Scans...

[Pain_Man]

Reading Chewie's recent post made some thoughts about scans congeal.

 

Here they are:

 

Going tangenital...

 

I'm beginning to wonder if there's any real efficacy to scans.

 

Something Lightning posted really made me think about it. He cautioned never to compared scans from one burner to the next.

 

I got to thinking about that. Why not?

 

If the metrics used by the scans are based on the same criteria then why should it matter what machine you're using? If the standard(s) are objective, then the results should be either exactly the same or the differences should be statistically insignificant.

 

Perhaps my lack of skills in this area is causing wild giggling as this is being read--and pls point out where I'm going wrong if I am.

 

But it doesn't make sense to me. Two thermometers, scales, speedometers, odometers, hygrometers, barometers, pick your instrument (and I realize all of these are much simpler than scanning an optical storage reader) should return nearly the same readings in the same condition.

 

Yet with disk scans, what gives?

 

I've gotten wildly different scans on the same disks in the same burner using different tools. Granted, the quality of the tool plays a huge factor and perhaps some are worthless.

 

To repeat, I really have to wonder: Are these scans really efficacious?

 

If they are, why the wild variations between different tools and different drives?

 

And why does there seem to be no correlation between image quality and scan numbers? If the scans are really to determine disc longevity, that question's answered. If they are supposed to determine image quality as well, then the question becomes an even bigger one:

 

Are we wasting our time running scans?

 

There's certain thngs I know a good deal about. Optical media isn't one of them (beyond the user level). I don't possess anywhere near the level of knowledge that Lightning or Shamus or Nic Wilson or Minty or any number of people who post here.

 

So if someone could explain, in relatively non-technical terms, whether or not I have a point, I'd really appreciate it. If its just my technical ignorance, I don't mind being told so (as long as its done nicely).

 

But I'm having trouble understanding the seeming discrepancies and whether they mean anything? Or whether its not the discrepancies but the scans themselves.

[LIGHTNING UK!]

I dunno but I tend to think about it in terms of driving a car.

 

Tell 2 people to drive 100 miles at a steady 80 MPH.

 

1 has a Ferrari, the other a VW Golf TDI.

 

They'd both reach the 100 mile way-point just fine but would use very different amounts of fuel.

 

So it's impossible to say 100 miles will use up X amount of fuel - FULL STOP.

But what you can say is 100 miles will use up X amount of fuel IN A FERRARI when driven at a constant 80 MPH.

 

All drives are different and have different reading abilities. That's why it's never a good idea to compare scans between drives - some are just going to report less errors as they're more able to read through problems areas that others may find quite taxing.

 

Hopefully that explains the drives side of things.

 

As for differences between programs... well in all honesty, there should be. The drive reports the data/values, the software just has to plot it on a graph.

Trouble is, (from what I've heard) some report in a different way to others and so it's the softwares job to try and find a common ground between ALL the drives - messing around using certain calculations to make them all seem the same. This is where the anomalies can creep in.

Again, every attempt to read the disc could end with a different result. A scratch that you couldn't get past on your first attempt may be invisible on the second... that's just drives for you!

[lfcrule1972]

Personally, I just them use when testing new media to give me a feel for the disc and media ID and to check the quality of disc backups that I need to keep.

 

I don't know enough about them to quote the pro's and cons but if I get quality ratings of 99% and low PI/PIF's I am more than relaxed about the backup.

 

I have had some bad burns with low quality and high PI/PIFs that my standalones can't play - I can't say where the line between playability/longevity and scan results lies but I think common sense tells me when to re-burn !

[chewy]

Scanning is a way to monitor integrity of a data bank, especially for idiots that built the bank with disregard for MID's. Tweaking cdspeed for more measure points in a quick scan is a good mass production tool.

Edited May 18, 2006 by chewy

[Pain_Man]

Thanks for the answer. It clears up a good deal.

 

The problem appears, if I understand that part of your explanation, that there really isn't a standard that everyone is using. Both the drivemakers and the software writers (of the scanners) seem to use differing criteria for their metrics.

 

If different drives are using different methodologies (right term?) then it goes a loooong way toward explaining the differences in scan results.

 

Thanks, again.

 

 

I dunno but I tend to think about it in terms of driving a car.

