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EAC CRCs & ACCURATE RIP CRCs, Still Confused
prbatman
post Jul 20 2004, 15:50
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crying.gif Hello Again.

Still a bit confused over tis CRC business.

Example:

Say I rip a CD via EAC to WAV on one Drive ,then Rip the same CD on another Drive.Apart from WAV COMPARE the way I check they are exact is via the COPY CRCs generated via EAC.

I was under the impression that the COPY CRCs were 'fingerprints 'of the tracks.Therefore they would be the same(As long as Drives are set correctly)On any CDROM/DVDROM.

I am correct in thinking this would be the case if the same CD is ripped with a number of different drives correctly set up using EAC.
(All COPY CRCs would match)

The confusing part...when accurate rip checks you have a perfect copy,and it confirms you have.It gives a completely different set of track CRCs.

Could anyone who knows about it.Please explain why the CRCs are different .I thought if a CRC was a fingerprint it would be the same whether generayed by EC or ACCURATE RIP.

And if I've got the fingerprint theory wrong.What exactly is a CRC/COPY CRC.

Thanks,
Ian
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Otto42
post Jul 20 2004, 17:29
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QUOTE (prbatman @ Jul 20 2004, 09:50 AM)
Still a bit confused over tis CRC business.
*

This really isn't that hard to understand here. The only difference is that AccurateRip uses a different algorithim to calculate the CRC value. So it gets different CRC's. But they're both the same across machines.

In other words, if you rip a CD on two machines, the EAC CRC's should match up, and the AccurateRip CRC's should match up, but they won't match each other.

CRC stands for Cyclic Redundancy Check. CRC is a *type* of method for calculating a checksum type of value. But it is not a specific *algorithim* for doing so. In other words, many, many, many different ways to calculate a CRC exist, and they're not all going to give you the same "CRC" number at the end of it.

EAC uses one method. AccurateRip uses another. They will both consistently provide the same answers given the same data, but they will not give the same answers as each other do.

To oversimplify, basically a CRC is calculated by treating the data you want to check as one big long number, which you then divide by some other number. The remainer from this division is the CRC. What number you actually divide by is up to you. Some common numebrs exist. CRC32, for example, uses 0x04C11DB7 as the divisor. This is implemented in anything that uses CRC32, such as PKZIP, WinZip, PNG, etc. And so given the same data, these all get the same CRC number. But you can really use any number as the divisor, and other methods do just that.

This post has been edited by Otto42: Jul 20 2004, 17:34


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prbatman
post Jul 20 2004, 17:41
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wink.gif Thankyou .It does make it a lot clearer when it's explained like that.
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