CIRC's Role in CD Mastering
Your first question, more than likely, will be what exactly is CIRC or Cross-Interleaved Reed-Solomon Code? I could easily write about the technical side of CIRC but then this article would easily be several pages long. I will to try to explain the CIRC concept in laymen terms.
CIRC deals specifically with the issue of error detection and correction. All CD’s are incorporated with CIRC. CIRC is a powerful error detection code that can detect and completely correct all errors on a reasonably good disc.
The first step any good and professional CD mastering company will take once they receive a pre-mastered CD, will be for the CD mastering engineer to run the CD through a high end program that will evaluate the quality of the CD. If a major error occurs and a sample cannot be perfectly reconstructed by the error control circuitry, it may be possible to "guess" the content of the sample; that is, obtain an approximation by interpolating it off the neighboring audio samples. While this concealment will not "fix" the error, it will make it inaudible, offering a graceful degradation of audio quality as clicks and pops are avoided.
This same program will tell them the compatibility between the writer and the media and which type of media works best. In return this allows the mastering engineer to optimize disc quality and avoid problems, especially since media quality varies with each batch. Then the CD mastering engineer can discover bad batches to save them time and save customers money
Keep in mind that all CD's are not made equal and quality will vary, sometimes dramatically. Any errors that occur usually are a result of poor disc quality, type of burner used, or what speed the pre-master was burned at.
In GENERAL terms, the higher the speed you burn at, the more errors you will get. Even the opposite is sometimes true as well. If you burn slower that 4X you create an emulsion of the recording and makes the recording prone to different types of errors.