Interpreting PI/PO error scans

vbimport

#1

In this thread I’ll try to explain that, if you do not want to know all the technical details, then just skip this first post and go to the next post.

Technical details:

Download the ECMA 267 Standard for DVD-ROM, the ECMA 337 Standard for DVD+R/RW and the ECMA 338 Standard for DVD-R/RW at http://www.ecma-international.org if you want to look at the standards for yourself. Here is some data from the ECMA standards (same for DVD-ROM, DVD-R/RW and DVD+R/RW):

Random errors:

A row of an ECC Block that has at least 1 byte in error constitutes a PI error. In any 8 consecutive ECC Blocks the total number of PI errors before correction shall not exceed 280.

Here we see what a PI error is defined as a row in an ECC block having 1 byte or more containing errors. And that the sum of PI errors in 8 ECC blocks after each other should not exceed 280 PI errors.

But what is a row and what is an ECC block? Again we refer to the ECMA standards. We do not copy and paste everything but if interested look in the ECMA standards.

A row is 182 bytes long where the last 10 bytes contain PI (Parity Inner) information. An ECC block is 208 rows long where the last 16 rows contains the PO (Parity Outer) information. This gives us a maximum possible PI error amount of 208 errors per block and for 8 blocks after each other this sum is of course 8 times higher giving a maximum possible amount of 1664 PI errors. In practical use we have found that a disc with 1664 PI errors is unreadable.

According to our test the specified max PI sum of 280 for good discs seems to be a good guideline, as a few readers have problems reading discs when the PI failures is over 300 and many players starts to have problems when the PI failures reaches 600 and most players have problems with discs exceeding 900 PI errors or more.

But what are the PO errors that K-Probe reports? Actually the PO errors that K-Probe reports is the Parity Inner uncorrectable errors, meaning errors left after PI correction. Only the ECMA 337 standard describes the Parity Inner uncorrectable errors. So how is a Parity Inner uncorrectable error defined? Here are what ECMA 337 states:

“If a row of an ECC Block as defined in 13.3 contains more than 5 erroneous bytes, the row is said to be “PI-uncorrectable”.”

In theory an ECC block may in the worst case have 208 PI uncorrectable errors since every ECC block is 208 rows long. But the ECMA 337 standard goes further and specifies the max amount of accepted PI uncorrectable errors allowed on a good disc:

“- In any ECC Block the number of PI-uncorrectable rows should not exceed 4.”

This is where K-Probe gives us problems as for PI errors it have to be set to a PI/PO sum of 8 ECC blocks to show results that compares to the standard, but for PI uncorrectable errors (Called PO in K-Probe) the PI/PO sum have to be set to a sum of 1 ECC block.

A guideline is to calculate the Parity Inner Uncorrectable errors to 8 ECC sum, which is max 32 (4 x 8) Parity Inner uncorrectable errors, but now we can’t be sure if one of the 8 ECC blocks exceeds the specifications. But if the result exceeds 32 PI uncorrectable errors we know that at least one block have more than 4 PI uncorrectable errors. But if the PO error amount is between 5 and 32 there may still be a block that exceeds the standards.

But what makes a disc unreadable? A PO uncorrectable error will make the disc unreadable, but K-Probe does not display the PO uncorrectable errors.

Also these standards are probably when the disc is scanned at 1X reading speed.
So to get results directly comparable to the standards you have to scan a disc twice at 1X reading speed:

1 time with PI/PO sum set to 8 ECC to get a result comparable to the 280 PI errors per 8 blocks standard.
1 time with PI/PO sum set to 1 ECC to get a result comparable to the MAX 4 PI Uncorrectable (Called PO in K-Probe) per block standard.

But to make it faster and easier we have “relaxed” the scanning requirements a bit compared to the standards as you may read in the next post.

Maybe this got to technical detailed and you are wondering what to look for out of the errors that K-Probe report? Look in the next post :wink:


M DIsc Burner. What one to buy?
#2

For the following recommendations to be true K-Probe must be set to 8 ECC PI/PO sum while scanning and preferably scanned by a Lite-On DVD-Writer (in other words NOT a DVD-ROM or Combo!).

