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Topic: Some questions about C2 (Read 5536 times) previous topic - next topic
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Some questions about C2

Everywhere I've looked that shows you the "proper" method for ripping a CD says that you gotta disable C2. Ok, I can live with that. But I just have a couple questions...

1. What's the REAL risk with C2 error? Does that mean I'll get the wrong CRC? And if so, won't AccurateRip let me know?
2. Why is extraction faster with C2 turned on? I averaged around 5x on an 80min CD (Tool - Lateralus) with C2 off, but ~7.5 with it on. The last track finished at 12.7 with it off and 15 something with it on. So why the difference? I would think that, if anything, it'd be much slower having C2 turned on...

Some questions about C2

Reply #1 –
>What's the REAL risk with C2 error?
EAC might not catch every error.

>Does that mean I'll get the wrong CRC?
If an error goes undetected, yes.

>Won't AccurateRip let me know?
Only if the exact same pressing of the disc is in the database and was ripped correctly.

>Why is extraction faster with C2 turned on?
Without discussing synchronization, EAC only reads the data once when C2 error reporting is enabled.

Some questions about C2

Reply #2 –
That doesn't make sense. If C2 reporting is turned ON, then EAC might not catch every error? I don't get it. I always thought that with C2 on, you just might get false positives for errors and that will mess up the CRC.

Quote
C2-errors are divided into three sub-types:

E12 = one bit defective, 100% correctable
E22 = two bits defective, 100% correctable
E32 = three or more bits defective, no correction possible

So it would make sense for a drive to only report the E32 (uncorrectable) C2-errors?
Yes, but unfortunately this depends on the manufacturer of the drive.
Some drives report all C2-errors, some different combinations of them.

Since we don't know which drive reports which types, the C2-feature is useless, because it might give false positives.


Quote
Without discussing synchronization, EAC only reads the data once when C2 error reporting is enabled.


And it reads it twice (guessing) when error reporting is disabled?

Some questions about C2

Reply #3 –
I'm afraid you're giving far too much weight to the text you are quoting (which I have previously read, btw) concerning how EAC behaves with many drives.  I am not saying that false errors can't get reported, I'm just saying that errors can get missed, which is why so many people recommend not using the option.

Now depending on what you read, the blame may either lie with the drive not properly or fully reporting E32 errors, or EAC's ability to catch all of them.

Yes, in the event that C2 is disabled, EAC reads everything at least twice (assuming the cache setting is correct for whatever drive is being used).

Some questions about C2

Reply #4 –
Quote
I always thought that with C2 on, you just might get false positives for errors and that will mess up the CRC.

I don't think false positives will mess up the CRC, because C2 is only used for error detection, not correction. If an error is detected, it just uses the same re-read method as when C2 is off (C2 pointers aren't used during re-reads).

Some questions about C2

Reply #6 –
Same as the chances of getting a consistent error ? 

edit - (Well, less than...)

Some questions about C2

Reply #7 –
>False positives won't mess up the CRC unless the area is already prone to get (re)ripped incorrectly.
>What are the chances of that happening?

More common than you would think, the CD has to be return some kind of data, if the drive interpolates then it is highly likely the same bad data would be read twice (even a T&C).

Some questions about C2

Reply #8 –
But I'm talking about a consistent error in the same specific area where a CU is reported for data that was correct.

Whatever the chance of it happening, it is certainly less than the chance of just getting a consistent error, as Cosmo pointed out.

But as is the case with consistent errors, as you eluded, they can happen without the user's knowledge.  Thank goodness you've given us AccurateRip!

Some questions about C2

Reply #9 –
so if i've extracted anything out of this thread, it seems to be the message that the C2 option really doesn't make any difference one way or another, yeah?

edit: by that i mean off a clean disc that (theoretically) should be completely "perfect" (error-free).

Some questions about C2

Reply #10 –
If the disc is in excellent condition, I'm not even wasting time in secure mode. First I rip in burst mode and verify with AccurateRip. If there are less than two discs in the AccurateRip db to compare with, I run a test rip and compare the test and copy CRCs. Only tracks that don't pass AR (2 or more positives), or CRC checking, go on to be ripped in secure mode.

In secure mode, without AccurateRip to back up the results, I'm very hesitant to trust C2 detection (even though it seems to work pretty well on my drive). But if the disc has 2 or more entries in the AccurateRip db, I'll gladly give it a try with C2 enabled for the speed increase.

Some questions about C2

Reply #11 –
Instead of burst mode in EAC, I would use secure mode with c2 - it is effectively burst mode with some error checking.

>C2 option really doesn't make any difference one way or another,

It does, and is useful in detecting errors, it is EACs implementation of c2 means you have to trust that c2 is implmented very well as no other error checking is done.

Some questions about C2

Reply #12 –
So Spoon would you recommend it be kept on? Apparently my drive (Lite-On LTR52246S) supports it. It's just that every music torrent site upload guide recommends that it be kept off. Personally I'm inclined to keep it on as it speeds up rips and it's for my own personal use anyway.

Some questions about C2

Reply #13 –
I know my name isn't spoon, but I'll just state the obvious -

Quote from: hushypushy on
It's just that every music torrent site upload guide recommends that it be kept off.

Because:
A) they don't use AccurateRip
B) as spoon said, "you have to trust that c2 is implmented very well as no other error checking is done"
C) they don't use AccurateRip

EAC only tests if C2 error reporting is supported by your drive, but can't certify it's accuracy

Some questions about C2

Reply #14 –
Oink advocates the use of AccurateRip for checking drive offset; one would assume they endorse its use for CRC checking (but don't require it). Their guide quietly mentions that you shouldn't use C2 but doesn't show a reason.

Is there a place to go to check which drives support C2? I have a fairly popular drive, I bet someone else has already gone over this...

Some questions about C2

Reply #15 –
Most Lite-On drives can even report C1 errors IIRC, which is useful for scanning disc quality. I can't promise that the error reports will be correct with your model, but I've had good results so far with my drive (LiteOn SOHR-something, can't remember the exact model number right now.)

Does EAC try to re-read on C2 or CU errors?

Some questions about C2

Reply #16 –
hushypushy:
cdfreaks.com might have information regarding C2 accuracy for your drive.  What is your drive, BTW?

Reasons why not to use C2 have been given here in this very topic.  C2 has been discussed at great lengths in this forum by many people who are intimate with the topic.  A search will be fruitful.

MedO:
Not with V0.95.

Some questions about C2

Reply #17 –
ooh, my bad, I swore that I already listed it (but didn't bother to check..). I have a Lite-On LTR52246S and a SOHW-832S. The latter is horrible for ripping in my experiences but the former has done me well.

Thanks for the google search, I used the internal search and that didn't go well because you can't search for a 2 letter string.