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What exactly does CD Speed scan disc/quality check measure?

Burn baby burn!

Postby cfitz on Sun Feb 23, 2003 4:27 pm

jase wrote:To say "brand X when written at Y speed on brand Z writer caused N C1 errors, this is therefore a bad burn" is actually an erroneous statement. A C1 error count for a certain type of media actually tells us very little about the state of the recorded media on its own, and should not be used as a black and white argument that brand X doesn't work well with writer Z. True?

I wouldn't call it an erroneous statement, but it is incomplete. In general you are right that one measurement alone does not make for a definitive characterization of the compatibility of media brand X with writer Z. But we can still get useful information from such measurements.

I think spath has the right idea here. You need to look at the entire system, including the writer, the medium, the reader and the conditions under which the medium is written and read when considering the meaning of C1/C2 error measurements. All of these affect the measured error counts, but that doesn't mean any one measurement is more or less valid than another. It just means that the conditions under which the measurements were made were different. And since we do want to be able to write and read discs under varying conditions (e.g. high speeds), all of the measurements are of value. But you do need to be aware of the different conditions that underlie the results in order to make meaningful interpretations of the results.

Also, keep in mind that, even though CD Speed, WSES, CD Doctor, etc. are great tools and we are very grateful to have them, they can't characterize a disc at the physical level of detail required to pass judgment on the "absolute" quality of a disc. No tool available to us as general consumers can do this. Thus, we can't specify the absolute quality of media X, and, in fact, it doesn't even make sense to try. At best one can say media X performs at some level under some conditions.

However, this doesn't invalidate the measurement of C1/C2 errors in an effort to characterize media and media/drive combinations. Certainly relative assessments of media quality are fair game. We may find that media X does consistently better than media Y when tested under identical conditions on the same drive. We can then say that media X is superior for those conditions on that drive. And we may find that media X does consistently better than media Y under a number of different sets of testing conditions. Then, we can expand our conclusion to state that media X is generally superior to media Y (keeping mind that there may always be exceptions for specific test conditions).

Having said all that, I would say that measuring a disc at lower read speeds probably does tilt the balance more towards showing errors due to faults in the written disc and away from showing errors due to the reader. The measured errors are still result of the interaction between the two, but lower read speeds likely deemphasize faults in the reader. Still, the best advice probably remains:

ErikDeppe wrote:The results of such tests should be seen as relative comparison data.


cfitz

(Apologies to those who have read part of this post before. I lifted a portion of this post from an old post that I wrote, because I believe it is germane to this discussion.)
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Re: OK now, who can explain this?

Postby cfitz on Sun Feb 23, 2003 4:37 pm

jase wrote:
HazMat wrote:After I burned the first disk at its rated speed (24x) on my Asus CRW4816 I did a Disk Quality Check with CDSpeed v1.02, as I do every time I buy a batch of new disks - the results indicated just short of a coaster - thousands of C2 errors
<snip>
Hours later ... When I returned home, I tested again the "bad" CD: only 35 errors with the CRW4816, none at minute 10, and no errors (zero) with the CD-S500, both drives read the CD at full speed...


Possibly slight warping caused by the media being very warm when you test-read it? TBH I'm not sure. Fornet media is dodgy at the best of times. I had one batch in 2000 which was some of the best budget media I've ever used (all 100 discs still perfect, with low C1 error count -- about 0.6 average when read on a LiteOn at 52x) but other discs from them have been abominations!

I have also seen such behavior occasionally - a disc that shows a number of errors when tested immediately after a burn shows fewer after being allowed to rest. Jase's hypothesis regarding heat as the cause sounds like a reasonable possibility. It wouldn't be unreasonable for the heat of burning to affect the disc, the reader (assuming it is the same drive used to write the disc), or both. The exact mechanism is beyond me, but there are certainly several possibilities I can think of:

1. disc warping (as noted by Jase)
2. increased noise in the detection electronics (heat increases electrical thermal noise)
3. "curing" of the dye as it cools

cfitz
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Postby rdgrimes on Sun Feb 23, 2003 5:29 pm

- a disc that shows a number of errors when tested immediately after a burn shows fewer after being allowed to rest.

