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):
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 contain 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-8 errors. In practical use a disc with 1664 PI-8 errors is unreadable.
According to our tests the specified max PI-8 sum of 280 for good discs seems to be a good guideline, as some readers have problems reading discs when the PI-8 errors is over 300 and most players starts to have problems when the PI-8 error level reaches 600 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
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 what makes a disc unreadable? A PO uncorrectable error will make the disc unreadable, but K-Probe does not display the PO uncorrectable errors.
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.
Easier explanation on how to read the test results.
Maybe this got too technical, and you are wondering what to look for in Kprobe reports?
Use this as a guideline for good discs:
PI(Parity Inner): No larger areas on the disc should exceed 280 PI-8 errors, do not worry too much about high single spikes that exceed 280.
PO(Parity Outer): No large areas on the disc should exceed 32 PO-8 (actually PI uncorrectable) errors, do not worry too much about high single spikes that exceed 32.
And as always; lower is better
And look at the reading curve, a slight slowdown at the end is probably nothing to worry about, but huge bumps and slowdowns are not good.