Hardware Reference
In-Depth Information
Manufacturers of CD-DA media were looking for a standard method to combine both music and data
on a single CD. The intention was for a user to be able to play only the audio tracks in a standard
audio CD player while remaining unaware of the data track. However, a user with a PC or dedicated
combination audio/data player could access both the audio and the data tracks on the same disc.
The fundamental problem with nonstandard mixed-mode CDs is that if or when an audio player tries
to play the data track, the result is static that could conceivably damage speakers and possibly hearing
if the volume level has been turned up. Various manufacturers originally addressed this problem in
different ways, resulting in a number of confusing methods for creating these types of discs, some of
which still allowed the data tracks to be accidentally “played” on an audio player. In 1995, Philips
and Sony developed the CD EXTRA specification, as defined in the Blue Book standard. CDs
conforming to this specification usually are referred to as CD EXTRA (formerly called CD Plus or
CD Enhanced Music) discs and use the multisession technology defined in the CD-ROM XA standard
to separate the audio and data tracks. These are a form of stamped multisession disc. The audio
portion of the disc can consist of up to 98 standard Red Book audio tracks, whereas the data track
typically is composed of XA Mode 2 sectors and can contain video, song lyrics, still images, or other
multimedia content. Such discs can be identified by the CD EXTRA logo, which is the standard CD-
DA logo with a plus sign to the right. Often the logo or markings on the disc package are overlooked
or somewhat obscure, and you might not know that an audio CD contains this extra data until you play
it in a computer-based optical drive.
A CD EXTRA disc normally contains two sessions. Because audio CD players are only single-
session capable, they play only the audio session and ignore the additional session containing the
data. An optical drive in a PC, however, can see both sessions on the disc and access both the audio
and data tracks.
Scarlet Book (SA-CD)
The Scarlet Book defines the official standard for Super Audio CD (SA-CD, also referred to as
SACD) media and drives. It was codeveloped by Philips Electronics and Sony in 1999. Unlike the
original Red Book CD-Audio standard, which samples music at 44.1KHz, Scarlet Book uses Direct
Stream Digital encoding with a sampling rate of 2.822MHz—64 times the sampling frequency of Red
Book.
Because of the higher sampling rate and the larger disc capacity necessary to store the audio (as well
as SA-CD's support for video and text content), you cannot play standard or dual-layer SA-CD media
in a standard CD player or computer's CD or DVD drive. Although standard SA-CD media has a
capacity of 4.7GiB (the same as that of single-layer DVD), the formats are not interchangeable. SA-
CD contents are copy-protected by a physical watermark known as Pit Signal Processing, which
cannot be detected by standard computer DVD drives, although some high-end BD and DVD set-top
boxes can also play SA-CD media.
Almost all SA-CD albums use a hybrid dual-layer design, in which the top layer stores standard CD
audio playable on standard CD players and drives, and the lower layer contains the higher-density
SA-CD content. Essentially, a hybrid SA-CD disc is like a CD-audio disc and a standard SA-CD
disc in a single-sided disc (see
Figure 11.16
).
