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| Posted by | Jan S. |
| Posted on | 21/05/05 21:49 |
Conclusion:
As demonstrated by these few tests, anything can happen: sometimes the CATS and the drives agree and sometimes they disagree, sometimes the CATS can read a disc while the drives fail and sometimes it's the other way around. And the worse the quality of a disc is, the more differences you will likely see between all test results.
But as explained before, this is perfectly normal, since PI/PO plots not only show media quality but also the efforts of a drive to play a given disc: for instance, if a drive has very good mechanical and optical parts you will get fewer errors but if it uses cheap parts you will get more errors, all this with the same disc.
To summarize the differences we saw between CATS and drive measures, let's define 3 terms:
- Consistency illustrates the deviation obtained by multiple tests on the same disc with a given testing device. CATS are more consistent than drives because the results are repeatable, and several CATS machines will also give more consistent results than several drives of the same brand/model.
- Accuracy corresponds to the precision of the measurement system. For instance, on disc 6 KProbe reports a PIF of 209 (which should actually be 208) and on disc 4 CDSpeed reports a PIE SUM8 of 2360. The measurement accuracy of CATS is higher than the one of drives, because they are specifically designed to be measurement tools, while the alternative are software tools and consumer drives running on a PC architecture. For instance sampling errors, bus lags, driver conflicts are not problems which will disturb CATS measurements. Furthermore, the hardware parts of the CATS are precisely calibrated to match the measuring requirements defined in the DVD-ROM specification, which also contributes to its higher accuracy.
- Correctness is something absurd, which corresponds to a popular idea that each ECC block of a disc contains a precise number of PI/PO errors, and that measurement tools try to find out this absolute value. Let's repeat it one more time: PI/PO errors are not on a disc. PI/PO errors are the result of a calculation and they depend not only on the disc but also on the drive and on many other physical parameters, thus no PI/PO value is more correct than another. Just like PC drives, CATS will show slightly different results each time you run a test on the same disc, and none of them is wrong : they just correspond to what the error correction block calculated at that particular time.
CATS machines are definitely very useful for professionals, because they give a lot of technical information and can perform more accurate and consistent measures than consumer drives. On the other hand, CATS machines still use drives and limits defined in the original 1996 DVD-ROM specification, thus as time passes its reports differ more and more from the performances that modern drives can achieve, as illustrated by disc #4. Therefore what should matter to an end user are the tests he does by himself, with his own drives and his own media, in the recording and playback conditions he plans to use. And if you choose carefully the media and recording speeds which are best for your burner, you have a good chance to increase the compatibility and lifetime of your discs, which are the final goal of testing.
You may discuss/comment this article below or in this forum thread.
Update: Added a letter from AudioDev to clarify on advantage of CATS machines compared to the use of consumer drives for quality testing.
We would like to thank AudioDev, Plextor Europe, Erik Deppe and the author of Kprobe for their comments and help on this article.
There´s a reason for standards and specifications. It doesn´t matter, that there are many drives which outperforme a 1996 standard DVD ROM drive, if the one you have to use somewhere else doesn´t.
It´s great, if my new burner handles even discs, which reflecting to the standard, are completly f* ->aehm<- messed up, but if my lame notebook drive or the SA DVD Player or the 5 year old installation DVD ROM in my server can´t, it doesn´t really help me.
The specifications and standards are well known and I´m pretty upset, that the manufacturers don´t give a sh*t. If future players can´t play today´s discs, the customer has to worry.
Feel that manufacturers are not doing the R&D, but rather foisting incompetent and unreliable technology onto the buying public - I have decided against going hard drive or Disc for my camcorder. Can only afford one in my lifetime, so am going backwards to DV tape.
I also know many people who are so confused and have heard negative things about new technology such as unrelaibility, incompatability, and lack of longevity- no to mention that with so many avenues to go down, sales people do not know a lot anymore and conflicting sales views confuse the public even more.
It is time that the retailers told the manufacturers - NO - give me products to sell that will please my constomers and I know of at least one major large shop that specialises in Entertainment systems that refuse to sell anybodies DVD recorders due to the problems aforementioned.
This technology has been released too early and the manufacturers do not even know enough so their help lines are often of little help or incorrect advice.
Furthermore to have your pics put onto disc at great cost (commerciallly) and then find that a few years after, some of those pics are lost with more degrading quickly over time- I htink that perhaps the old ghastly VHS tape may be better for longetivity especially with consumer copied material.
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