Originally posted by john
I cannot prove anything, there are only 2 utilities that can measure C2 % Accuracy.
I think it is still possible that a drive:
1. Reads an error from the disc (physical or data level)
2. Does not report (via MMC) C1/C2 error as having happened
3. Does not correct C1/C2 error data
4. Conceals the error in the corresponding audio file
Or is this kind of scenario implausible in your opinion?
I had a Hitachi GD-7500 dvd-rom drive that couldn't give
C2 error flags via the MMC command set and the concealment
sometimes worked (although mostly not :)
errors from the drives that comply to the MMC standard. Many other drives may support *perfect* but with unknown commands to the software authors so are un-usable for us!
I understand. I think it's the manufacturer's loss if they do not
provide information on their special commands.
The software used by people in the future will be free and non-propietary anyway, so no-one will trust manufacturer X, even if they claim (but can't achieve under the MMC command set) a 100% C2 accuracy.
Nobody will believe drives that need special programs to perform well and the superiority of which nobody can verify for themselves :)
I'm glad you are making this thing clear.
The whole meaning of this paragrath was to explain that ALL drives can report C1/C2 errors (!) but not all drives have the same C2% accuracy. Can you see the difference?
Yes, I get it now, but I think the paragraph is a little difficult to understand :)
Do you have a test disc for which you KNOW (ie. have the manufacturer's specs) that how many C1 errors and C2 errors it has?
These would have to be data level (not physical layer) errors on the disc.
It would be easy to test the drives then to find out if they can spot all C1 and C2 errors and report them back accurately.
The problem with physical level errors (scratches), which can lead to C1/C2 errors is, that they are hugely dependent on many factors such as servo, laser, amplification, sensor, etc performance. And the results can vary (AFAIK) from one reading to another (using the same disc and the same drive).
Hence, it becomes very difficult to measure which drive reports all C2 errors accurately, unless we know how many errors there are on the disc, right?
Hmm..We made several attempts to create the disc. I cannot show you how to do it, but just try to be gentle with the scratches!
Ok, thanks. Will do.
However, I'm not sure I'm convinced that the EAC DAE quality test with the hand made test is the best approach to determining C2 accuracy... More like servo/pickup performance :)
I would say that if you also look later on, the C1/C2 errors reported from various LiteOn drives, the LiteOn LTR-52246S series seems to be the best for reading C1/C2 errors. Of course someone may argue with this, meaning using the drive that returns the lower error rate, instead of using the drive that returns the worst error rates (that disc would be un-readable in that reader)...
This was exactly my point ("someone may argue...").
With a test disc that has errors on the physical level of the disc (data is encoded/pressed/burned on the disc error free, but the disc has physical scratches/smudges/dirt/markings), a perfect reader should fulfill FOUR conditions:
A) report back as few errors as possible, which would imply superior reading of the disc and error free reading of the data, even under difficult conditions (this only applies if condition B is met also). In CD Speed test, as low count of C2 errors flagged by the drive as possible (zero).
B) report back ALL errors that it encounters (i.e. effects of physical level problems that the reading mechanism cannot circumvent, resulting in corrupted data, which may or may not be corrected by C2). In CD speed test this should be as high C2 accuracy as possible (100%)
C) Correct as many bits of contiguous lost data as possible (according to my reference books, the C2 error correction performance of all drive is not similar. Hence not all can correct E31 errors that some drives can).
D) Do all of the above while maintaining the highest possible reading speed (i.e. 38x or somesuch).
In fact, this is initially what I thought your test from page 99 onwards did, but I don't know what kind of a test disc (Abex TCD-721R) is: are errors on data layer, physical layer or both?
Also, I don't know how to actually test the C2 error correction capability of the drive's internal circuits, unless one uses a data layer error test disc, which has progressively difficult errors on the data level (one such contiguous error per track). This disc would have to be ripped one track at a time and see how far (how many bits of contiguous data) the internal C2 implementation can correct.
Do you know if anybody makes such a test disc?
BTW, If the test disc you've used has errors on the physical layer, then how can the program calculate the amount of C2 errors missed and C2 accuracy, when the amount of C2 errors read is dependent on the a) chance, b) phase of the moon, d) quantum probability, and e) the pickup/servo of the drive?
That is, a drive may flag and report X or Y number of C2 errors on a disc that has scratches.
How many C2 errors did it miss, if it reported X in total? How many did it miss, if it reported Y total?
I don't understand. Sorry :(
No the test results were posted only after tested one time. You are right that we should have done the tests several times and averaged, we hope to update the article soon, free time is very limited as you
Please don't take it as a criticism. I was just asking how you did it. You're efforts are REALLY appreciated. I would have done this myself, if I knew how :) YOu have taught me so much new things. And I know personally how time consuming testing can be (I've done testing for several dvd-rom drives with EAC and the CD-Check test disc myself).
The numbers taken as the CD Doctor software measured (and reported from the drive).
Yes, but I don't understand if a high or low is better and why :(
CD-Check? I don't understand
Comparing drives / Procedure (on page 106):
"The Total number of the test discs was eight (8):
Does that mean the 'Cd-Check' test disc by Digital Recordings?
I've used that myself as a crude physical level error test disc with DAE testing myself (don't have Abex discs, yet).
Yes we decided to use for now on, only Jitter test results. The main reason is that 3T Jitter measures the writing quality absolute, while C1/C2 errors may affected from surface problems (dust etc..)
Very good point. I don't exactly know what variables may change from burner to burner (with same media). If it's just land/pit jitter, then that's truly the ultimate measure.
I don't know, this would be difficult, we are not close [:I]
I know :) But there's always the postal service that can carry a test packet of 8 burned CDs quite cheaply <hint> :)
Will be used in future pressed "protected" Audio discs. If you read the information, it speaks about improvement during the mastering process. We won't see that such technology in personal recorders i imagine
Actually even a burner is a 'mastering' device in a sense.
It gets PCM data, encodes it according to CD standard and then tries to control the servos and the laser as well as possible to ensure a proper 'master' (I'm using the word 'master' in quotation marks as the word is usually reserved to glass masters for CD pressing. Still, the basic principle are the same sans).
But I digress, yes... it looks like a combination of a copy control technology and 'improved audio' marketing device :)
Thanks for the Almedio link as well. I just got a reply today.
PS I noticed several minor technical inaccuracies and some proof reading stuff in the report. I could offer to help you on those, if you want