Hardware Reference
In-Depth Information
• The ISRC (International Standard Recording Code). This is unique to each track
(song) on the disc.
The R-W subcodes are used on CD+G (graphics) discs to contain graphics and text. This
enables a limited amount of graphics and text to be displayed while the music is being
played. The most common use for CD+G media is karaoke “sing-along” media. These
same subcodes are used on CD TEXT discs to store disc- and track-related information
that is added to standard audio CDs for playback on compatible CD audio players. The
CD TEXT information is stored as ASCII characters in the R-W channels in the lead-in
and program areas of a CD. On a CD TEXT disc, the lead-in area subcodes contain text
information about the entire disc, such as the album, track (song) titles, and artist names.
The program area subcodes, on the other hand, contain text information for the current
track(song),includingtracktitle,composer,performers,andsoon.TheCDTEXTdatais
repeated throughout each track to reduce the delay in retrieving the data.
CD TEXT-compatible players typically have a text display to show this information, ran-
ging from a simple one- or two-line, 20-character display, such as on many newer RBDS
(radio broadcast data system) automobile radio/CD players, to up to 21 lines of 40-color,
alphanumeric or graphics characters on home- or computer-based players. The specific-
ation also allows for future additional data, such as Joint Photographic Experts Group
(JPEG) images. Interactive menus also can be used for the selection of text for display.
Note
Current versions of Windows Media Player (WMP) do not natively support CD TEXT for
playback or during the creation of music CDs. However, a free plug-in called WMPCDText
is available to add CD TEXT support to WMP. Other media players such as Winamp
(
www.winamp.com
)supportCDTEXTnatively.PopularCD-burningprogramswithsupport
for CD TEXT include Nero (
www.nero.com
)
, Roxio Creator (
www.roxio.com
), and the free
ImgBurn program (
www.imgburn.com
).
Handling Read Errors
HandlingerrorswhenreadingadiscwasabigpartoftheoriginalRedBookCDstandard.
CDs use parity and interleaving techniques called
cross-interleave Reed-Solomon code
(CIRC) to minimize the effects of errors on the disk. This works at the frame level. When
being stored, the 24 data bytes in each frame are first run through a Reed-Solomon en-
codertoproducea4-byteparitycodecalled“Q”parity,whichthenisaddedtothe24data
bytes. The resulting 28 bytes are then run though another encoder that uses a different
scheme to produce an additional 4-byte parity value called “P” parity. These are added to
the28bytesfromthepreviousencoding,resultingin32bytes(24oftheoriginaldataplus
the Q and P parity bytes). An additional byte of subcode (tracking) information is then
