• What are C2 errors?
  CD-ROMs have different levels of error recognition and correction. One level of error correction is the "C2 error correction". C2 errors can usually correctable , i.e. the CD-ROM itself is capable of fixing a certain number of C2 errors. If to many C2 errors occur, the CD-ROM will interpolate the missing data (i.e. it "guesses" the bad data). Usually correctable C2 errors are not reported (because the errors should usually have been fixed). If to many C2 errors occur (i.e. the errors are not further correctable), most CD-ROMs report a read error. (Some CD-ROMs interpolate silently and only if bigger parts are not readable they will report a read error). There are CD-ROMs that can return additional information where C2 errors occurred and if they were corrected by the CD-ROM.
  
  
• What does C2 errors mean?
  As described above C2 errors normally are correctable error - they are no "real" errors then rather "warnings". On one hand C2 errors are warnings, that there is something wrong with the inserted CD, i. e. the CD is probably dirty or scratched. In most cases it helps cleaning the CD and the C2 errors will disappear. If the C2 errors do NOT disappear this usually means that the CD is slowly "ceasing" - it is strongly recommended to backup the CD!
  On the other hand some CD-ROMs do NOT report normal error messages even if the data haven't been fixed correctly. In this case C2 errors are warnings for possible incorrect (or rather: no longer matching the original) data. Furthermore the error correction - as every error correction - can only fix errors correctly with a certain probability - so if too many errors do occur the error correction might fix an error incorrectly (although this is very unlikely).
  Summary: C2 errors are a sign for a damaged or dirty CD; depending on the CD-ROM C2 errors can also indicate possible wrong data.
  
  
• Counting C2 errors:
  The C2 error correction works byte-per-byte, that is: 1 C2 error per byte - 4 C2 errors per sample - 2352 C2 errors per sector and a maximum of 176.400 C2 errors per second.
  
  
• C2 errors and Feurio:
  Feurio!® can - if supported by the CD-ROM - read C2 error information from the CD-ROM and analyse it. Feurio! can report a C2 error immediately or display the number of C2 errors after the track/ image is read. Analysing C2 errors can be activated under: "Program" -> "Program Parameters" -> "Device Parameters" -> "Special Parameters" -> "C2 Error Messages".
  
  
• C2 errors with data CDs
  The above statements and texts ONLY apply to audio CDs! Data CDs have an additonal error correction level; a C2 error correction is performed as well, but of course incorrect data will not be interpolated. The C2 error information are used as a evidence for possible errors for the "higher" levels of error correction. The "higher" error correction is much more expensive than the C2 error correction and can correct substantial more errors with higher certainty; from there a data CD has a maximum size of 650 MB instead of 750 MB (for an audio CD) - the remaining 100 MB are error correction information. Therefore analysing C2 error correction for data CDs would be a silly thing, because errors can be detected and fixed much better by the "higher" levels of the error correction. From there reading C2 error information with data tracks is not intended for Feurio!®.
  
  
• Which drives support reading C2 error information?
  Unfortunately only a few drives support reading C2 error information correctly. You can find a list of CD-ROMs on the Feurio! homepage on the page "Supported CD-ROMs" ( HYPERLINK "http://www.feurio.com/English/cd_roms/" 00d0c9ea79f9bace118c8200aa004ba90b02000000170000002700000068007400740070003a002f002f007700770077002e00660065007500720069006f002e0063006f006d002f0045006e0067006c006900730068002f00630064005f0072006f006d0073002f000000e0c9ea79f9bace118c8200aa004ba90b4e00000068007400740070003a002f002f007700770077002e00660065007500720069006f002e0063006f006d002f0045006e0067006c006900730068002f00630064005f0072006f006d0073002f000000http://www.feurio.com/English/cd_roms/); all CD-ROMs that have a "Yes" in the column "C2 error" can read C2 errors. Note: CD-ROMs that have a "No" in this column might support reading C2 errors as well - simply try it. Important: We've already found CD-ROMs that are capable of reading C2 errors, but return faulty audio data when the C2 error correction is activated - of course this is not the object of the exercise. Obviously some CD-ROMs still have bugs in the firmware. If the C2 error correction is used with an unknown CD-ROM, the reading quality should be checked once more (device test).
  Who wants to be sure should read the track without C2 error correction first and with activated C2 error correction afterwards and then compare the two tracks with each other. Unfortunately some CD-ROMs do not support reading C2 errors according to the appropiate standards. We got the following answer from a manufacturer to our question about reading C2 errors: "You can return all errors. But the codes are top secret and I would have to kill you if I tell you." So if you should attach great importance to "perfect audio reading" with C2 errors, you have to chose a CD-ROM that is marked as "C2 error capable" in the list at the moment.
  
  
• Automatic recovery/ Reducing the read speed after C2 errors?
  For additional information see: "Automatic recovery/ reducing the read speed after C2 errors?"

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