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digital Errors And cd Quality

By Bob Speer

Write Errors
Write errors can result in CD failure.  CD manufacturers will reject a master disc if write errors exceed their specifications.
There are three common errors types that affect CD quality.  They are C1, C2, and CU.

C1 Errors
C1 Errors refer to the block error rate (BLER), which consists of bit errors at the lowest level.  C1 errors are always expressed
in errors per second.  All CDs and CDRs contain C1 errors.  They are a normal result of the write process.  However, the
maximum C1 error rate for a quality recording is an average of 220 errors per second based on 10 second samples.

C2 Errors
C2 Errors refer to bytes in a frame (24 bytes per frame, 98 frames per block) and is an indication of a CD player's attempt to
use error correction to recover lost data.  C2 errors can be serious.  In theory, a CD player should correct them.   C2 errors
are usually an indication of poor media quality, or the failure of a CD burner to produce a quality burn (see conclusion).

CU Errors
CU Errors refer to uncorrectable errors that are present after C2 error correction.  No CU errors are allowed in a recorded disc.
Generally, discs with CU errors cannot be played because they contain data that cannot be recovered.

When errors are the result of physical damage to the disc, CIRC Logic - Cross Interleaved Reed-Solomon Code, is used to
identify and correct random errors, which allows some damaged CDs to play without any distinguishable difference.

Conclusion
CD replicators consider a disc with an average of 220 C1 errors per second, "a good quality disc."  Typically, our masters
average less than 1 C1 error per second with absolutely no C2 or CU errors.  We have our own standard which states that in
addition to no C2 or CU errors, we will not ship any disc that averages more than 2 C1 errors per second.  That's .009% of the
maximum allowed for a good quality disc.  This provides you with an excellent master of the highest quality.  If you're going to
have your CD professionally replicated, there is no substitute for a quality master provided by a professional mastering facility.
While mastering is about EQ, dynamics, song levels, etc., it's also about providing you with a low error master that will be
accepted by CD replicators.  We test each master for errors and provide you with full documentation on it's quality.
 
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