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Why can't you extract all the data on a factory-pressed CD when it
guest0190
post Sep 5 2012, 21:28
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In the past when I have burned a CD with EAC (with read and write offset correction values consistent with Andre Wiethoff's reference), I have been able to rip files from it identical to the source files.

Based on what I could gather from this forum, I used to be of the conviction that with a drive capable of overreading and overwriting, the exact same files that were burned to a CD can be extracted from it again, and that the only disadvantage of using a drive not capable of overreading was that a few samples at the beginning or end of the first or last audio file would be replaced with silence, regardless of what the samples originally contained.

Recently, however, it has come to my understanding that it is very hard (or even impossible) to extract the original files that were burned to it from a mass-produced CD.

My question is simple: How is it that I can rip files identical to the source files from a CD I have burned myself, but not from one that is factory-pressed? And, perhaps more importantly, how is it that I managed to achieve this using 'incorrect' offset values?

I apologise in advance for any difficulty I might have understanding any mathematical arguments you put forth. I fear I am slightly dyscalculic.

(I have decided, henceforth, to rip using the 'ideal scenario' reference which is 30 samples before that established by Mr Wiethoff, but I am not sure if it is relevant.)
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guest0190
post Sep 6 2012, 20:22
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http://www.digital-inn.de/exact-audio-copy...se-offsets.html
http://www.digital-inn.de/exact-audio-copy...ay-offsets.html
http://www.hydrogenaudio.org/forums/index....showtopic=50301
http://club.myce.com/f61/offsets-handling-...channel-111913/

There are a few links relevant to the topic. I am not sure if any of them explicitly states that the differences between these two references (which I will readily admit I do not understand in the first place) prevents extraction of the same files that were burned to the CD, but that was how I interpreted it.

The bottom line, as far as I can tell, seems to be that it is hard to tell where the actual data on the CD starts. (I have previously shared with greynol that this strikes me as unintuitive, as I feel that the CD drive should have no problem recognising where the little pits on the surface of the disc start and where they end - but that is an aside.)

Again, my problem is that I have a hard time understanding how this is consistent with the fact that my own experiments showed me that I could indeed get the same files back from a CD that I burned to it.

Another, albeit related, thing that confuses me, is how I were able to accomplish this despite my drive consistently reading 30 samples prior to where it 'should' be reading. I suspect the answer lies in basic math, but nonetheless, I would be glad if someone could clarify.
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db1989
post Sep 6 2012, 21:24
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QUOTE (guest0190 @ Sep 6 2012, 20:22) *
There are a few links relevant to the topic. I am not sure if any of them explicitly states that the differences between these two references (which I will readily admit I do not understand in the first place) […]
IpseDixit’s later calculated reference is verifiable as being exactly correct, meaning that a drive calibrated to it will not exhibit any offset between the times of the data that are requested and the data that are actually returned. Andre’s is a bit off (30 samples, to be exact), but most applications supporting offsets and verification of tracks according to them (read: about three) were firmly entrenched in using it by the time IpseDixit presented his findings, so they tend to offer the new offset as an optional extra if at all.

QUOTE
[…] prevents extraction of the same files that were burned to the CD, but that was how I interpreted it. […] Again, my problem is that I have a hard time understanding how this is consistent with the fact that my own experiments showed me that I could indeed get the same files back from a CD that I burned to it.
No one has said anything about not being able to extract the same audio, but you must account for offsets to ensure that you don’t miss a bit at the start or end, by accounting for the offsets of both the present reading drive and the and antecedent writing drive.

QUOTE
The bottom line, as far as I can tell, seems to be that it is hard to tell where the actual data on the CD starts. (I have previously shared with greynol that this strikes me as unintuitive, as I feel that the CD drive should have no problem recognising where the little pits on the surface of the disc start and where they end - but that is an aside.)
It’s quite simple. The audio is written as a continuous stream in the main data, whereas the information on which parts of it correspond to which tracks is written elsewhere. Your drive can get information on what to read, either from the table of contents or from your instruction, but it’s not necessarily true that it can then seek to exactly the right place in the nondescript stream of audio.

QUOTE
Again, my problem is that I have a hard time understanding how this is consistent with the fact that my own experiments showed me that I could indeed get the same files back from a CD that I burned to it.
Again, no one has said that this is impossible, so please do not portray anyone as having done so. It’s perfectly possible, just maybe with a little preparation.

QUOTE
Another, albeit related, thing that confuses me, is how I were able to accomplish this despite my drive consistently reading 30 samples prior to where it 'should' be reading. I suspect the answer lies in basic math, but nonetheless, I would be glad if someone could clarify.
Did you apply offset correction during reading and writing, or if not does your drive have inverse read (e.g. +30) and write (e.g. -30) offsets? Again, this isn’t very complex.

This post has been edited by db1989: Sep 6 2012, 21:26
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Posts in this topic
- guest0190   Why can't you extract all the data on a factory-pressed CD when it   Sep 5 2012, 21:28
- - AndyH-ha   Do the offsets have anything to so with anything e...   Sep 5 2012, 22:19
- - pisymbol   Is this the TAO (track at once) vs DAO/SAO (disc a...   Sep 5 2012, 22:59
- - 2Bdecided   There's subcode, HTOA, offsets, pregaps etc wh...   Sep 6 2012, 10:31
- - Rollin   If your drive has positive offset correction value...   Sep 6 2012, 14:09
|- - pisymbol   QUOTE (Rollin @ Sep 6 2012, 09:09) If you...   Sep 6 2012, 16:49
- - greynol   You need to take into account the offset of the bu...   Sep 6 2012, 15:11
- - greynol   Countless discussions on this forum, digital-inn, ...   Sep 6 2012, 17:31
|- - pisymbol   QUOTE (greynol @ Sep 6 2012, 12:31) Count...   Sep 6 2012, 20:15
- - Manlord   QUOTE (Rollin @ Sep 6 2012, 15:09) If you...   Sep 6 2012, 18:30
- - greynol   The greatest number of samples that can be replica...   Sep 6 2012, 18:55
- - guest0190   http://www.digital-inn.de/exact-audio-copy...se-of...   Sep 6 2012, 20:22
|- - db1989   QUOTE (guest0190 @ Sep 6 2012, 20:22) The...   Sep 6 2012, 21:24
- - greynol   Didn't we just have another discussion saying ...   Sep 7 2012, 01:51
- - hyman   QUOTE (greynol @ Sep 7 2012, 00:51) Didn...   Sep 7 2012, 08:12
|- - greynol   QUOTE (hyman @ Sep 7 2012, 00:12) From my...   Sep 7 2012, 12:30
- - guest0190   Thank you all for your answers. So if I understan...   Sep 7 2012, 16:15
|- - Porcus   QUOTE (guest0190 @ Sep 7 2012, 17:15) in ...   Sep 7 2012, 19:35
- - Manlord   QUOTE (guest0190 @ Sep 7 2012, 17:15) My ...   Sep 7 2012, 17:05
- - greynol   You won't be able to use CT to check titles ri...   Sep 7 2012, 17:10
- - guest0190   QUOTE You won't be able to use CT to check tit...   Sep 7 2012, 22:47
- - korth   Lack of programming to do cross-pressing verificat...   Sep 7 2012, 23:05


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