Tonearm wrote:Are C2 errors always the result of a scratch or can they be in perfect-condition CDs?
C2 errors can and do occur for a variety of reasons, and you can have C2 errors on a disc with no scratches at all.
Tonearm wrote: Can the PlexTools software do C2 error correction?
C2 error correction is always done by the drive's firmware inside the drive, not in external programs. There isn't enough information returned from the drive to allow C2 error correction to be done externally. The best any external program could do would be to note where uncorrectable C2 errors occurred, if the drive supplies such information (not all do), and attempt to re-read those sections of the CD in the hopes of getting an error-free read.
This is essentially what EAC does. It reads multiple times to get the correct data. If the drive doesn't support C2 error reporting, then EAC can't know which areas of the disc are problematic and need to be re-read specifically, and thus it has to re-read the entire disc. This is a slower and less confident process. It is slower because the same data needs to be read again and again. It is less confident because there is no additional, explicit indication of an error that needs to be corrected.
An external program could also attempt to identify the exact samples that went bad and guess at what the correct values should be by averaging adjacent good samples. Some drives do this internally as well. It is known as masking or interpolation. Naturally, this isn't the optimum solution since it is only an imperfect attempt to reduce the effects of the errors, not to correct them altogether.
In summary, it is better to get a drive that does a good job of DAE in the first place rather than to rely on making up for shortcomings later via external software.