In this thread Iâ€™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.
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 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:
â€œIf a row of an ECC Block as defined in 13.3 contains more than 5 erroneous bytes, the row is said to be â€œPI-uncorrectableâ€.â€
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:
â€œ- In any ECC Block the number of PI-uncorrectable rows should not exceed 4.â€
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 canâ€™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 â€œrelaxedâ€ 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