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EAC secure mode test proposal, Testing its real accuracy
tigre
post May 3 2003, 14:41
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Edit : this discussion is splitted from this thread : http://www.hydrogenaudio.org/forums/index....=ST&f=20&t=8849


QUOTE (spoon @ May 3 2003 - 02:23 AM)
QUOTE
Well, actually errors 'always' (99.99...%) return different data for every new read.


How do you know that? it might be 60%, or 10%, because it cannot detect when the data is the same you cannot put a % on it. When AccurateRip makes its way onto EAC then you could put a percentage on it.

A. I haven't read anything about a "validated" percentage like this anywhere (wrong_samples_noticed_by_EAC_due_to_non-matching_results_on_re-read / total_number_of_wrong_samples).


B. This could be tested (volunteers appreciated) like this:

1. You need a (set of) reference .wav file(s). For this either rip a CD in perfect condition, EAC secure mode, ideally compare the CRC to a identical disk's ripped by someone else (cheers to AccurateRip wink.gif ) or choose some .wav files, burn them to CD-R and make sure you keep them unchanged on your HDD.

2. Take the CD(-R), damage it (e.g. different kind of scratches, caused by screwdrivers, sandig paper, ...; dirty fingerprints; draw lines with a thin marker on the data side; ...). Start carefully and try what happens in the next steps. If the disk turns unreadable and causes timing problems/sync errors in burst mode this won't work ...

3. Extract the damaged disk two times in burst mode resulting in a.wav and b.wav.

4. Do wave substractions (Cool Edit: mix paste - overlap - invert checked) r-a.wav=reference.wav - a.wav and r-b.wav = reference.wav - b.wav and a-b.wav = a.wav - b.wav
using Cool Edit or another wave editor capable of that - make sure that dither is disabled in this and the next steps.

5. We want to know how many samples have been turned "wrong" by damaging the disk, so we create a Cool Edit boolean operation like this: if a sample has been read correctly in a.wav, the corresponding sample in r-a.wav will be 0, otherwise something =|= 0. To find samples that are wrong in a OR b, we add r-a.wav and r-b.wav. To prevent errors here we multiply both files with themselves (Cool Edit: mix paste -> modulate), so all values are 0 (correct) or >0 (wrong). To prevent errors here (Cool Edit devides by 32768 after multiplying, so values -182<y<182 will turn 0 due to rounding) we amplify both .wavs by 100dB before. This will lead to 0 values = correct and 32767 values = incorrect (-> amplification by 100 dB makes all samples =|= 0 clip in 16 bit resolution). So the steps are:

5.1. Amplifying: r-a_100.wav = r-a + 100dB; r-b_100.wav = r-a + 100dB
5.2. Copy r-a_100.wav to clipboard and mix paste - modulate r-a_100.wav with data from clipboard, result: r-a_100m.wav; do the same with r-b_100.wav => r-b_100m.wav
5.3. Add (= Cool Edit mix paste - overlap) r-a_100m.wav + r-b_100m.wav = wrong_samples.wav


In the file wrong_samples.wav. we have now all 0 samples stand for correctly extracted samples in both EAC burst mode runs while =|= 0 samples (32767) stand for extraction errors.

6. Now first interesting thing to do IMO would be to have a look at the error postitions. Are there isolated wrong samples or do they occur as blocks / "bursts"?

7. Now we want to know how many of the wrong samples have gotten different values in the two burst mode runs so EAC secure mode would have detected them. For this we
7.1. apply steps 5.1 and 5.2 to a-b.wav resulting in a-b_100m.wav
Step 7.2.
7.2.1. Take a-b_100m.wav and apply Channel Mixer -> Full mix (L = L+R; R = L+R). -> detected_errors.wav
7.2.2.: multiply wrong_samples.wav with detected_errors.wav (Mix Paste Modulate) and substract the result from detected_errors.wav, resulting in the corrected undetected_errors.wav.


The result will contain 0 samples for correct samples and detected errors and 32767 samples for undetected errors.

8. Counting the Number of 32767 samples in wrong_samples.wav (W) and in undetected_errors.wav (O) will enable you to calculate a percentage of correctly detected errors: P=(W-O)/W

Have fun smile.gif

edit:
Additionally we could rip 3 or 4 times in burst mode instead of 2 times to find out if and how often Test & Copy in secure mode without C2 detects addtional errors.

And we could rip in secure mode, C2 enabled (if drive capable) to find out the "P" value for the drive's C2 detection.

edit2: changed some "?" to "=|=" which means "un-eaqual"

edit3:
I missed one thing: If in the 1st 2 reads an error occurs, the sample is re-read in both channels, no matter if the error was detected in one or both channels. So "undetected" errors in one channel are in fact detected if there's a detected error at the same postion on the other channel.

To take this into account in the test, step 7 is modified (see above).

This post has been edited by tigre: May 6 2003, 10:28


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tigre
post Jun 5 2003, 00:11
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QUOTE (Pio2001 @ Jun 4 2003 - 01:50 PM)
Tigre, it seems what you call extended reread is assuming that all errors in the rereading range are detected.


You're right. I just tried to find the errors that will remain undetected for sure ...

QUOTE
One should rip 16 different versions of the CD, and keep the samples that are 8 or 9 times the same as good, then see if they actually are.

tongue.gif ... because I'm too lazy to rip 16 more times - and do 15+ more comparisons. You're right: One should ... - but this "one" won't be me. wink.gif

QUOTE
In this case, your 99.8 and 97.4 % results are just upper bounds for the actual accuracy, because among the 1930 and 86 other errors, many will remain undetected after rereading, since they are consistent. The 80 % accuracy is then not unlikely.
Hard to tell without testing. I'd rather think that most of the errors are detected during 1st 16 re-reads (because of reduced speed and the finding I mentioned in the post before: in secure mode (C2 off, Drive caches checked) the same drive + same CD either give perfect results or report errors at bad positions - 10 trials, no undetected error).

