It probably means no interpolation i.e. it used the built in error correction codes and redundancy in order to grab a bit-perfect copy of that which was encoded on the disc, this is part of the design of Redbook CDs (and in fact, the physical medium itself) 
If you’re playing the disc on a standard CD player then maybe there’s a difference in error correction. However, if you’re playing the disc on something like a PWT (Perfect Wave Transport) then the exact same bits with the exact same timing will result and there should be no difference in SQ assuming the special copy is not altered/filtered/whatever.
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Yes, it means an accurate copy was made but error correction would have been employed to make that copy. AccurateRip reports on the end result, not how you got there.
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I disagree. In my opinion there is no way error correction could get the identical CRC data that AccurateRip uses to verify a good read.
CD error correction does not involve inserting random bits or guesses. Rather, there are error detection and correction schemes built into the format. This way the data which eventually comes out is bit perfect. Similar error correction schemes are used on hard drives.
It is important to understand every CD inherently contains many, many errors. This was known at the time the Redbook specification was created. Thus, error correction is built into the spec.
As i previously mentioned, one scheme is interleaving redundant copies of the data on the disc. When an error is detected, the transport looks elsewhere for a correct copy. Once it find a correct copy (and the cyclic redundancy check value is correct) this data is substituted for the error. This is true for playback as well as during ripping.
As an analogy, suppose you had a one page poem in storage. You take out a copy, and find that the total of the assigned value of letters in this copy is incorrect (the CRC check failed). You then check the next copy and find it too fails, but the third copy CRC is correct, as is the seventh copy. You now compare the two correct copies and find them identical. You now know you have a correct copy and you photocopy it. AccurateRip takes a look at the photocopy, finds the CRC value matches its database, and signs off on it
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There are many types of error correction. The maths can be complicated but, by definition, error correction means that you can recover the 1 or 0 accurately from the source when the 1 or 0 is unable to be directly read.
The Reed-Solomon algorithm does this and it’s predictable just how many errors can be present before the algorithm fails to error correct.
You and I can have two different copies of a CD with errors in different spots. As long as each of our CDs is below the threshold for which the algorithm can error correct then the resulting rip’d file will be the exact same and therefore the CRC, the checksum for which AccurateRip is verifying against, will come back as an identical copy. It does not mean our physical CDs are identical it just means they are both good enough to extract identical 1s and 0’s from. And, in for a rip’d file, that is all that matters.
However, the CDs could sound different in the same CD transport depending on how much additional read / error correction must be done to extract the data and if that additional processing translates to any kind of reduced SQ resulting because of noise or some other factor not accounted for in the transport design.
But, the rips are still bit-perfect and identical. As @Elk pointed out there are all kinds of error correction happening within digital copies and movement of data. The reason these exist is that it is expected the data will have errors. The algorithms make sure the errors do not cause data corruption. That isn’t a guess… that is a mathematical guarantee that the algorithm can calculate if the error should have been a 1 or a 0. And, when the algorithm fails, then that bit fails and and you do end-up with data corruption. That’s when our rips will be different. Not because of error correction but because the error correction was not able to recover the error.
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Nicely explained. Thanks!
It is a bit difficult initially wrapping one’s head around the reality data storage (and data transmission) is inherently full of errors, this is expected, and there are ways to guarantee its accuracy.
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Thanks for all the knowledge guys.
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