4 Replies Latest reply: Jun 12, 2010 10:48 AM by ed2345
mwheelerk Level 1 Level 1 (5 points)
When importing CDs into iTunes there is an option for Use Error Correction. There is a minimal explanation under Help as to what it does but not as to how. Does anyone know how the Error Correction process works. Is there a check against a data base comparing the rip against others to verify accuracy? Any details you can provide is appreciated.

My interest in knowing is maintaining the highest quality and most accurate iTunes library possible.

iMac 20 inch late 2007 1GB RAM 250 GB HD, Mac OS X (10.6.3), Time Capsule, Apple TV, My Book External Hard Drive
  • Jolly Giant Level 7 Level 7 (25,440 points)
    found in another discussion on another forum:

    David Charlap
    Don Hurter asks what "Use error correction when reading Audio CDs" does.
    Audio CDs have error correction codes on the disc, so that errors (like manufacturing defects, scratches, fingerprints, and even some copy protection schemes) can often be played through without corrupting the sound.
    When you rip a CD, the computer reads the raw audio data from the disc. Typically, it just reads the audio samples and ignores the error-correction codes, assuming that the data will be good. This means that if there are any errors on the disc, those errors will become defects in the sound (typically heard as pops or clicks.)
    When you turn on the "use error correction" feature, iTunes will process the error correcting codes along with the audio samples, using them to correct any errors it finds. If your computer is fast enough (relative to the drive's audio-extraction speed), you won't notice a slowdown (but you may notice an increase in CPU usage.) If the computer is not that fast, using error correction will slow down the ripping.


  • mwheelerk Level 1 Level 1 (5 points)
    What I would like to know is what are those audio samples they are comparing and where are they coming from. If they are within the CD itself I am unsure of the value. If they are pulling a comparison sample against some other database that would be interesting to know. Many people believe that iTunes does not do bit accurate rips. I am satisfied with iTunes but I am interested in knowing the source of the comparisons correction data.
  • Chris CA Level 9 Level 9 (77,005 points)
    what are those audio samples they are comparing and where are they coming from.

    It isn't comparing audio samples on the CD to other audio samples.
    Basically, let's say there are 20 bytes written on the CD. The 21st byte is the sum of the previous 20 bytes.
    If they don't match there is an error. Either the bytes are reread or the application "guesses" what should be there.

    Here's a pretty good explanation -> http://home.btconnect.com/geffers/cd.html
  • ed2345 Level 7 Level 7 (20,590 points)
    mwheelerk wrote:
    Many people believe that iTunes does not do bit accurate rips.

    If you'd like to see more about the mathematics of error detection and error correction, see here => http://en.wikipedia.org/wiki/Errorcorrectingcodes

    True or not, your statement (about iTunes not doing bit accurate rips) is a common belief. There are other ripping tools, such as Exact Audio Copy, that claim to have much more powerful error correction.