 

Tell 2 people to drive 100 miles at a steady 80 MPH.

 

1 has a Ferrari, the other a VW Golf TDI.

 

They'd both reach the 100 mile way-point just fine but would use very different amounts of fuel.

 

So it's impossible to say 100 miles will use up X amount of fuel - FULL STOP.

But what you can say is 100 miles will use up X amount of fuel IN A FERRARI when driven at a constant 80 MPH.

 

All drives are different and have different reading abilities. That's why it's never a good idea to compare scans between drives - some are just going to report less errors as they're more able to read through problems areas that others may find quite taxing.

 

Hopefully that explains the drives side of things.

 

As for differences between programs... well in all honesty, there should be. The drive reports the data/values, the software just has to plot it on a graph.

Trouble is, (from what I've heard) some report in a different way to others and so it's the softwares job to try and find a common ground between ALL the drives - messing around using certain calculations to make them all seem the same. This is where the anomalies can creep in.

Again, every attempt to read the disc could end with a different result. A scratch that you couldn't get past on your first attempt may be invisible on the second... that's just drives for you!

[Pain_Man]

Personally, I just them use when testing new media to give me a feel for the disc and media ID and to check the quality of disc backups that I need to keep.

 

I don't know enough about them to quote the pro's and cons but if I get quality ratings of 99% and low PI/PIF's I am more than relaxed about the backup.

 

I have had some bad burns with low quality and high PI/PIFs that my standalones can't play - I can't say where the line between playability/longevity and scan results lies but I think common sense tells me when to re-burn !

 

 

Nearly all of my scans have been of discs that I have had for anywhere from several weeks to nearly three years.

 

Oddly, the only 99% I've yet to get was from a disc that was 2 yrs old (!).

 

I can't say where the line between playability/longevity and scan results lies but I think common sense tells me when to re-burn !

 

Which is a good idea, one I've already adopted. I had one copy of a disc--the kid had destroyed the original when she was a good deal younger ("Look, Daddy, it flies!!!"). So I had but one copy, the backup. When I scanned it with DIP, the quality rating was 48%, with a gigantic, fat block of red in the top graph.

 

I managed to get a clean image and reburned it. The scan of the back ups back up was 95%+.

 

With DVD5s, if I can get a quality rating above 95%, I can live with that. With DLs, it if the number is above 90%, then I can deal.

[Pain_Man]

Scanning is a way to monitor integrity of a data bank, especially for idiots that built the bank with disregard for MID's. Tweaking cdspeed for more measure points in a quick scan is a good mass production tool.

 

 

 

The last sentence there, I'm not sure exactly whatcha mean by that. I've noticed that the faster the scan speed, the worse the results.

 

I scanned a couple of CDs at DW1655's max speed of 48x and the scans were a mess. I dropped it down to 16x and the scan was much better. My guess would be that the faster the disc is being read, the more likely false readings are to occur.

 

Just as you're more likely the miss words or misunderstand their meaning reading quickly than when reading carefully.

 

BTW, I'm sorry about the Falcon. I was dead broke and just couldn't keep the maintenance up on it. When the hyperdrive failed, I had to junk her . One of the hardest decisions I've ever had to make.

 

There's actually more to this than silliness. I had a '78 Olds Cutlass Supreme Stationwagon, the model right below the very biggest one. It was a metallic grayish, silverish color. My friends took to calling it the Millennium Falcon.

 

Seeing your moniker, brings back some very good memories. A lot of good times were had in that car.

[chewy]

there's a quick scan option with cdspeed but set the measure points for 50 in options under disk quality

 

frank soy trick from cdfreaks

 

or how to quick scan a 100 or so disks

 

leave scan speed at optimum/standard setting

Edited May 18, 2006 by chewy

[Pain_Man]

leave scan speed at optimum/standard setting

 

 

By "optimum" do mean fatest?

 

Because I've noticed that errors increase the faster the read speed and decrease when set to slower. I think this is why DIP only scans at 8x. Of course, I could be wrong...

[chewy]

optimum standard setting for scan speed is determined by the point where errors quit diminishing as you lower speed, the object is to get

a consistent scan at the fastest possible speed. 1X is best, but takes too long. It all a compromise.