No flux transitions

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Copy Protection details

Postby mr.vince » Thu Nov 10, 2011 5:17 pm

I bet this would look different if read in another drive. This is purely unpredictable, and I guess will also look different if I use a HD disk...

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Re: Copy Protection details

Postby Dio » Thu Nov 10, 2011 6:45 pm

mr.vince wrote:Ok, coming back to this "strong DC erasure" thing. Recording theory says you can't record this unless you use a permanent magnet.

What's the difference between a permanent magnet generating 1T and an electromagnet generating 1T? I'll accept that this can't be recorded with a drive head and electronics, but I'm not sure that a magnetic field can care what its source is?

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Copy Protection details

Postby mr.vince » Thu Nov 10, 2011 7:01 pm

True. I was not precise there; you can of course. You will need a beast of a coil to generate the same field these modern permanent magnets generate.

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Re: Copy Protection details

Postby Hippy Dave » Thu Nov 10, 2011 7:56 pm

Some definitions, so that what is said is not misconstrued:

Flux -- Magnetic field lines. To see these, place a sheet of cardboard over a bar magnet and spinkle iron filings.

Flux Transiton -- Change in magnetic field strength.

Flux Reversal -- A flux transition that passes through the zero flux level.

Noise Floor -- Intrinsic noise level of media where a low level signal becomes unrecognizable due to the resolution of the media. An insufficient signal to noise ratio will cause erroneous bit changes when reading digital magnetic media.

Degauss -- To demagnetize. (eg. with high frequency AC on write head). Thus remanent magnetic flux is zero.

Magnetize -- To magnetize. (eq. with North pole or South pole on write head).

AGC -- Automatic Gain Control. Low level signals are amplified more than high level signals so that low level signals have the same amplitude as high level signals after AGC. AGC has an Attack and Decay, thus taking time to adjust to the new level (important). AGC connected to a magnetic read head will increase the amplification of low level signals (or lack thereof) which will boost the noise floor.

Erase -- To erase data from magnetic media. This can be done with a powerful North pole (permanent magnet or DC electromagnet), a powerful South pole, or a powerful AC electromagnet. Media erased with a permanent magnet or DC electromagnet is Saturated with Magnetic Flux (lots of constant, unfluctuating flux!). Lack of fluctuation in flux will produce no voltage (just the noise floor) in a read head regardless of AC or DC erasure.



DrCoolZic wrote:It is also interesting to note that we do not find any flux transitions below 3µs ???

This is likely due to the size of the read head gap.

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Re: Copy Protection details

Postby mr.vince » Sun Nov 13, 2011 11:29 am

Alright, here's a track that has sync, and then "flux reversal suppression" after this. This should result in no or very few fluxes showing up.

Preparing a business trip, so again... DrCoolZic... can you please make a graph? :)
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Re: Copy Protection details

Postby DrCoolZic » Sun Nov 13, 2011 6:30 pm

I have looked at the track and this is indeed very special.
What I have found is 3 A1 synch mark at the beginning immediately followed by 3 huge NFA (all over 65ms)
So there not much to see ;)

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Re: Copy Protection details

Postby DrCoolZic » Sun Nov 13, 2011 6:33 pm

To be more precise 2 A1 + NFA + A1 + NFA

Code: Select all

KFAnalyze V1.1a (Nov  6 2011-18:32:47) - run Sun Nov 13 19:22:22 2011
  Stream file 'test010_stream00.0.raw' 5 rot - Avg RPM=300.68
  ** Border bits 22906 ns @ 22 ms Byte=0000 clk=4000
  ** MFM violation: Long spacing 22906 ns @22 ms Byte=0000 clk=4000
  ** Border bits 7385 ns @ 30 ms Byte=0000 clk=4000
  ++ $a1 Synch Byte  @62 Byte=0001
  ++ $a1 Synch Byte  @82 Byte=0002
  No Flux Transition Area 65594700 ns @65682 ms Byte=0003 clk=4000
  ++ $a1 Synch Byte  @65682 Byte=0003
  ** Invalid $00 byte (not an AM) after 3 Synch mark @65682
  ** MFM violation: Short spacing 2461 ns @65684 ms Byte=0005 clk=4063
  ** Border bits 3087 ns @ 65688 ms Byte=0005 clk=4063
  No Flux Transition Area 65600875 ns @131288 ms Byte=0005 clk=4031
  ** MFM violation: Short spacing 2503 ns @131291 ms Byte=07e7 clk=4031
  ** Border bits 3045 ns @ 131294 ms Byte=07e7 clk=4031
  ** MFM violation: Short spacing 3045 ns @131294 ms Byte=07e7 clk=4031
  No Flux Transition Area 65578469 ns @196872 ms Byte=07e7 clk=4000
  ** MFM violation: Short spacing 2461 ns @196875 ms Byte=0fd8 clk=4000
  ** Border bits 3087 ns @ 196878 ms Byte=0fd8 clk=4000

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Re: Copy Protection details

Postby mr.vince » Sun Nov 13, 2011 10:08 pm

I would have pressed the "like" button, but there wasn't any. ;)

Needless to say this is a real sample read from a real disk.

