Important Defects in Plextools 2.17 - Part II

A second problem I have with PlexTools 2.17 is that the DVD “jitter” measurements are almost completely useless because:

(1) There are no indications what the scale is or (more important) where zero is.
(2) The jitter graph readjusts itself vertically, jogging up if the graph threatens to go off the bottom of the scale. So no two graphs can be compared!

True, the shape of the graph can be seen, i.e. how whatever it’s measuring varies over the recorded area of the disk. But what clue do we have as to the absolute values being displayed?

It’s as if Plextor wanted to include some kind of Jitter Graph but didn’t want to reveal too much!

Look at the attached image for an good example of this vertical shifting of the jitter graph. My experience so far is that any jitter graph begins in the lowest major division of the vertical scale. If the graph then heads upward, no problem, the graphs remains stationary (Fig.1).

But look what happens if instead the graph heads south! Fig.2 shows 4 snapshots taken while a disk was being read. As the graph tends lower, the graph shifts upward three times! So … are these high or low values? Does the graph always start off in that lower-left corner and gets tweaked if it goes lower? What is the display strategy? Where is zero? (Ignore the downward spikes; thay are harmless artifacts of my setup.)

I feel this is a nearly-useless display. It could have been done properly, but wasn’t. Is anyone at Plextor thinking this through?

I agree that it would be more useful to get the average jitter per sampling point, plotted to a fixed scale with proper units (even if this can be misleading to those who think that the values are ‘on the disc’).

To me it appears that Plextor only wanted to show the relative changes in jitter with that graph.

That is still possible even with the moving of the graph data around.

However, as you correctly state, it totally loses the possibility to compare one scan to another scan, because the scales could be from totally different points of the axis.

regards,
halcyon

The issue of jitter is that it should not exceed 35ns. This is hard to measure with a graph.

The graph is set up on a scale of Low to High. The key for measuring jitter is that no matter where the measurement starts, the display should be a fairly level line as the disc is read. It can drop slightly or rise slightly, but there should be no dramatic rise or drop indicating an area of the disc with more jitter than another area. I’ve seen jitter displays that are fairly level until about mid point, then the level rapidly climbs. The error rate of these discs reflects the jitter display, with more errors in the higher areas of jitter.

If your PI/PO is low through the disc, jitter has to be good. If your PI/PO increases toward the outer edge, measure the jitter. If the jitter is high also, try lowering the speed on the next burn. Try different media and stick with what works for your drive.

The 716 uses a histogram like the CATS tester to display T3-T11 and T14 in its new TA test (not available for the 712). this is a better indication of disc quality.

Wow, bob11879,

this is really interesting! How do you know all this stuff? Did you already
put your hand on a 716? :wink:

Regards,

ET

I am eager to work with Plextool’s new TA … IIRC, the graph is generated from HF read signal analysis … we will see how it works.

The only thing that bothers me … I will have to buy a 716A although my 712A is only 4 months old … :bow:

bob11879,

Thanks for the additional info.

Can you refer to the spec that says jitter (which jitter, btw?) should not exceed 35ns on a dvd disc?

AFAIK, DVD specification does not have hard limits for pit land transitions.

I know the spec for CD, but I wasn’t aware of the limit for dvd.

I’ve read that data-to-clock jitter in reading should not exceed the 8%/9% limit of the timing window (DVD-R/DVD+R respectively).

I still don’t know how to read the Plextools 2.17 (on PX-712A) jitter graph. I have absolutely no idea what the scale is on the right. The units surely are not ns nor are they percentage values of the timing window :slight_smile:

friendly regards,
halcyon

PS You didn’t happen to write under the handle ‘bobhere’ in EAC forums?

Sorry about the quick post with no info…

The TA description is in the posted spec for Q check and in PTP 2.17. Time analysis will give a histogram…and TA will do T3-T11 and T14. Maybe I do have the CD-R and DVD jitter specs mixed up…eitherway, the left hand scale is jitter (low/high) and the right hand is beta. I think beta maximum is +/-0.8–the scale is +/- 0.5. For my 712, when I check with good media, the jitter is a slim line that is fairly flat across the display…some up and down, but not much. If I use some crappy media, the display can be all over the place.

The shots above show beta at about 0, where it probably should be, but shows really crappy jitter. My first thought is try with a few other brands of media for comparison and then do some screen shots.

Bob,

your opinion of Plextools Pro / 712 jitter display is similar with mine.

I think the relative changes in the jitter graph are the only usable indicator of jitter quality. Still, it’s hard to distinguish how much of a relative change is ‘too much’.

Also, there are no specified limits for T3-T11+T14 jitter (data-to-data) on a dvd disc. Also, I find it quite odd that the drive would be able to actually measure that, when the data-to-clock jitter is what really matters.

regards,
Halcyon

PS Afaik the timing window (clock cycle) on a dvd disc is 38.25ns, so 35ns is a limit on a cd disc, not dvd.

Low is 3t. It is how far you are from that causes issues on readability. The high scale is 11t. this can be obtained by hitting the help button on the test.

The jumpiness of the jitter graph is also due to a bug in the program when you minimize it and then restore it when it is running. the graph line will jump up or down.

Works fine for me, did u uninstall previous version and reboot before installing?

so plextools graph scales cant be adjusted by hand? =/

You can manually adjust the scale of every type of Plextools graph, EXCEPT the Jitter graph.

You have to click Preferences and type the desired value …