QUOTE
These consistent errors would be just samples damaged beyond recovery. Each time they are read, an error occurs, and they are always interpolated, thus returning a consistent result.

The way I understand how audio CDs work, there's quite some damage necessary to get an unrecoverable error (C1 + C2 failing). So as several damaged = "unsecure" bits read in raw data are needed to cause an error (that makes the drive interpolate), it's rather unlikely that all of these bits are returned identically on several re-reads resulting in identical interpolation.

Whatever ... My conlusions so far:
- More tests needed
- Real life secure mode performs much better on error detection than my "simulation" for so far unknown reasons.
- It seems like Secure mode (C2 off, correct cache settings) is more secure in error detecting than Burst mode Test & Copy with CRC check.

This post has been edited by tigre: Jun 5 2003, 00:14


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Posts in this topic
- tigre   EAC secure mode test proposal   May 3 2003, 14:41
- - Pio2001   For this kind of tests, it would be much better to...   May 3 2003, 15:11
- - mrosscook   tigre, Your test outline is very interesting and ...   May 3 2003, 15:49
- - liekloo   QUOTE (mrosscook @ May 3 2003 - 03:49 PM)Tigr...   May 4 2003, 12:00
- - evereux   QUOTE (mrosscook @ May 3 2003 - 02:49 PM)Ther...   May 4 2003, 12:04
- - Canar   QUOTE (DrDoogie @ May 2 2003 - 07:48 AM)QUOTE...   May 4 2003, 12:16
- - liekloo   QUOTE (evereux @ May 4 2003 - 12:04 PM)QUOTE ...   May 4 2003, 12:35
- - evereux   I have read a file can be manipulated to give the ...   May 4 2003, 12:50
- - Pio2001   EAC's CRC are 32 bits, thus there is one chanc...   May 4 2003, 13:50
- - mrosscook   No, the point I'm trying to make doesn't h...   May 4 2003, 15:05
- - Pio2001   Yes, you're right. From experience, I think t...   May 4 2003, 19:44
- - Pio2001   I think it's sensible to assume that the first...   May 4 2003, 19:48
- - liekloo   QUOTE (Pio2001 @ May 4 2003 - 07:44 PM)Yes, y...   May 4 2003, 20:23
- - Pio2001   I don't think that their secureness is even si...   May 4 2003, 21:04
- - tigre   @All: Thanks for your replies, suggestions and att...   May 5 2003, 09:33
- - tigre   I started a test as proposed: The CD: VA - Stel...   May 5 2003, 09:39
- - DrDoogie   Tigre: 5 sounds good, I'll have a look at it l...   May 5 2003, 14:58
- - tigre   QUOTE (DrDoogie @ May 5 2003 - 05:58 AM)Tigre...   May 5 2003, 15:36
- - tigre   Test part 2 trying to take into account the amount...   May 6 2003, 11:44
- - DrDoogie   I think I lost track of the argument somewhere alo...   May 6 2003, 14:12
- - Pio2001   An error is given by the difference between the re...   May 6 2003, 15:49
- - tigre   1st: You ask a question, so I'd appreciate if ...   May 6 2003, 16:06
- - Pio2001   Tigre, your result is interesting. How does look l...   May 6 2003, 16:20
- - Pio2001   It would be interesting to know how your drive beh...   May 6 2003, 18:41
- - tigre   Thanks to Pio2001 who provided detailed informatio...   May 27 2003, 11:35
- - Pio2001   Wow ! This gives (1-20/10000)*100 = 99.8 % acc...   May 27 2003, 16:30
- - Canar   QUOTE (Pio2001 @ May 27 2003 - 07:30 AM)Wow ...   May 28 2003, 05:42
- - tigre   QUOTE (Canar @ May 27 2003 - 08:42 PM)QUOTE (...   May 28 2003, 08:32
- - tigre   I tested the same scratched CD with another drive:...   May 28 2003, 15:26
- - DrDoogie   QUOTE I'd rather say: We knew before that EAC ...   May 28 2003, 16:00
- - tigre   You're right about swans ... I just havn...   May 28 2003, 16:31
- - Pio2001   Saying EAC is not perfect, and not using it becaus...   May 28 2003, 18:44
- - Pio2001   Tigre, it seems what you call extended reread is a...   Jun 4 2003, 22:50
- - tigre   QUOTE (Pio2001 @ Jun 4 2003 - 01:50 PM)Tigre,...   Jun 5 2003, 00:11
- - Pio2001   I think I'll perform some little tests myself....   Jun 5 2003, 11:13
- - tigre   QUOTE (Pio2001 @ Jun 5 2003 - 02:13 AM)About ...   Jun 5 2003, 11:26
- - DrDoogie   QUOTE (Pio2001 @ May 28 2003 - 09:44 AM)Sayin...   Jun 5 2003, 15:05
- - Pio2001   I agree with you. But the reason for which EAC was...   Jun 5 2003, 19:50
- - kdo   QUOTE (tigre @ Jun 5 2003 - 11:26 AM)- It see...   Jun 7 2003, 21:44
- - Pio2001   QUOTE (kdo @ Jun 7 2003 - 11:44 PM)(Well, exc...   Jun 8 2003, 00:06
- - kdo   QUOTE (Pio2001 @ Jun 8 2003 - 12:06 AM)QUOTE ...   Jun 8 2003, 14:21
- - Pio2001   No doubt, no doubt !   Jun 8 2003, 23:39


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