Use this as a guideline for good discs:
PI (Parity Inner): No larger areas on the disc should exceed 280 PI errors, do not worry too much about high single spikes that exceeds 280.
PO (Parity Outer): No larger areas on the disc should exceed 32 PO (actually PI uncorrectable) errors, do not worry too much about high single spikes that exceeds 32. (Note that this is not completely correct according to the standards, but is still a good guideline, read the first technical post if you wonder why this is not a 100% correct way of reading the results compared to the standards).

Notice that there are other aspects such as disc reflectivity, jitter, tracking errors and so on that also will affect the readability of a DVD disc – but for this we do not have measuring equipment available.

And another note is that we normally scan/recommend scanning the discs at 4X CLV speed since this saves time compared to 2X/2.4X and 1X scanning and still offers CLV reading, but by lowering the speed to 2X(DVD-R/RW)/2.4X(DVD+R/RW) or 1X the amount of reported errors may drop on some discs.

Also using Nero CD/DVD-Speed to do a transfer rate test with a picky DVD-ROM (JLMS XJ-HD165H for example) and see if the reading speed drops is a good indication of the quality of the disc.

In the next post we will show several examples of K-Probe scans.


#3

Original pressed DVD-ROM disc, Baldurs Gate DVD-ROM:

As we could see there is a high spike for both PI and PO, you should just ignore such high spikes, as they are probably just a small reading glitch and not a real error on the disc. When ignoring the high spike we could see that the PI errors top out at around 37 errors that are far from the 280 PI errors standard. The PO errors tops out at 4 that is also very good.

Original pressed DVD-Video disc; Indiana Jones and the last crusade. Notice that only the first layer is scanned:

As we could see there is again a high spike for both PI and PO, you should just ignore such high spikes, as they are probably just a small reading glitch and not a real error on the disc. When ignoring the high spike we could see that the PI errors top out at around 18 errors that are far from the 280 PI errors standard. The PO errors tops out at 7 that is also very good.

An excellent scan of a DVDR disc ( Taiyo Yuden 4X DVD+R disc written with a Memorex Dual-X DVD-Writer):

Most likely you will never see such an excellent scan as few discs in combination with even fewer writers is able to produce such outstanding results. PI at max 8 and PO at max 4 is far from the 280 PI max and 32 PO max that we recommend as the max values.

A very good scan of a DVDR disc (BeALL 4X DVD-R written by Plextor PX-708A):

A very good result with PI max of 24 and PO max of 5. This is what you should expect from the best discs on the market. Also the error level is constant which is very good as well.

An acceptable scan of a DVDR disc (RitekG04 4X DVD-R written by Memorex Dual-X):

With a PI max of 104 and a PO max of 7 these discs is still far from exceeding the standards and should not cause any trouble. Again the error level is pretty constant, which is fine.

A marginal scan of a DVDR disc (VDSPSAB01 4X DVD-R written with Memorex Dual-X):

With a max PI of 303 and a PO of max 20 these discs is marginal and slightly exceeds the standards and may cause reading problems in a few devices. Will probably still work good in most devices though, but now it’s time to start to worry about the results and consider changing to another disc brand.

A bad scan of a DVDR disc (Creation DVD-R 2X written with plextor PX-708A):

With a maximum PI of 837 and a max PO of 66 this disc exceeds the standard by a long shot. But still some good players may be able to read the disc. But you should definitively consider changing media if this is how your scans look.

A very bad scan of an unreadable DVDR disc (Princo 4X written by plextor PX-708A):

The PI maxed out at 1456 and the PO maxed out at 1262. Way beyond the standards and probably needless to say but this disc is totally unreadable after the first 15% in all devices we have tested the disc in.

Comments/suggestions is welcomed.


#4

I think this is as good a place as any to discuss some of the problems people report with PI/PO scanning. A common report is that a disc will scan good (or bad) one time and the next time it will scan the opposite way, with the differences being fairly extreme.
We saw much the same thing when we first started scanning CDRs for C1/C2 errors. The situation does not appear to be all that different than it was then.
The discs that cause this weird behaviour are almost always discs that are somewhat marginal in burn quality. Those discs that are excellent in burn quality do not do this, and likewise those discs that are truly crappy do not do this.
Lowering your reading speed for the scan may eliminate some if not most of the discrepancies between scans.
One way to try to confirm a discs relative read-ability, as OC mentioned, is to use CDSpeed or DVDInfo to run a read-speed test (transfer rate). If the drive has trouble reading the data, it will slow down during the test, and that will show on the test graph. Discs with relatively minor reading issues can cause a slowdown in those tests, so it’s a pretty good way to confirm that there may be trouble.

