Handbook for Sound Engineers

Optical Disc Formats for Audio Reproduction and Recording 1141

computed using coefficients derived from a low-pass
filter response. In this way, when these samples are
summed with other such samples, the output data stream
corresponds to the sin (x)/(x) impulse response
processing of an ideal low-pass filter. Following this
processing, the data is converted into a format appro-
priate for the type of D/A converter used in the player. In
most CD players, sigma-delta D/A converters are used,
employing techniques such as short word lengths, very
high oversampling rates and noise shaping.
Also present in the audio output stage of every
player is an audio deemphasis circuit. Some CDs are
encoded with audio preemphasis characteristic. On
playback, this is detected and deemphasis is automati-
cally carried out, resulting in an improvement in
signal-to-noise ratio.

30.4 Other CD Formats

The CD’s small size, economy, robustness, and capac-

ity make it an excellent music carrier. However, its util-

ity is not limited to music playback. Other formats,

including computer-based storage and recordable for-

mats, have been derived from the original Red Book

standard. In particular, the CD-ROM, CD-R, and

CD-RW formats are widely used in computer applica-

tions as well as stand alone audio applications.

30.4.1 CD-ROM

The CD read-only memory (CD-ROM) standard,

sometimes called the Yellow Book standard, is codified

as the ISO/IEC 10149 standard. It is derived from the

CD audio standard but defines a format for general data

storage and is not tied to any specific application.

Ninety-eight CD frames are summed to form a data

block of 2352 bytes (24 bytes × 98 frames). Each disc

holds 330,000 blocks. The first 12 bytes of a block form

a synchronization pattern, and the next 4 bytes form a

header field for time and address flags. The header

contains three address bytes, represented as disc times,

storing minutes, seconds, and block numbers within the

second. The header also contains a mode byte;

depending on the mode selected, the remaining 2336

bytes can store user data, or 2048 bytes of user data

with extended error correction.

The mode byte identifies three modes and is used for

two different data types, shown in Fig. 30-10. Mode 1

permits 2048 bytes of user data in each block. Each

block contains 2 Kbytes (2 × 1024) of user data;

280 bytes are given to extended error detection and

correction (EDC/ECC). A Mode 1 CD-ROM holds 682

million bytes of user information (333,000 blocks ×

2048 bytes). Mode 2 gives the full 2336 bytes to user

data. A CD-ROM bit stream is applied to conventional

CD encoding so that CIRC, EFM, and other processing

is applied. Mode 1 thus has two independent layers of

error correction (EDC/ECC and CIRC) whereas Mode 2

uses only CIRC error correction.

Because of its extended error correction, EDC/ECC

data independently supplements the CIRC error correc-

tion code applied to the frame structure, improving the

error rate over that of audio CD. Mode 1 is employed

for numerical data storage, which is more critical than

audio data. In EDC/ECC encoding, a GF(2^8 )

Reed-Solomon product code (RS-PC) codes each block.

It produces P and Q parity bytes with (26,24) and

(45,43) code words respectively.

The CD-ROM/XA format is an extension to the

Mode 2 standard and defines an XA data track that can

contain diverse data such as computer, and compressed

audio and video. However, CD-ROM/XA differs from

CD-ROM Mode 2; XA provides a subheader that

Figure 30-10. CD-ROM Mode 1 contains 2048 bytes of user data with extended

error correction, and Mode 2 contains 2336 bytes of user data.

Block address 3

Min

1

Sec

1

Block

1

Mode 1

1

User data

2048 EDC

4

Space

8

P

Parity

172

Q

Parity

104

Sync

12

Header 4

ECC 276

Block address 3

Min

1

Sec

1

Block

1

Mode 2

1

Sync

12

Header 4

Mode 1

Mode 2

User data

2336