In 1979, Philips and Sony formed an alliance to jointly develop the CD-DA (Compact Disc-Digital Audio) standard. Philips has already developed a commercial CD player, while Sony has more than ten years of experience in digital recording technology research. When they agreed to regulate a single audio technology, the two companies got into a quarrel-which introduced a potentially incompatible audio laser disc format.
Philips (Phlipis) mainly conducts physical design. The CD it designs is similar to the previously produced CD discs. The pit and land on the disc can be read by laser; Sony Mainly carry out the design of digital-analog circuit, especially the design of digital coding and error correction code.
In 1980, these two companies issued the CD-DA standard, which is today's Red Book standard (named because the cover of the published document is red). The Red Book includes specifications for recording, acquisition, and the 120mm (4.72 inch) diameter physical format still in use today. It is said that the size of this disc is determined because it can hold the entire content of Beethoven’s Ninth Symphony for about 70 minutes without interruption.
After the specification was released, the two companies competed to launch the first commercial CD audio drive. Sony (Sony) has a wealth of experience in digital circuits, and finally won after a month of competition with Philips (Phlipis), and launched the CDP-101 player and the world's first CD on October 1, 1982. Record-Billy Joe's 52nd Street album. The player was first launched in Japan, then in Europe, and did not enter the US market until early 1983. In 1984, Sony introduced the first removable portable CD player.
The CD turntable is the first member of the CD family, and its standard is the basis of other CD standards. Sound is a continuously changing analog quantity, which is traditionally recorded by analog. CD-DA overcomes the weaknesses of analog turntables and uses digital methods to record sound information. The basic method is as follows:
(1) Sampling and quantization
The analog sound signal is converted into a digital signal through sampling and quantization.
The so-called encoding is to add certain error correction, synchronization and control data to the useful data. During data playback, it can be judged whether the read audio data is wrong according to the recorded error correction data. If there is an error within a certain range, it can be corrected. CD-DA uses CIRC, an error check code, to detect and correct errors caused by scratches or dust on the CD surface.
In CD-DA, stereo has two channels (left and right channels), so each sample has two 16-bit (bit) samples, which form two 8-bit bytes (byte ). A total of 24 bytes in 6 samples form a frame, with 12 bytes for each of the left and right channels. The Red Book defines 98 frames to constitute a section (Section), also known as a sector (Sector).
The sampling frequency of CD-DA audio data is 44.1kHz, so the audio data rate of 1 second is
44.1×1000×2×(16÷8) = 176400 words Section/second
The number of frames required for 1 second is
176400÷24= 7350 frames/second
The number of sectors required for 1 second It is
In other words, each sector is 1/75 second in length and contains 2352 bytes of digital audio data.
In addition to the left and right channel audio data, each frame also includes: 3 bytes of synchronization signal (SYNC), 1 byte of control and display subcode (subcode/control and display), 4 Byte Q error check code, and 4-byte P error check code (table 11-02-1).
One frame of CD-DA
Audio data (left channel)
Audio data (right channel)
4 bytes< /td>
The synchronization bit is no longer modulated by EFM (Eight-fourteen Modulation), it is the channel code itself. The specific codeword is:
Any code that is the same as the synchronization codeword will not appear after any data is modulated by EFM. The subcode mainly provides disk address information. Both Q check code and P check code use RS (Reed-Solomon, Reed-Solomon) code, where P check is a check code generated by (32, 28) RS code, and Q check is made by (28, 24) Check code generated by RS code.
The amount of audio data contained in each sector is 98×24=2352 (bytes):
< b>Audio data contained in one sector
|< td width="44">|
Number of channel bits
Sync bit (SYNC)
Left channel data (Data)
Q check code
|< p>Left channel data (Data)|
P check code
|< p>68 p>|
The Red Book stipulates that the audio data on the CD is stored in one or Multiple tracks (tracks). Each track is usually a song. There can be up to 99 tracks on a standard CD-DA. A track can contain several sectors.
The Red Book not only defines how to store audio on a CD, it also defines a method for adding image information to the CD. This type of disc is usually called CD+G disc, or "CD plus graphics" disc. Approximately 16MB of images (user data) can be stored in the subcode (channels R~W) of a 74-minute Red Book standard CD.
The encoded data is modulated and converted into channel codes to determine the length of the pits and bumps on the disc. The audio data, control and error correction codes are recorded on different tracks when the disc is recorded. This is also called the Red Book or Mode 0 specification. A CD turntable can theoretically hold about 74 minutes of stereo music signal. The success of CD turntables quickly replaced ordinary phonographs and compact discs.
Part of the content of the Red Book is summarized in Table 11-02-3.
All optical disc formats are developed based on the CD-Audio format.
Summary of CD Disc Standards
Clockwise (from the reading surface)
1.2m/s~1.4m/s (constant linear velocity)
Light Track spacing
disk Film diameter
Center Hole diameter
46 mm～117 mm
Data signal area
50 mm～116 mm
Any material with a refractive index of 1.55
Minimum pit length
0.833 μm (1.2m/s)～0.972 μm (1.4m/s)
Maximum pit length
3.05 μm (1.2m/s)～3.56 μm (1.4 m/s)
|< p>780 nm (7 800 Angstroms)|
Depth of focus
± 2 μm
Signal format< /p>
Number of channels
16-bit linear quantizationp>
Channel bit rate
4.3218 Mb/s< /p>
Data bit rate
1.9409 Mb/ s
Data: channel bit
Error correction code
CIRC(Cross Interlea ve Reed-Solomon Code)