High scanning speeds = lower errors?

vbimport

#1

A few members have recently brought this topic up. It’s not a new topic, but I thought it might be interesting to have a thread devoted to this.

Issue: Scanning PI/PO at higher speed produces lower error rates.

This seems to contradict common sense, but it’s not a new thing, nor is it specific to any particular drive. Some drives will exhibit a “preference” for reading at a particular speed, sometimes a particular discs will do this while others will not.

My best opinion on this is that you usually do not see this on “well-burned” discs, or at least the differences are much less pronounced. If a disc has “acceptable” error rates at a higher speed, but “unaccaptable” rates at a lower speed, you should assume that it’s not a good disc. Although it may play/read well enough in the short term, it probably should not be relied on to do so in the long term.

In the past, some folks have noted that 4x CLV scanning seems particularly prone to showing higher error rates, but again this is almost always on discs that are “marginal” in burn quality.

Any way, I made a small page with 2x, 4x, and 8x scans on both my 401@811 and my 1213(TDK) drives so you can compare the results.

Here’s the page All 6 scans are done on the same disc.

Everyone will not agree on the reasons for this phenomanon, but it’s interesting to explore I think. The 1213 drive seems to be especially fond of reading at 8x CAV.

So, should you opt for the scanning speed that produces the lowest error rates, or the one that produces the highest? Food for thought.

What quality is it in a disc that makes it exhibit this behaviour in a drive? Maybe jitter or tracking issues? Who knows, we don’t really have a way to measure these issues, nor is there any way to correct it short of replacing the drive or the media. Is it a “problem”? No, not really. Just something to be aware of, and one more good reason to avoid comparing scans from different drives, different read speeds, etc.


#2

In contrast to the scans I posted above, here’s a disc that exhibits very different behaviour at the same scan speeds:

This is more alone the lines of what would normally be expected with the different scan speeds.


#3

Here’s an example of what we all like to see in a burned disc: Again scanned at 2x, 4x, 8x;

There are subtle differences in the scans, but they are not significant differences. In fact the differences are all within the normal variations from one scan to the next, so you could scan the same disc 3 times at the same speed and see similar variations.

This illustrates my favorite point, that when you are looking at a high-quality disc, you cannot mistake it for anything else.


#4

Preach on brother Grimes maybe you should start a media reference forum and put all these good posts in it…and maybe mine here too http://club.cdfreaks.com/showthread.php?t=99405
but take off all the comments at the end of my thread and make them read only…etc.

my buddy futureproof has done this on the software side :wink:


#5

As one of the instigators, let me make a couple of contributions.

I don’t have much experience with DVD’s yet and it looks like I picked a bad drive to start with (I hope that better firmware will fix the SOHW-1213S). rdgrimes says that these differences tend to show up with marginal discs. I only have a few available, in most cases I don’t know which burner was used, so one problem is finding a known good sample.

Let me present a series of CD-Speed scans of what I thought was a good burn (I don’t know which burner was used). Both the SOHW-1213S and LTD163 didn’t slow down while scanning (12x and 16x) and I had no problems playing it. Here are scans @1x, 2x, 4x, 6x, and max



Initially, the behaviour is as expected- error rate increases with reading speed. But then there is the abrupt change when scanning switches from CLV to CAV at 6x. The drive seems to be a better reader at CAV! In fact, the results for 1x (CLV) and 6x (CAV) are pretty much the same. This threw me more a loop!

After looking at some further discs (I’ve spent much more time scanning than burning discs these last 3 days :frowning: ), things are a lot less clear. Another disc of unkonwn origin shows little differences between 4x and 6x (at low rates) and is apparently a “good burn” (similar to the previous post). A DVD+RW (drive can read these @4-9x CAV) looks a bit different (with no clear trend): here 4x and 6x:


I had a second SOHW 1213S available for a short time and found that the burning and scanning properties did not differ significantly (differences < factor of 2, trend similar).

One trend I did see was that the PIF-count increrased significantly @6x where the PI Sum 8 dropped, so a different stage of the error correction is active.

I will continue to do scans at various speed until I’ve convinced myself of the best way to go. At present, though it looks like rdg is right.

G


#6

Keep in mind that the 1213 will scan at 6x - 12x CAV in the “max” setting. Unlike it’s predacessors.


#7

Perhaps, making a sticky thread titled “Threads of Interest” or something like that? It will have the links to the threads like this one, the one Jamos is referring, and maybe others worth mentioning. I’m not sure locking such threads is a good idea, but it’s up to the mods.
Just my two cents.