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Drive offset and its affect on last sector during CD rip
post Dec 7 2012, 04:41
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Hello. As per the title I have a few questions regarding drive offset and its affect with ‘last sector’ handling during CD ripping.

Some years back I ripped my CD collection using EAC to single image (album) FLAC with cuesheet. Not sure why but a week or so back I decide to have a look at CueRipper and grabbed a random CD (Pink Floyd – The Final Cut). I actually hit an issue with CueRipper with it raising an exception during gap detection (as per another thread) but that’s not the reason for the post.

What I discovered was that the MD5 within the FLAC was different to my earlier ripped master. My initial reaction was along the lines of what the...

As it happens I have 2 notebooks and 2 PC. The PC that was used for the ripping was retired but I managed to resurrect it and repeat the rip and it got the same MD5 as what was in the original (so the same system got the same MD5).

I then tried all others systems and found a relationship between the offset. Somewhat by chance, two systems have an identical offset of +102 and two have an identical offset of +667. Each system with the same offset results in the same MD5. In all cases, AccurateRip results (both AR1 and AR2) following ripping are fine.

Next step was to compare WAV files so I decoded each of the FLAC and compared within EAC. Both files are bit identical right up to what I would call last sector with the variation occurring in last 0.013’ of the WAV file (so last 1/75).

Upon reflection I expect this is probably quite normal and I note that AccurateRip does not use last 5 sectors (2940 samples) for its calculation. I presume this is intentional due to drive variation and the like.

I guess the question is should I be concerned about this or is this a case of OCD getting the better? Is there any ripping means that overcomes the variation of offset and drive capability that will result in bit identical WAV? Keep in mind I’m asking about the very last samples; I expect everything up to then to be bit identical which is the purpose of the offset value used with ripping.

It does seem to me that consistency will only be achieved where the drive has an absolute offset of less than or equal to 588. Any offset larger than that will result in a variation subject to EAC settings, offset value and drive capability when ripping the last samples.

Just out of curiosity, the FLAC MD5 for the album as above comes out as per below. I’d be interested in the value that others have for comparison as it will confirm my thinking to the cause and maybe as to which is the ‘better’ image copy. Thoughts?

Offset +102 FLAC MD5 9f9bbafb2937a6466c6ca54ab472b598
Offset +667 FLAC MD5 1111c22a05506dc693b57dc83cca727e
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post Dec 12 2012, 01:24
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Actually I would have to expand on what I said 4 years ago, if a drive cannot overread and the ripper fills those missing samples with zeros (and they are zeros on the disc) then you would get a consistent CRC, but not for the case where there are samples right to the end (typically it could be background silence, or a badly mastered disc where the audio cuts out short).

The issue here are rippers which try to read TOC end - X, where X happens to be number that the ripper is using (ie track len / reading LBA block size), the failure to read will not only be a failure of the last sector, but the whole lot, potentially 30 sectors which is then silenced by the ripper. dBpoweramp will on a failed read of last sectors, scale back the request so it falls back within the LBA range and zero the missing part.

I would have to actually say, for most people testing such is difficult, because you would have to have a CD which is audio to the end, or make one. Also different drives do different things, I am sure I have seen a drive which was happy to pretend to overread, as long as there were silence beyond the end, but as soon as there is real audio it failed...

This post has been edited by spoon: Dec 12 2012, 01:28

Spoon http://www.dbpoweramp.com
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post Dec 12 2012, 02:12
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Thanks Spoon. And I used dBPA and compared to EAC regardless of setting I get a consistent rip with matching MD5 and checksum for AR. So chalk one up for dBPA I guess. To be clear, the very last sample are different betwen the systems with +102 and +667 offset but I understand the reason now. Cheers.
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Posts in this topic
- kudabird   Drive offset and its affect on last sector during CD rip   Dec 7 2012, 04:41
- - Cynic   I think this has to do with overreading, since bot...   Dec 7 2012, 15:49
- - psycho   kudabird, your MD5 hashs tell us nothing, if you d...   Dec 7 2012, 17:31
|- - kudabird   QUOTE (psycho @ Dec 8 2012, 02:31) kudabi...   Dec 8 2012, 22:55
- - greynol   QUOTE (kudabird @ Dec 6 2012, 19:41) Is t...   Dec 9 2012, 16:35
|- - kudabird   QUOTE (greynol @ Dec 10 2012, 01:35) QUOT...   Dec 10 2012, 01:27
|- - greynol   QUOTE (kudabird @ Dec 9 2012, 16:27) A se...   Dec 10 2012, 05:38
- - kudabird   It with some trepidation that I post again but wha...   Dec 10 2012, 11:17
|- - greynol   While I can lead you to water... QUOTE (kudabird ...   Dec 10 2012, 16:31
- - kudabird   Hello. I actually started a reply but deleted my d...   Dec 11 2012, 23:21
|- - greynol   QUOTE (kudabird @ Dec 11 2012, 14:21) I f...   Dec 12 2012, 02:08
- - spoon   Actually I would have to expand on what I said 4 y...   Dec 12 2012, 01:24
|- - kudabird   Thanks Spoon. And I used dBPA and compared to EAC ...   Dec 12 2012, 02:12
|- - kudabird   I was all set to concede the use of LBA was mispla...   Dec 12 2012, 02:49
- - greynol   Again, there is no LBA in Red Book. To use the te...   Dec 12 2012, 02:56
|- - kudabird   QUOTE (greynol @ Dec 12 2012, 11:56) So c...   Dec 12 2012, 04:01
- - greynol   LOL. Well I do have egg on my face and humbly adm...   Dec 12 2012, 04:10
|- - kudabird   All good. And I've got to say I too had a bit ...   Dec 12 2012, 04:23
- - spoon   There is nothing wrong with using the Term LBA and...   Dec 12 2012, 12:08
- - greynol   Again(!) Red Book makes no mention of LBA. CD...   Dec 12 2012, 17:15
|- - hyman   Elaborating from Spoon to make it more clear for o...   Dec 12 2012, 17:36
|- - greynol   QUOTE (hyman @ Dec 12 2012, 08:36) it see...   Dec 12 2012, 21:53
- - spoon   I thought this thread was about cd ripping...not a...   Dec 12 2012, 21:42

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