Is this statement in the FAQ wrong?

Hey all,

I was looking at the Kprobe 2 thread, looking for the proper setting for speed. In a screenshot they showed 4x, so that’s what I used.

This is my result at 4x:

Then I read the Interpreting C1/C2 Error scans thread. I found this quote, and decided to run the full scan again at Max.

The other thing you need to pay attention to when looking at these scans is the scan speed. Speed = more errors. Most people will scan CDR/RW discs at max speed. but if you encounter a disc that has problems, lowering the read speed will make it easier to scan accurately. The read speed is also included on the image near the middle of the top portion.
Be wary of scans that are done at low speeds, as they will almost always show low error rates, and may not tell you much about how the disc will perform outside the scanning program.

Here is my result at Max, same disc.

I don’t get it. My results are completely opposite what the FAQ said they would be. Instead of getting more errors at Max speed, I got only about 10% of them.

IMO, Lower speed = Higher Accuracy.

Oh yeah, this was burned with a Lite-On LDW something or other (been a long time since I swapped the firmware) patched to SOHW-832S.

And yeah, as the image name says, it was a disc to disc burn, at 24x.

Dan O.

The recommended scan speed of 4X is for DVDs. The section on C1/C2 errors refers to CDs which are scanned at MAX. DVDs have PIE and PIF errors.

BTW, Liteons scan DVDs at 4X while BenQs scan at 8X. NECs are not good for scanning but those that do anyway scan at 5X.

And you are correct in thinking that lower speed means higher accuracy. As it takes forever to scan at 1X most of these speed conventions are a compromise between accuracy and efficiency. As none of the scans we do are a real measure of actual errors on a disc, it is also important to be consistent. It is hard enough to compare two different 4X scans but is an exercise in futility to compare a 4X scan to a 16X scan.

I would have to disagree with the statement, that scanning is more precise at lower speeds. IMHO scanning at different speeds merely present a different view of the quality of a disc, and one view is not better or more precise than another view.

If you need to compare scans however, they should be made at the same speed.

As to why the number of C1 errors are lower when scanning at Max speed this doesn’t surprise me at all. Modern drives are designed to read at high speed, so when the speed gets too low they sometimes don’t read as well. I see the same thing with my Plextor PX-712A drive: CDs are usually best read at a 14-32x or 17-40x CAV speed, for some discs it is better to read at a slower speed (<14-32x) but for other discs it is better to read at the high speed. Some CDs show this as an elevated C1 level at the start of the disc when scanning at 10-24x CAV, and look much better when scanned at a higher speed.

You can think of scanning speed in this way: If you ride a bicycle, does it become safer the slower you ride? (No, if you ride too slow it will be very difficult to keep your balance). Or how about flying an airplane - does it become more stable the slower you fly? (No, there is a slowest possible speed and if you go below that the plane will stall).

Interesting analogy but I think you are wrong. To take your own example, at what speed on your bicycle will you be more able to accurately observe the scenery? Burners scanning are not considering stability; they are watching the scenery go by. If you were correct we should see MAX scans providing fewer errors instead of more, and this is not the case.

Quote:
Originally Posted by DrageMester
You can think of scanning speed in this way: If you ride a bicycle, does it become safer the slower you ride? (No, if you ride too slow it will be very difficult to keep your balance). Or how about flying an airplane - does it become more stable the slower you fly? (No, there is a slowest possible speed and if you go below that the plane will stall).

Interesting analogy but I think you are wrong. To take your own example, at what speed on your bicycle will you be more able to accurately observe the scenery? Burners scanning are not considering stability; they are watching the scenery go by. If you were correct we should see MAX scans providing fewer errors instead of more, and this is not the case.

Both very interesting. I think its a combination, If you fly too slow you fall from the sky or in the case of riding a bike fall over. but if you are flying or riding too fast you can’t see what you are passing by. :slight_smile: :slight_smile: :slight_smile:

I think you are both right.

If you are riding your bike too slow, it’s unstable and you fall off.
Too fast, the bearings in your wheels overheat, expand & explode out of their cases & your wheels fall off.

Hint This actually happens … if you don’t have enough lubrication …

I never said that the drive reads best at its maximum speed, I merely said that it doesn’t necessarily read better at the slowest speeds, and that sometimes it reads better at the higher speeds.

In other words, the drives usually don’t do their best at the extremes of their speed range - not at their slowest speed nor at their maximum speed.

And yes, I do have scans of CD-R burns that scan better at 32x, 40x or 48x than they do at 24x. And I even have examples of DVD burns that scan as well at 12x as they do at 2x, although this is very rare.

EDIT: Corrected 16x scans to 12x scans in last paragraph

Here’s a CD-R that scans best at 17-40x in my Plextor drive. Note that the C1 levels are elevated at the beginning of the 10-24x scan which suggests, that the drive reads this disc better at higher than 10x speed.

The disc was burned in my laptop burner (Matshita UJ-840S).

[ol]
[li]PxScan at 10-24x speed[/li][li]PxScan at 14-32x speed[/li][li]PxScan at 17-40x speed[/li][li]PxScan at 20-48x speed[/li][/ol]





Here’s one of the very rare examples of a DVD+R scanning as well or even marginally better at 5-12x CAV (maximum) speed compared to at 2x CLV speed.

The disc is a Verbatim 16x DVD+R (MCC 004) burned at 16x in my NEC 3500.

[ol]
[li]PxScan at 2x CLV (including Beta/Jitter)[/li][li]PxScan at 5-12x CAV[/li][/ol]



I have carefully thought about your analogy, and I don’t think it is a good one.

If you ride a bicycle, you need to have a certain speed in order not to fall - you cannot keep your balance if the bicycle is stationary (unless you’re an acrobat). If you ride down a steep hill at 50mph it definitely won’t be very safe either. This is my analogy to CD/DVD burning - the burner doesn’t do its best at the extreme low or high speed.

Your analogy of watching the scenery from a bicyle isn’t a very good one, because you can stand still and watch the scenery without any problems at all, but a CD/DVD drive HAS TO BE MOVING the laser over the disc to read anything at all - the reading is inherently a dynamic process, not a static one, so it doesn’t work at its best if the speed is too slow.

Regardless of which analogies are best, I think that my scans above show that slower isn’t always better, and sometimes it’s worse.

Let’s stop thinking with analogies for a second :slight_smile: A drive calculates
PI and PO errors for each ECC block as it decodes data, so speed does
not matter there. Next the drive has to send data to the PC, and there
the slower you scan, the more values you will be able to collect for a
given disc, which could be seen as more precision.

However, scanning at lower speed can also give higher PI/PO values,
for instance because the motor is optimized to spin at higher speed
(the same reason why it is not recommended to burn audio CDs at 1x
on modern drives). In this case, your data are less precise, because
you added some influence from the drive to the PI/PO errors due to
the disc’s condition.