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Re: Copy Protection details

Postby ijor » Mon Nov 14, 2011 3:24 am

mr.vince wrote:Ok, coming back to this "strong DC erasure" thing.


I thought you said you didn't want to continue debating. I'm wondering why you changed your mind ... :)

Recording theory says you can't record this unless you use a permanent magnet.


I don't know where you got that theory. Not only that theory doesn't say that, but DC erase heads were (are?) actually used in some tape devices.

No signal would mean the drive turning up the "volume" (AGC) which should pick up random noise only.


Once again, I look at the protected track, and I see lot of things that are hard to explain. As I said, some of those protected tracks have lot of splices. There are major differences across different copies of the same title. And in some cases mayor differences across the tracks in the same disk. The area without transitions is not aligned. All these hints don't look as a simple "clean" flux transition pattern.

So what do you do to deliver proof? You build a "strong DC erasure" drive. This is what our friend Herzi over at a1k.org did. It's a modified floppy drive that has both heads replaced with two strong neodymium magnets. The electronics have a small circuit added that will monitor the disk insertion switch. As soon as it is activated, the motor will spin and step from 0 to 83 and back. Guess what... this erases the disk. :)


This doesn't really proof anything, except what you get with that specific device your friend built. Magnetic erasure is extremelly complex. There are many factors that affect the erasing. Of course that in your case, the disk spinning and the heads (or permanent magnets) stepping would produce a very strong effect, among other several factors.

And it is very unlikely that this really "degauss" (demagnetize) the disk. It might "erase" the old data (if there was any), but it probably won't leave the media demagnetized. As Dr.CoolZic is saying, your dump doesn't really look like a "virgin" track (or disk). I doubt this is just by chance.

High quality degaussers use a rather complex procedure, not only in terms of the applied magnetic field, but sometimes also the mechanical motion of the media.

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Re: Copy Protection details

Postby Dio » Mon Nov 14, 2011 9:14 am

Just need to heat the disk past the Curie temperature :) .

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Re: Copy Protection details

Postby DrCoolZic » Mon Nov 14, 2011 5:41 pm

WHAT Happen to the thread ??? We lost a lot of messages ???
Cant remember for sure but this was the thread with Turican ?
Did the moderator(s) removed information - can this be restored from backup ???
Last edited by DrCoolZic on Sun Nov 20, 2011 5:56 pm, edited 1 time in total.

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Re: Copy Protection details

Postby DrCoolZic » Mon Nov 14, 2011 5:42 pm

mr.vince wrote:Needless to say this is a real sample read from a real disk.

??? Waooo !!! what game ?
How would you check such a track with a WD1772 ?

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Re: Copy Protection details

Postby mr.vince » Sun Nov 27, 2011 3:34 pm

ijor wrote:I thought you said you didn't want to continue debating. I'm wondering why you changed your mind ... :)


I did not debate, I delivered facts.


mr.vince wrote:Recording theory says you can't record this unless you use a permanent magnet.

ijor wrote:I don't know where you got that theory. Not only that theory doesn't say that, but DC erase heads were (are?) actually used in some tape devices.


You are correct. And I corrected myself a couple of posts above. I have no problem doing that because it was nonsense (maybe my son nagged me, whatever). I am not going to correct myself twice.


ijor wrote:Once again, I look at the protected track, and I see lot of things that are hard to explain. As I said, some of those protected tracks have lot of splices. There are major differences across different copies of the same title. And in some cases mayor differences across the tracks in the same disk. The area without transitions is not aligned. All these hints don't look as a simple "clean" flux transition pattern.


We will be glad to help if you have any questions. Some things are impossible to see without the proper controller. Any title you are talking about int particular?


ijor wrote:High quality degaussers use a rather complex procedure, not only in terms of the applied magnetic field, but sometimes also the mechanical motion of the media.


Yeah, right. And these will create no-flux areas...?! How would that work?

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Re: Copy Protection details

Postby ijor » Mon Nov 28, 2011 5:02 am

DrCoolZic wrote:WHAT Happen to the thread ??? We lost a lot of messages ???


I splitted the thread. I created a new thread with the later messages about the "no flux transitions" issue. All the previous messages, with the generic copy protection stuff, are still present in the older thread. Nothing have been lost.

DrCoolZic wrote:
mr.vince wrote:Needless to say this is a real sample read from a real disk.

??? Waooo !!! what game ?


He said it is a real disk (meaning the dump wasn't artificially created, I guess). He didn't say it's an original disk.

mr.vince wrote:We will be glad to help if you have any questions. Some things are impossible to see without the proper controller. Any title you are talking about int particular?


It is not something specific to any particular title, it happens in just about any title with this protection. If you would examine the protected tracks carefully, you would probably understand what I'm talking about. I don't think the exact "controller" used would make much of a difference, as long as you use a flux transition level device, of course. Sometimes the particular copy makes a difference though, and the drive used for reading might make a difference as well.

ijor wrote:High quality degaussers use a rather complex procedure, not only in terms of the applied magnetic field, but sometimes also the mechanical motion of the media.

