I had a question about EAC C2 vs. Non C2,

I have a CD I extract with EAC, C2, T&C, get matching CRC's then try non C2, T&C & get different (than C2 enabled) matching CRC's then extract with another drive non C2 & find CRC's to match & be the same as non C2 on the first drive.

Does this mean C2 failed? or is it possible that EAC's non C2 error detection/correction methods failed?

1) Use WAV compare, see what it shows.

2) Wipe off the CD with a CD wipe and try it again.

3) See which one skips more. Keep the one that skips less.

It depends on the drive. If they are different, than see which is better, and that'll be the mode to go with. B)

My question was in theory & was asking a specific question, not which copy should I keep or whether to use C2 error info

Since two different drives give you the same CRC with C2 disabled, isn't it most likely that the first drive w/ C2 enabled is the problem rip? Then that would imply that the problem was in the C2 detection of the first drive.

My understanding is that without the "Drive is capable of retrieving C2 error information" box checked, EAC will read all data twice, but with that box checked, it will only reread locations where the drive identified a C2 problem. (If I'm wrong, somebody please correct me).

It would be helpful to know what happens with a rip using the second drive and C2 enabled. If it agrees with the two rips using C2 disabled, then the problem is definitely with C2 detection on the first drive. If you get a CRC different from all three of the previous rips, then probably both drives have a C2 detection problem. If the two drives with C2 enabled give identical CRC's, different from the rips with C2 disabled, that would call for some real head-scratching.

The drive must not be accurate stream, and have a variable offset, thus giving you different reliable CRCs from time to time. Get Feurio and let it test your drive.

Other explanation : the use of C2 introduces an offset. Perform a compare wav process on the file got with C2 (CRC 1) and the one got without C2 (CRC 2) to see if there are different samples (read error), or missing/repeated samples (offset).
It has been said long ago by an expert whose name I don't remember, that the offset should be different reading with or without subchannels (Andre answered no, only writing), so why not C2 ?

EDIT : third solution, this CD has a repeatable error and gives different repeatable CRCs regardless of wether C2 is on or off.

Very interesting! I am glad you posted here, westgroveg.


I have never encountered this problem myself so far.
Some time ago I started doing a test WITH C2, after each of my 'normal' rips (secure mode, test+copy, NO C2). It doesn't take much time, and in some time ( = 100 rips or so), I'll post my findings here.


To whom it may interest:


About: Test+Copy in SECURE MODE : Overkill or not?

About 100 rips done, several CRC mismatches happened. So, by using Test+Copy, we can spot errors that EAC would otherwise not remark. Surprise?
For most people: yes!
For some people: not really --> In a previous thread (link: see further), it was *theoretically* figured out that this could happen, we only didn't know how big the chance was (Pio could refer to a theoretical calculation which said the chance of getting a CRC mismatch for a CD is somewhere between 0.5 - 1/100000000000..., which doesn't say much - we had no test results at the time... well that has changed now.)

I think I can say now that the amount of failures you can expect if you don't use Test+Copy, is a few % of all CDs. (Figures from a lot of other people who use Secure mode and Test+Copy, seem to confirm this conclusion.

Note#1: For this kind of problem, re-extracting the track always helps (the CRC mismatch is gone...).
Note#2: A CRC mismatch is often not an audible error.

I think this is a nice conclusion for a discussion opened a few months ago here
Thanks to everyone who contributed

liekloo,

When you say "a test WITH C2", you mean with the box "Use C2 information for error correction" checked, correct? Not just with the box, "Drive is capable of retrieving C2 error information" checked, and the other unchecked? It's not made completely explicit in the thread that you referenced, and I want to be sure I understand your tests.

I must have missed the conclusion or you didn't answer if it's overkill or not. No Test&Copy gives failures on a few % of all CDs. But what about other methods in comparison? Do you have any figures at hand to prove what you said?

EAC C2 boxes discussion split here

No, not correct, but it is my bad: I have been a bit lazy I'll explain :
Like many other people, I used "C2" as an abbreviation for "Drive is capable of retrieving C2 error information". The other feature you mentioned ("C2 for error correction") should not even be used!

