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Topic: Wav files compare OK despite CRC mismatch in EAC (Read 3674 times) previous topic - next topic
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Wav files compare OK despite CRC mismatch in EAC

Hi,
After having installed a new CD-R drive (Plextor PX-54TA), I am finally getting decent results when I rip with EAC.

What I have been doing to verify that my rips are OK, is to rip twice and compare the wav files with EAC's "Compare WAVs" tool. A string of perfect matches for the first few albums, and I began to feel safe.

I then tried to copy a few tracks with "Test & Copy Selected Tracks" command to see what CRC results I would get. They all matched, except for one track, yet the log says "no errors occured". I ripped the track once again using "test & copy", and this time the CRC's matched. What I find strange is that when I compared the two wav files i had extracted, they matched OK.

How can this be? Is it that it was the read CRC of the faulty track that was incorrect, while the test CRC was correct? Or is there some other spooky thing going on...? 

All you other perfectionists out there, do you normally use "Test & Copy", or do you settle for a report saying "no errors occured"?

Von

Wav files compare OK despite CRC mismatch in EAC

Reply #1 –
You mean copy value was 'wrong' (different from first try)?

It's the test value that usually differs (at least here), when I re-rip mismatched tracks.

Wav files compare OK despite CRC mismatch in EAC

Reply #2 –
Sorry, I moved too fast, don't remember which one of them that came up different. I'll pay more attention if it happens again.

Do most people use this feature when they rip? (Do you test & copy, or just copy?)

(Edit: typo.)

Wav files compare OK despite CRC mismatch in EAC

Reply #3 –
the very first time I rip a new CD I do a test and copy, subsequent reads, if any, I just do a copy since it already has a test CRC to compare with.

Wav files compare OK despite CRC mismatch in EAC

Reply #4 –
I think that is what I will start to do as well, Shorty.

On a side note, just to be sure: is it possible that two wav files can compare OK in EAC, but still have different CRC values? (Meaning that either the comparison tool or the CRC calculation is not 100% reliable?) I suppose not, but nothing would surprise me anymore... 

Wav files compare OK despite CRC mismatch in EAC

Reply #5 –
Quote
On a side note, just to be sure: is it possible that two wav files can compare OK in EAC, but still have different CRC values? (Meaning that either the comparison tool or the CRC calculation is not 100% reliable?) I suppose not, but nothing would surprise me anymore... 

No because CRC calculation is deterministic - so you'll never get false "crc mismatch" alerts.

On the other hand:
- if several bits (2 or more) are different between the two wav's, there's about 1/4.000.000.000 probability that CRC's still match.
- if only 1 bit is different between wav's, the CRC's will always differ.

If you see "no errors occured" after a crc mismatch, it's an EAC bug. Btw I can't understand how it's still not fixed.

Wav files compare OK despite CRC mismatch in EAC

Reply #6 –
I always test and copy. At 25x, I can afford it.

Wav files compare OK despite CRC mismatch in EAC

Reply #7 –
Quote
If you see "no errors occured" after a crc mismatch, it's an EAC bug. Btw I can't understand how it's still not fixed.

I doubt it is a bug, actually.

EAC is very good but not perfect. A CRC mismatch indicates that EAC made two extractions with different results.
I don't think we are talking about a bug: EAC's secure mode is designed to work without test & copy. That might be why "it's still not fixed".
Of course it would be (as you seem to suggest) more practical if EAC gave a kind of warning in a case like this one.