DVDRs have enormously compressed data compared to CDRs, so even slight problems with tracking or laser calibration can cause high error rates. I also suspect that poor burn quality can induce tracking isses that may vary quite a bit from one scan to the next.
One thing for certain is that there are a lot of differing opinions on this issue, as many opinions as there are people.
But I think it’s worth repeating that we do not see inconsistant scan results on the really good media/burns nor do we see it on the really crappy ones.

Other theories have been offered that poor disc balance can induce these on again - off again scan results. I suspect that this may be true, as would slightly out of round or warped discs, uneven dye distribution, etc., etc.

Even combinations of any of the above issues would contribute, considering the extremely low tolerances involved with DVD.


#5

Thanks again OC_Freak and rdgrimes. This is the best explanation of K-probe readings i’ve seen. I’ve actually saved this page to my K-Probe folder.


#6

PI/PO scaning with DVD-ROM drives
This topic must get raised at least once a week. So here’s our best answer:

Kprobe is designed to work with burners only. A number of it’s features will ONLY work on burners. It is possible to scan discs with LiteOn DVD-ROM drives, but not advisable.

DVD-ROM drives do not respond to the read-speed commands from Kprobe, so they will always scan at full speed. This is especially bad for DVDR scanning.

DVD-ROM drives do not appear to report the same types of errors as C1-C2 and PI-PO as the burners do. We do not know what they are reporting, but there does not appear to be any predictable relashionship between what gets reported on a ROM drive and what gets reported on a burner.

Many people do use ROM drives for scanning errors, and this is certainly better than not scanning at all. But you have to be aware that your scans cannot be compared to scans done in burners. So your only use for the scans is to compare one disc to another as you are searching for the right combination of media and burn speed in your own burner.


#7

Anyone who has been scanning CDR’s for a while knows that the higher the read speed, the higher the error rates will be. The same is true of DVD’s. In fact, it seems that this is even more true with DVD.

A number of people have noted specifically poor scan results at 4x read speed, and sometimes lower rates at full speed. (8xCAV). this phenomenon is due to several things which I will not go into here, but what is important is that this does not occur on well-written high quality media. Normally, you will see gradually increasing error rates as scan speeds increase. When scanning at full speed, (CAV), you will see low erorrs at the start and a curve of higher errors near the end. This is due to the increasing linear velocity of the disc in CAV mode.

The main thing to remember is that you can scan at any speed you like, as long as you do not compare scans with different read speeds. It’s also important to note that the higher quality a disc is, the less difference you will see at different scan speeds. In other words, if error rates vary wildly from one speed to the next, this is a clear sign of a poor quality burn.
In the end, a disc only has to meet DVD specs at 1x read speed, and this is clearly adequate for movies. But if you can acheive low error rates at higher speeds, this is more likely to produce discs that last a long time and have fewer playback problems or compatability issues.


#8

here are two kprobe scans of 2 burns (4x rated ricoh discs) at 6x with TDB’s rpc and rip lock free non beta firmware for the nec2500a and scanned with 851s:
link1
link2

they look very good with pi avg of .5 or so and po .02 or so.

now here are the scans of the same two discs done on 812s:
link3
link4

The pi average shot up by over 10x, but the po was pretty much consistent. Any ideas?

Here is a scan (by 812s) of they same type of 4x disc burns at 8x with the beta6 by Herrie:

link5

I suppose it still looks good but im disappointed with the huge difference between scans by 851s and 812s. Any ideas?


#9

KProbing, unfortunately, is not very accurate of a way to determine errors.

Take, for example, one discussion that took place in the LiteOn forum. Someone with a 451@851 did a scan of a disc and then rescanned the same disc, on the same drive, only this time, he undid the mod and changed the drive back to a 451. Very different readings came out of that. In any case, your 812S scans are well within the acceptable limits, even if they are 10x as high (well, with you have a PI avg. of 0.5… ;)), so I wouldn’t worry about it very much if I were you.


#10

tx for the reply code65536.


