detail information

Writing the Dual layer disc:

As you probably know already, the supported DVD+R Dual layer writing speed is 2.4x. This is our first meeting with DL media so we were kind of nervous to write it, but this is how we did it: First we took our original Three Kings DVD-Movie disc (The largest DVD-Movie we had; 7.83Gb) and created a ISO image with DVD Decrypter. Then we wrote the ISO Image with Nero with the following settings:

And after holding our breath for about 45 minutes the disc were finished successfully:

Yes, 44 minutes and 39 seconds is a very long wait, but it did finish successfully so it's time to take a look at the created disc:

As we could see the booktype of the disc is DVD+R DL, we think that some writers will support bitsetting for DL media and write them with DVD-ROM booktype for higher compatibility. But as we all know, the drive and firmware we have is not yet finished. Let us take a look at some K-Probe test results followed by reading results with various drives.

Write quality:

You should first notice that this is not a scientific and professional way to test the discs. But according to our testing done in recent months, we would conclude that there is a clear link between the quality reported when scanning the disc and the playability of the disc in different devices. Also notice that different drives report different amounts of errors. K-Probe was designed to work with Lite-On DVD-Writers. So we recommend using a DVD-Writer from Lite-On, in this test we use a Lite-On SOHW-832S DVD-Writer, as already said; remember that scans done with a Lite-On DVD-ROM or Lite-On combo drive can't be compared with the results obtained with a Lite-On DVD-Writer. Also remember that different PI/PO ECC sum settings along with different reading speeds in K-Probe will affect the result, we use these settings;  PI (Parity Inner) set to summarize 8 ECC blocks, PO (Parity Outer) set to summarize 1 ECC block, reading speed: 4X CLV (Constant Linear Velocity). Setting the PI sum to 8 and the PO sum to 1 will give a result that we may compare to the standards for DVD+R/RW and DVD-R/RW.

But what is a good scan? That is a discussion that we don't think will end soon, as different drives report different amount of errors, some players is more picky about media than others, and so on. But as a comparison we present you with a scan from a pressed dual layer disc:

This scan shows the result from a pressed DVD-Video disk (Indiana Jones and the last crusade). Notice the error jump when shifting to the second layer (the error level actually drops from the end of the first layer to the beginning of the second layer).

If you read below you will see that the pressed DVD-disc are well within the standards.

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 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 means that when the PO sum is set to 1 the maximum error value should not exceed 4. The theoretical maximum value for PO errors is 208 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.

And another note is that we have scanned the discs at 4X CLV speed, 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. We scanned at 4X CLV due to lower speeds taking to much time.

To see if there is a connection between the reported amount of errors and readability of the discs we also include the reading curve from a JLMS XJ-HD165H DVD-ROM that seems to be pretty easy affected by the quality of a written disc.

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 larger areas on the disc should exceed 4 PO-1 (actually PI uncorrectable) errors, do not worry too much about high single spikes that exceed 4.

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.

The quality results.

First we will scan the disc at 4x, as usual:

We could see that there is an error spike when switching layers, but beside this it seems ok and is within the standards. Just to see if it matters we scanned the disc at 1x speed as well:

The difference is minimal, but the error spike at the layer change is gone.

Now it's time to see how the readability of the disc is, first we tried it in the BenQ DW830A:

As we could see there are no problems reading the disc. We also played it with WinDVD and there were no playback problems. Let us try it in two DVD-ROM drives, first the JLMS XJ-HD165H:

A slight dropdown near the edge of the disc (near the layer change) but not to bad and there were no problems playing the DVD with WinDVD. Time to try it in a Toshiba SD-M1612 DVD-ROM:

The drive aimed at reading the disc at 16x (we are using a speed hacked firmware), but quickly slowed down and totally failed when trying to switch to the second layer. To bad this was the case for most of the drives that detected the dual layer disc. And most DVD-.Writers is totally unable to detect the disc. Look below for a table showing our results with different drives.

*Able to read the first layer but failed when trying to read the second layer.

As we could all see the compatibility with various drives is very low, only the two DVD Writers able to write dual layer media were able read the disc, and only one other drive were able to read it. Yes we know that you are wondering about Set Top DVD-player compatibility. Unfortunately we did only have one player available to test with and that is a Denver DVD-188DIVX, cheap but pretty new and officially supports both DVD-R/RW and DVD+R/RW media. The result? Unable to detect the disc, after insertion it just claimed 'No disc".

That was all we had for you this time, but we will soon have more tests and information available for you, let us summarize our feeling about the DVD+R DL format so far.

Positive:

• Fits 8.5Gb data
• Possibility to backup DVD-Movies without loosing picture quality or additional features.

Negative:

• Low writing speed of only 2.4x.
• Questionable compatibility with various devices.

Conclusion:

The dual layer DVD+R writing format doesn't seem to be a good option yet as the compatibility of the written discs is not very good. But this entire article is based on a pre-release drive along with pre-release media and we think and hope that things will improve in the future. Hopefully most manufacturers will be able to implement booktype changing for dual layer media, hopefully making them more compatible with various devices, especially Set Top players.

And we hope the writing speed will be further increased to at least 4x in the future, bringing the recording time down to about 30 minutes per disc. But we do see the clear benefits of having 8.5Gb space available per disc; it will make it possible to backup your favourite movie collection without loosing quality or features.

Notice that this article is done very fast and a more complete article/review will be posted later when the final firmware and media versions arrive. One thing is for sure: You will hear more about the Dual layer DVD+R format in the coming weeks and months, so there is definitively a lot to look forward to.

You may discuss/comment this article below or in this forum thread.