(Yes, some people use it, but these are people who misinterpretet what this function does. Pio calls it an 'experimental glitch remover' and has said several times that we'd better use 'Deglitch.exe' than this experimental feature)

Clarification:

The conclusion was: Using 'Test+Copy' (instead of just 'Copy') is not a waste.

On a few % of all disks, we seem to get CRC mismatches (visible as a '#' in the 10th column of EAC, instead of 'OK'). You can see that as a warning: EAC says " extracted twice the audio, and I got two different results." This means there is a chance of 50% that your extracted audio is not a perfect CD copy. Solution: rip again in Test+Copy, and see if this times the CRCs match. If so, now you can be 'sure' that the CD copy is perfect.

Suppose you had used 'Copy' instead of 'Test+Copy', then you would never have remarked this failure of EAC, and have an imperfect CD copy.

One person (Tigre) said he got '#' on 10% of his rips (1 in 10!). The average is less: a few % I have the impression. If I had to do an educated guess, I'd say 4 - 5%. This is not thát much, but *much* more than anyone had expected!

You could say I tested EAC 'copy' versus 'test+copy', both in secure mode. About figures: I can give figures for myself (5 times '#' on about 100 disks). I can't give figures for other people, I have to believe what they tell me. But they all more or less experience the same thing. Also good to know: The total amount of rips done is hundreds, maybe a thausand (enough for a valid conclusion, but I have the impression that 50 rips is already enough to make valid conclusions on similar topics. Can anyone confirm this impression?).

Agreed



This high depends on the drive of course so unless you test it on a wide rage of drives all this shows is the C2 capabilities of the tested CD-ROM drive. It would be interesting to test the drives that have showed at www.cdspeed2000.com to have 100% accurate C2 information.



No. That is the argument of T&C being a waste, it could very well mean that the error occurred in the same position on the test & then also on the copy, I think the only way to be sure the two copies are bit exact would be to do a wav compare (It would be good if EAC had an option test, copy & compare).

I also would consider burst mode with T&C because no attempt of error correction is peformed so there is little room for errors.

-Ripping secure no C2 cache
-Test and copy
-Performing a wave compare

...are three identical things. The only differences are physical (speed, rereads, seeks...)

It is possible for 2 consecutive rips to produce matching T&C CRCs that are different from each other. It's rare, but it mostly happens when something obstructs the data from the laser (dust, f.ex.).

It's very likely to happen when a drive does not support C2 but the option is still enabled in EAC. The track quality might even be 100%, as shown by the log, but it's a sure sign that the drive that is instructed to perform C2 correction cannot reliably flag the data as "in need of some serious C2 treatment" and does not correct it properly as a result.

It's much more common to rip a CD which is already in its dying stages and come up with mismatching CRCs that are different every time you rip. These are the CDs that the best C2-capable drives (namely the Plextor PX-W1210A, off the top of my head) will be able to salvage the most accurate data from (as much as possible). With other drives you might have to slow down the reading speed to be able to avoid skips in those positions.

What westgroveg describes is the most common situation. It's very possible that both drives do not correctly flag and correct common C2 errors and the only reliable way to rip this CD accurately is to use EAC without C2. It is also possible, though, that the rip made with C2 enabled is the correct one, if your drive is one of the reliable C2-capable drives.

What you should do is rip the CD with the second drive and enable C2. See what the CRCs are and report here.

If you specify the 2 drive models, we could have a more educated guess.

Thanx for that seed, this has yet to happen to me but I read a past thread at the EAC forum where someone claimed this happened, they said C2 had failed & told what I have described & I thought to myself how can he be sure it was C2 that failed & not EAC's non C2 mode?

I have found EAC to fail (CRC mismatches) with C2 off on a few CD's with my Plextor but yet to find a C2 enabled rip to fail.

-Non C2 - CRC mismatch
-C2 - Errors detected, unrecoverable
-Plextools - Detected & recovered the errors

Of course these are results for one particular drive

In your place, I would "wave compare" the two extactions before jumping to any conclusion. We still don't know if you got errors or offsets.