#11

[QUOTE]Originally posted by OC-Freak
[B]For the following recommendations to be true K-Probe must be set to 8 ECC PI/PO sum while scanning and preferably scanned by a Lite-On DVD-Writer (in other words NOT a DVD-ROM or Combo!).

Got a question: How Shoud be K-Probe set to how many ECCs ??? Because i have a Lite-ON LDW 851s and this is a Combo

Thank You For Replying


#12

Originally posted by Assass1N
[B][QUOTE]Originally posted by OC-Freak
[B]For the following recommendations to be true K-Probe must be set to 8 ECC PI/PO sum while scanning and preferably scanned by a Lite-On DVD-Writer (in other words NOT a DVD-ROM or Combo!).

Got a question: How Shoud be K-Probe set to how many ECCs ??? Because i have a Lite-ON LDW 851s and this is a Combo

Thank You For Replying [/B]

Liteon 851 is not a combo as to what he was referring to.
He is referring to the DVD/CDRW combo drives (ie read only dvds).
your liteon 851 will work just fine with kprobe.:wink:


#13

Originally posted by commissioner
[B]here are two kprobe scans of 2 burns (4x rated ricoh discs) at 6x with TDB’s rpc and rip lock free non beta firmware for the nec2500a and scanned with 851s:
link1
link2

they look very good with pi avg of .5 or so and po .02 or so.

now here are the scans of the same two discs done on 812s:
link3
link4

The pi average shot up by over 10x, but the po was pretty much consistent. Any ideas?

Here is a scan (by 812s) of they same type of 4x disc burns at 8x with the beta6 by Herrie:

link5

I suppose it still looks good but im disappointed with the huge difference between scans by 851s and 812s. Any ideas? [/B]

from what ive seen between my 811/851 and my 812 is the 812 seems to be alot more accurate on error rates. I would trust your 812.


#14

Originally posted by Jamos
Liteon 851 is not a combo as to what he was referring to.
He is referring to the DVD/CDRW combo drives (ie read only dvds).
your liteon 851 will work just fine with kprobe.:wink:

My Lite-On reads CDs also as i read at web site of a shop where i bought it its says that this is proffesional Combo Drive

Dont know why the QUOTE didnt work properly :sad:


#15

Ok i noticed why QUOTE didnt work

If some1 could reply to this post above wolud be very nice coz i think this Lite-On is a combo drive - its burning DVDs and CDs and also Read them both !!


#16

I answered you…

YOUR DRIVE IS FINE TO RUN KPROBE ON!
He was referring to DVD reader/CD read writers as combo drive definition (like my LTH1618H)…not yours which is a DVDRW/CDRW.
your drive technically is a combo drive also but thats not what he was talking about.


#17

All right, time for some brain picking. I’ve been making ALOT of Kprobe scans, and some graphs leave me in doubt as to the quality of the discs. Now Rdgrimes did an excelent job of laying out Kprobe and explaining how to analyse its results in a overral fashion, but there are certain graph quirks which I’m not sure are good or bad. To illustrate, I’ll use a previously posted pic :

Should I worry when I see a solid block of low level PI errors like that? Some of my scans give me a solid red block on 1, almost solid on 2 and quite a few PI errors on 3. I take it this would qualify it as a “regular” disc, working but not impressive… ?


#18

A quick read of this thread would have revealed this:

PI/PO scaning with DVD-ROM drives
This topic must get raised at least once a week. So here’s our best answer:
<snip>
DVD-ROM drives do not appear to report the same types of errors as C1-C2 and PI-PO as the burners do. We do not know what they are reporting, but there does not appear to be any predictable relashionship between what gets reported on a ROM drive and what gets reported on a burner.

Many people do use ROM drives for scanning errors, and this is certainly better than not scanning at all. But you have to be aware that your scans cannot be compared to scans done in burners. So your only use for the scans is to compare one disc to another as you are searching for the right combination of media and burn speed in your own burner.

Hope this answers your question.


#19

I did read that. That wasn’t my point.

My point is, I get similar scan results from a LiteOn SDHW-812S (which is not a DVD player, as you know). Solid or very thick PI errors up to 1 and 2. Good, bad, no problem?



#20

I love this technical stuff with the graphs and all. I’m currently having a problem with some -RWs and want to isolate the problem. What’s a good freeware/shareware to use if your burner is not a LiteOn? (I have a Panasonic 521)

Thanks