ordinary CD is that the inner ring of CD is different. The inner ring of silver ring CD (some CDs together with the disc body) is silver, while the inner ring of ordinary CD is made of transparent plastic, so it is also called "apron version". In addition; 199 1 years ago, most of the albums released by Hong Kong singers were almost the first edition of silver circle CDs, followed by ordinary CDs and reprinted CDs, so they were also called "the first batch of silver circle versions", with a small number of productions and extremely rapid appreciation. Because after 1992, we didn't continue to produce silver ring CDs! Ordinary CD: the sampling frequency of ordinary CD records is 44. 1kHz, 16-bit quantization. It can achieve a frequency response of 20-20kHz, a dynamic range of 90DB and a signal-to-noise ratio of not less than 90DB. The frequency response of ordinary CD is very flat, the noise floor is very small and the dynamic range is quite large. The sound stage depth and width of replay are also narrow and tight, and the overall sense of space and presence is not very good. Improved ordinary CD: 1994, American Tayrac record company has released 20-bit recorded CD records. In the process of recording and editing the master tape, the dynamic range reaches 1 12DB. Then it is converted into 16 bit for digital tabletting. 1995, TELARC Records Company of Tayrac, USA released a CD record of two-channel surround sound recording. This is of stage significance in the history of records. Because through the two-channel surround sound, you can hear the deeper and wider sound stage in the ordinary stereo system, and you can feel a certain degree of encirclement. In fact, as early as 1986, Tayrac Records Company introduced the technology of two-channel surround sound to record and distribute CD records. However, the two-channel surround sound recording technology at that time was still in the experimental stage. HDCD: 1992, which is developed on the basis of ordinary optical discs. HDCD means high-precision CD records. In the same year, RR Records released the HDCD sample numbered RR-S3CD. The main technical principle of HDCD is: recording with 18 bits. During the recording process, 16 bits are common full-band digital recording; The other two bits are specially used to record high frequency and ultra-high frequency containing a lot of phase information through high-pass filters and other devices. Then, when editing the master, the full-band part is compressed into 14 bits, and the phase-specific 2 bits are recorded separately. Then it was written into HDCD records. When HDCD records are played on ordinary CD players, only 14 full-band audio signals can be read. At this time, the dynamic range can only reach 78DB. HDCD records and players really became popular in 2000. During this period, CD records in various formats were published, and CD records and DVD audio formats were officially launched. DDDD: 1993, DG Records of Germany introduced the 4D recording format. At first, CD records only had three D's, namely, digital recording, digital mastering and digital compression (DDD). Among them, there are three other ways: this is AAD mode of analog recording, analog master and digital tabletting; Add analog recording, digital mastering and digital tabletting modes, and DAD mode of digital recording, analog editing and mastering and digital tabletting. 4D recording is a digital mixer with analog and digital converters and microphones at the front end of the digital recorder. At the same time, 2 1 bit quantization is adopted. The original dynamic recording range reached 1 18DB. The fineness and sweetness of the sound have been greatly improved. Then the master is edited and made in the way of 2 1 bit, and finally converted into 16 bit for digital tabletting. SACD: SACD is a second-generation high-density optical disc jointly developed by Philips and Sony. The sampling frequency of SACD is 2.8224MHz, which is 64 times that of ordinary CD. SACD adopts DSD(Direct Stream Digital) digital audio technology, which is 1Bit from beginning to end without any conversion. There are two forms of SACD, one is pure SACD. It is not compatible with any type of playback device except the dedicated playback device. SACD also has a method of manufacturing composite optical discs. The lower layer of the record is SACD, and the upper layer is ordinary CD. It belongs to a typical single-sided double-layer structure.