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Thread: Sometimes the CD turns out all accurate despite some spots/smudges

  1. #1
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    Sometimes the CD turns out all accurate despite some spots/smudges

    If you compared the same CD that was ripped twice, first time when it had some smudges/spots on it, and second time all smudges cleaned and removed, but both turned out fully Accurate on dbpoweramp, would there be no difference at all in sound quality?

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Not if accuraterip has the same CRC, this means the audio is identical.

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Quote Originally Posted by ripcd View Post
    If you compared the same CD that was ripped twice, first time when it had some smudges/spots on it, and second time all smudges cleaned and removed, but both turned out fully Accurate on dbpoweramp, would there be no difference at all in sound quality?
    It is worth cleaning them first as the ripping time may be reduced and occasionally smudges will cause errors.

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Quote Originally Posted by Oggy View Post
    It is worth cleaning them first as the ripping time may be reduced and occasionally smudges will cause errors.
    To be clear, when Oggy mentions that smudges can cause errors, if you got an AccurateRip match on both rips, there are NO errors. CDs are pretty sturdy it turns out. On the other hand, I've seen brand new CDs, appearing perfect, that have ripping errors. But to summarize, if there is an AR match, you have a bitperfect rip of the CD, smudges or not.

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Gary, sorry to stick this here, but the Private Message link says you have too many stored private messages and can't receive new ones...

    John

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Quote Originally Posted by schmidj View Post
    Gary, sorry to stick this here, but the Private Message link says you have too many stored private messages and can't receive new ones...

    John

    cleared now. thanks.

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Quote Originally Posted by garym View Post
    To be clear, when Oggy mentions that smudges can cause errors, if you got an AccurateRip match on both rips, there are NO errors. CDs are pretty sturdy it turns out. On the other hand, I've seen brand new CDs, appearing perfect, that have ripping errors. But to summarize, if there is an AR match, you have a bitperfect rip of the CD, smudges or not.
    I thought AR was only a measure of "what everyone else reported" and not a guarantee of bit-perfect? Happy to have misunderstood this also ... a bit perfect guarantee would be very nice.

  8. #8
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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Hey Maxpower,

    Quote Originally Posted by Maxpower View Post
    I thought AR was only a measure of "what everyone else reported" and not a guarantee of bit-perfect?
    indeed it is not a guarantee. Accuraterip calculates a checksum for the audio data. This checksum is reported to a database and compared with the checksums of other users for that track. The probability that you have two identical checksums for one track having different audio data tends toward zero. So it is not a guarantee (there is no 100% probability in maths), but nearly as good as one, if different people with different setups have produced different audio files with identical checksums for one track.

    Dat Ei

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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Quote Originally Posted by Dat Ei View Post
    Hey Maxpower,



    indeed it is not a guarantee. Accuraterip calculates a checksum for the audio data. This checksum is reported to a database and compared with the checksums of other users for that track. The probability that you have two identical checksums for one track having different audio data tends toward zero. So it is not a guarantee (there is no 100% probability in maths), but nearly as good as one, if different people with different setups have produced different audio files with identical checksums for one track.

    Dat Ei

    Indeed. I haven't tried to calculate the probability, but the the odds of even 2 people having the *exact* same error on physically different CDs, ripped on physically different computers (because just any old error wouldn't produce the same CRC) so that two bad rips are matching is probably 100s of millions to one. And a 3rd or 4th person and it becomes probably trillions to one. Said another way, it is highly unlikely that I'll sprout wings overnight and be able to fly. But there is some super small probability that I will (very small, but of course all probability distributions have tails). The odds of getting AR matches and the rip not being bit perfect is about the same as me sprouting wings.

    Note, that the above is NOT true if you have an AccurateRip match of only 1, *and* you did a previous rip of that CD and submitted it to the AR database. In this case, you are comparing against yourself.

  10. #10
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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Hey Gary,

    Quote Originally Posted by garym View Post
    I haven't tried to calculate the probability, but the the odds of even 2 people having the *exact* same error on physically different CDs, ...
    it's more likely that one person has a read error, but the checksum matches the AR checksum, but even this tends to zero.


    Dat Ei

  11. #11
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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Actually, what is far more likely if you are ripping is that you are getting accuraterip data for the wrong CD. This is particularly true for CDs with one or few tracks, as you may have already noticed.

    The algorythm used to determine what CD is in your drive uses data from the directory on the CD which contains the number of tracks and where each track begins on the CD. The probability that two CDs have the same track data is much much higher than the probability that the checksums match even though the files don't, particularly if there isn't much track data, like in CD singles. Think about it, it is probably true that dozens of CD singles with every possible track length exist out of the very many CD singles that have been issued (and for which there are accuraterip checksums) But if the audio is different, the checksum will be different even though the track length is the same.

    However notice, this weakness gives you false errors, not false OK's. If you get an Accuraterip OK, the probability of your CD track not actually being identical to those ripped before is infinitesimally small, unless, as other have commented, you previously ripped the same physical CD and you are the only person to ever submit accuraterip data about that CD. In that case, a match only says you got the same results from two rips, not that it matches rips of other copies of the CD.

    Another reason a bad (by listening) CD gives a good accuraterip result is if the pressing plant (or mastering house) messed up and sold a batch of identically bad CDs. As they say, garbage in, garbage out. Your bad CD is identical to someone else's bad CD. I've actually run into this a couple of times over the years. And that doesn't count the cases where the printed label on the CD didn't match the contents! Most recently I got a 2 CD album. The two CDs were properly labeled Disc 1 and Disc 2, but both CDs were actually disc 2! Oops...

  12. #12
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    Re: Sometimes the CD turns out all accurate despite some spots/smudges

    Just wanted acknowledge all the awesome responses here and the depth of knowledge and experience the forum members possess.

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