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Why can't you extract all the data on a factory-pressed CD when it
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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post Sep 7 2012, 08:12
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QUOTE (greynol @ Sep 7 2012, 00:51) *
Didn't we just have another discussion saying fairly clearly that pits and lands do not directly translate to bits in the audio stream and that the data for each frame of audio is distributed over an area so errors can be corrected perfectly from minor damage?

It shouldn't be too much of a stretch to accept that such a scheme would result in different hardware resolving the data to any specific address differently; especially when the specification does not require address resolution to an exact sample.

Combine this with pressings that differ by thousands, if not tens of thousands of samples (or more!) on a track by track basis and you quickly realize that this reference business is much ado about nothing.

That is not quite correct. The spreading is part of the encoder called CIRC scheme (consisting of delays and interleaves stages) and it is fixed, i.e. same spread amount is applied to all samples/sectors. The problem arises because the specification:
1. is to have the subchannel which contains the addressing (location) data to be treated as a separate stream from the audio samples data (main channel) (as mentioned by db1989)
2. does not describe that subchannel should be perfectly aligned from subchannel address 00:00.00 to first audio sample, so hardware designers found it easier to simply leave the skew (offset) created by the buffering used for the "spreading" of bytes (CIRC).

From my understanding it appears you are implying a randomness? Not quite, the offsets were a result of the buffering skew and are fixed values for each drive, in contrast the CIRC "spread" is the same for all drives. The randomness is when observing among different drives (ones using different buffering skew).

Pressed CD have recorded offsets because this applies to pressing plant recorders (LBR) as well, simply because they are glorified (made of higher quality) CD writers, many of which the chipset is from ordinary consumer manufacturers (e.g. TEAC, Sony) so these LBRs will naturally have a write offset, and further complications arise because if every plant use a different LBR they will be recording with a different write offset to the CD glass master.

This post has been edited by hyman: Sep 7 2012, 08:14
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post Sep 7 2012, 12:30
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QUOTE (hyman @ Sep 7 2012, 00:12) *
From my understanding it appears you are implying a randomness?

Not at all, no. While I wasn't specific about the mechanism (which was already given in the cdfreaks discussion that the OP read), I did say the spec does not impose the requirement that there be sample-accurate indexing. Rather, I was simply trying to point out that the pits and lands are not laid out in the same sequential way that analog audio is laid out on tape or vinyl.

This post has been edited by greynol: Sep 7 2012, 12:35

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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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