Read errors and processing errors Lee (mostly read errors by far). Your DIMM memory in your computer commits errors and you don't even know it because it corrects.
The data path processing electronics in your SACD/DVD contains protection logic that corrects for parity errors.
Yes, state machines correct for data errors on the fly using mathematical error correction code techniques or simple parity correction. There is a lot of overhead in the recorded data that assists in the error correction process.