Yeah, right. And these will create no-flux areas...?!


Of course not, I didn't say anything like that. And I already said before that degaussed (demagnetized) media reads back as noise.

That sentence you quoted, was elaborating about the different types of magnetic erasures, and the complexity of the topic in general. And also in reply about what kind of erasing it would be expected from the device you described. I think the meaning of the sentence was quite obvious on the context of the post and its preceding paragraph.

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Re: Copy Protection details

Postby DrCoolZic » Mon Nov 28, 2011 10:48 am

ijor wrote:
DrCoolZic wrote:WHAT Happen to the thread ??? We lost a lot of messages ???


I splitted the thread. I created a new thread with the later messages about the "no flux transitions" issue. All the previous messages, with the generic copy protection stuff, are still present in the older thread. Nothing have been lost.

Not sure I understand why you did that ?
I finally found the original/first part of this thread viewtopic.php?f=47&t=19948

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Re: Copy Protection details

Postby ijor » Tue Nov 29, 2011 2:14 am

DrCoolZic wrote:Not sure I understand why you did that ?


Because the whole discussion about the no flux transitions was taking too long and was kinda "burying" the rest of the thread. I thought so it would better deserve its own thread. Like this we are better organized, we have this thread with its own subject, and the older one with the subject initiated by sarnau.

Isn't this the reason why we usually split topics, to better organize subjects and issues? I'm sorry if you didn't like it.

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Re: Copy Protection details

Postby DrCoolZic » Tue Nov 29, 2011 7:32 am

OK I understand but it that case you may want to rename this new thread as something as "no flux transition" and provide reference in both thread.
I think that having two different threads with the exact same title (I did not know this was possible in the same forum) is confusing and makes the "search" more difficult.

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Re: Copy Protection details

Postby ijor » Wed Nov 30, 2011 3:42 am

DrCoolZic wrote:OK I understand but it that case you may want to rename this new thread as something as "no flux transition" ...


Indeed, but the forum software (AFAIK) doesn't seem to allow renaming a thread. I found there is a partial workaround and just renamed (sort of) the thread title. But as you can see, the subject of the messages is not renamed :(

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Re: Copy Protection details

Postby mr.vince » Wed Nov 30, 2011 1:48 pm

ijor wrote:
mr.vince wrote:We will be glad to help if you have any questions. Some things are impossible to see without the proper controller. Any title you are talking about int particular?

It is not something specific to any particular title, it happens in just about any title with this protection. If you would examine the protected tracks carefully, you would probably understand what I'm talking about.


So what did we miss? We read it, analysed it, and even wrote it back to disk. If you are implying did not do it right, feel free to point your finger at me and let me (and the rest of interested people) know what we missed. Apparently it's not important, because as I said the chain is working, nevertheless it must be important and apparently beyond our capabilities. It feels a bit... odd.


ijor wrote:Of course not, I didn't say anything like that. And I already said before that degaussed (demagnetized) media reads back as noise.


So what is strong DC erasure being used for? It can't be for the "no flux" protection we discussed earlier.

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Re: Copy Protection details

Postby ijor » Fri Dec 02, 2011 7:45 am

mr.vince wrote:If you are implying did not do it right ... and apparently beyond our capabilities.


For the records. I didn't imply at all you did anything wrong, and I certainly didn't bring any such concept as something being beyond your capabilities.

So what did we miss? We read it, analysed it, and even wrote it back to disk...Apparently it's not important, because as I said the chain is working, nevertheless it must be important ... It feels a bit... odd.


In first place, it is not odd at all. Things are important or not depending on the purpose. A low level track dump has lot of information beyond what is strictly required for making a working copy. You know perfectly well that a "track" can tell (or at least hint) at being modified or not, (possibly) damaged, written with home or industrial equipment, or more generally, how it was duplicated, etc, etc. There are lot of details that are important (or at least useful or interesting) for this level of analysis, that are not so for writing back. And you surely know this.

To give another example, let's consider writing back weak bits. As you know, there are different type of weak bits. Some type of analysis can reveal the type of weak bits, which might be very interesting for the analysis. But in most cases this is not important for writing back. And you usually can write back weak bits with a different method than the one used originally at duplication.

Going back to what I meant. Look at the protected tracks and please tell me what you see. Do you see a regular constant pattern on the protection?

ijor wrote:Of course not, I didn't say anything like that. And I already said before that degaussed (demagnetized) media reads back as noise.

So what is strong DC erasure being used for? It can't be for the "no flux" protection we discussed earlier.


You are mixing erasure types once again. DC erasing (normally) doesn't demagnetize the media. If we use the degauss term in the strict sense (as demagnetize, and not just erase), then DC erasure doesn't degauss. Again, that's the reason that high quality degaussers use a complex (and usually both AC and with variable amplitude) procedure.


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