User Manual

Subcode channels R through W (remaining six bits)
Some CD players ignore the R-W channels, while others use them to display additional information, such as the title of the CD, name of
the artist, and track titles, if the information is available on the CD.
A common term used when recording audio to a compact disc is “PQ editing”. PQ editing allows you to edit the P and Q channels on the
disc. This allows you to increase the length of pause time between tracks and during Lead-In. Pause is the area on a disc that precedes
audio tracks (between index 0 and index 1). The Red Book standard calls for a minimum of two seconds of pause time between tracks on
all audio CDs, but with track editing, this can be virtually any length you desire.
Lead-out area
The lead-out area contains 90 seconds of silence (blank sectors) and indicates to the player that the end of the data has been reached.
The lead-out area is the portion of the disc most likely to be damaged as a result of handling. As you know, discs are most commonly
handled by the edges. If audio was stored in these areas, it would likely become difficult for your CD player to read.
CD error detection and corrections
The error detection code and error correction code (EDC/ECC) found in each frame of the compact disc is essential to the success of the
compact disc. Without it, any digital recording on tape or disc that has become damaged would sound just like a badly scratched LP. In
fact, without error correction, the feasibility of digital audio would be destroyed.
Fortunately, when you scratch a CD, the nature of the data on the disc and the design of the CD player prevent any errors. By encoding
all data recorded to the compact disc with a special error correction code, the CD player can use the code to correct damaged data and
deliver the original audio. An example of how error correction works is as follows. Assume that the first line below represents
information on an LP groove and that the second line represents information on a CD pit track:
With temperatures of -40ºF, Madison is the perfect vacation spot.
CD-Architect is here! CD-Architect is here!
Now place one of your fingers vertically over these two lines. This represents a scratch. As you can see, a portion of the message on the
LP is gone forever, whereas the information on the CD can still be understood. By utilizing and comparing redundant data, the CD is able
to read the message and overcome the effect of the damage. This error correction does have a cost though: messages using error
correction require more storage space.
Before this error correction can take place, errors must first be detected. This is accomplished through the use of parity bits. A parity bit
is a bit added to every data word, which makes the total number of 0s or 1s in the word even or odd. For example, a parity bit rule may
state that all data words with an odd number of 1s are invalid and all data words with an even number of 1s are valid. The CD player
would then eliminate all odd-numbered data words and keep all the others. Unfortunately, if a large error occurs and wipes out all of the
parity bits and data, this method becomes useless. As a result, a multiple number of parity bits are used to detect errors. To provide
additional help in dealing with large groups of errors, called burst errors, an error protection scheme called interleaving is used in
conjunction with parity bits.
Interleaving is used to guard against burst errors and can be thought of as shuffling a deck of cards. Data is shuffled in the bit stream
prior to recording so that consecutive words are never next to each other on the disc. When interleaved data is finally de-interleaved,
consecutive errors are scattered throughout the disc and errors can be more easily corrected.
Interleaving is taken one step further by interleaving data numerous times over long and short time intervals. This process is called cross
interleaving, and utilizes Cross Interleave Reed-Solomon Code (CIRC) to execute both parity checking, which checks for random errors,
and cross interleaving, which permits parity bits to correct burst errors on the disc. By utilizing CIRC in the first two layers of error
protection on each frame of the disc, the majority of all CD damage can be effectively repaired and replayed without any distinguishable
difference.
It is important to remember that error correction does have its limitations. Depending on the severity and nature of the error, the
damage may be so bad that no amount of ECC, EDC or TLC will bring back the music. In this case, you will hear a skip on the CD.
10 | CHAPTER 1