Block Error Rate
BLER (Block Error Rate) is defined as the number of data blocks per second that contain detectable errors, at the input of the C1 decoder. This is the most general measurement of the quality of a disc. The “Red Book” specification (IEC 908) calls for a maximum BLER of 220 per second averaged over ten seconds. Discs with higher BLER are likely to produce uncorrectable errors. Nowadays, the best discs have average BLER below 10. A low BLER shows that the system as a whole is performing well, and the pit geometry is good. A peak of 100 bad data blocks per second is acceptable for CD-ROM, but an average BLER of 50 per second over the entire disc is a good cutoff point to ensure data integrity.
However, BLER only tells you how many errors were generated per second, it doesn’t tell you anything about the severity of those errors. Therefore, it is important to look at all the different types of errors generated. Just because a disc has a low BLER, doesn’t mean the disc is good. For instance, it is quite possible for a disc to have a low BLER, but have many uncorrectable errors due to local defects. The smaller errors that are correctable in the C1 decoder are considered random errors. Larger errors like E22 and E32 are considered burst errors and are generally caused by local defects. As you might imagine, the sequence E11, E21, E31, E12, E22, E32 represents errors of increasing severity.