Don't forget the effects of a hot drive. I've had drives that when hot, would return twice the error rates as when cool. Inadequately cooled cases/drives are not good.
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Postby HazMat on Sun Feb 23, 2003 5:44 pm

Here's what I found out, and if someone feels like repeating this sort of test, please do :)
The only difference between the first test (imediately after burning) and the second test (hours later) was that in the first case I had Nero Burning Rom loaded (doing nothing, just sitting idle in the background). Keeping this in mind, and testing further, I noticed that having Nero loaded in memory somehow influences the result of CDSpeed Disk Quality Check (it makes CDSpeed return errors if there are none under normal testing circumstances i.e. Nero is not running). Further more, exiting Nero will not make CDSpeed return accurate information again, it needs a reboot to do so. I can replicate the test anytime: I just scan the disk a few times says zero errors every time, then I start Nero and regardless if I exit Nero immediately or I leave it running, CDSpeed shows enough errors to make you wanna throw the disk out of the window. I'm asking you, is this a normal behaviour? I mean, if Nero interferes with CDSpeed and make the Disk Quality Check return invalid results, perhaps other 3rd party programs can invalidate the results of CDSpeed...
On the other hand, there is a chance the above may be absolutely normal to happen, due to the nature of the programs (both are accessing the ASPI, or some other reason) - my appologies in this case.

My software configuration:
Nero Burning Rom 5.5.8.0
CDSpeed 1.02
Win98SE
ASPI 4.71

Other thing: Nero Info Tool reports system ASPI 4.71 and nero ASPI "not installed" under Win98, but under Win2K Pro it says system ASPI "not installed and nero ASPI "Installed and working OK". I have not conducted any test under Win2k, but I will.
How can I install both nero ASPI and system ASPI under these OSes?
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Postby cfitz on Sun Feb 23, 2003 6:22 pm

Sorry, HazMat, I can't duplicate your results. As I would expect, I get the same results whether or not Nero is open. Nor can I think of any plausible reason why having Nero open (but not accessing the drive) would have any effect on the measurement results reported by CD Speed. Perhaps Erik will have something to say about the behavior you are reporting.

As for ASPI, neither Nero nor CD Speed needs a system-level installation of ASPI. Nero installs its own version of ASPI to avoid conflicts with other ASPI layers, and CD Speed can use Nero's ASPI layer. You might want to try uninstalling and reinstalling Nero, and also updating to the latest version, if it appears that Nero's ASPI layer is not installed properly. Perhaps that will clear up your issues with CD Speed as well.

I have both Nero ASPI and Adaptec ASPI 4.60 (installed via Force ASPI) on my W2K box. I recommend using Force ASPI if you want to install a system-level ASPI layer.

cfitz
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Postby spath on Mon Feb 24, 2003 3:38 pm

> OK, therefore we arrive at the following conclusion: To say "brand X when
> written at Y speed on brand Z writer caused N C1 errors, this is therefore
> a bad burn" is actually an erroneous statement. A C1 error count for a
> certain type of media actually tells us very little about the state of
> the recorded media on its own, and should not be used as a black and
> white argument that brand X doesn't work well with writer Z. True?

Bottomline is : a cd system is very complex, so if you want to test a
specific part of it you must always keep all other prameters fixed,
otherwise comparisons can lead to wrong conclusions. So for instance
if your goal is to compare media compatibility with drive X, you should
burn several discs of each brand with drive X, same test conditions and
read them back with the same drive X (or Y), same test conditions : then,
comparing average Cx results will give you an idea of the best brand for
your drive. That's about the best indication you can get without special
equipment.
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