More about offsets?

[tgc225]

From what I understand, the absolute most accurate way to rip a CD is with sample offset correction, because if offsets are used, two people can rip the same CD on different drives and get exactly matching file.

Anyway, so how about requiring people to write whether they used offset correct or not when ripping the disc? This should be simple, because all people have to do is write "no offsets corrected" or "offsets corrected" and that will be it. Lots of people just write "EAC (Secure)", but this terminology is unlcear when it comes to whether offsets were used or not.

Also, maybe there could be a little guide on this website (or some links pointing to other guides) that explain and encourage the use of offsets when ripping? This website, for example, has a database for offsets for many drives, so that will eliminate the need to burn sample discs to figure out what your drive offset is:

http://accuraterip.com/driveoffsets.htm

[Five]

This is a good point... I've got the link in my signature to the coaster factory which describes all of this in great detail including why it's important and how to configure EAC properly.

It would be great if ppl posted whether their offsets are corrected, but first priority even before that would be to get ppl to generate an EAC .log and include it with the show. From this log it can be seen whether the offsets have been corrected and other critical data can be reviewed such as track quality. It's great if a CD/CDR is ripped with EAC with the offsets corrected but if the track quality is 67.00% on several tracks then the .log file is the thing that matters much more. Two silvers from the same pressing run can be extracted on two computers with offsets corrected and come up with the same .st5 / .ffp checksum values, but only if the quality is 100.00% (or perhaps very very close) on all tracks.

[tgc225]

Ah, thanks about mentioning that EAC logs had the offsets, I didn't know that.

Anyway, I checked all of my old bootlegs, and I've found a lot of variation. Some had '0' as the offset value, while many others had incorrect values (I found the name of the drive in the log file, and then checked the AccurateRip database for that drive, and many boots had an offset value that didn't agree with the value in the database. For many of these drives, the AccurateRip database had many submitters confirm the correct value, so the person who ripped the disc must have had it wrong). Maybe EAC tries to guess a value in some cases? Also, there were a number of boots whose value did match the AccurateRip database, I guess those are the most accurate. Also, a number had "Overread into Lead-In and Lead-Out : Yes", while most had "No". What's the difference between that?

Anyway, I think maybe that AccurateRip database link should possibly be stickied somewhere or linked in the FAQ. I think some newbies are reluctant to start off with EAC because of the need to configure it, and the offset part was a little lengthy and confusing. With the AccurateRip database, it's as simple as copying and pasting the number and that's it, so maybe more people will take advantage of that feature.

And maybe we could get some of the more advanced users contribute to the database to save time for newbies

[Five]

99% of the time, if 0 is the offset value, EAC wasn't set that way. I saw one guy posting that his drive truely has an offset of zero samples, but that's a pretty damn rare case.

For my drive that I could find listed the numbers were accurate compared to what I got by doing all the coaster factory stuff. I used a cd from their list (Zeppelin's BBC Sessions) and ran it several times on both cds to test it. Came up with +98. Some of my earlier seeds you can see in my .log files that my offset was not adjusted (i.e. 0), but you can also see that the extraction quality is 100.00%. Somebody really tedious could look up my drive and shift everything over by exactly 98 samples then the files would theoretically be exactly the same as an offset-adjusted rip. When I've got some time on my hands I'll play around with this. Knowing that the files are otherwise identical by checking extraction quality in the .log this is a nice detail to watch but not exactly the end of the world (don't quote me on that!).

I believe the coaster factory is linked by RainDawg all over the FAQ, check it out.

Originally Posted by tgc225

Also, a number had "Overread into Lead-In and Lead-Out : Yes", while most had "No". What's the difference between that?

I'll have to look that up... does anybody know this offhand?

Originally Posted by tgc225

Anyway, I think maybe that AccurateRip database link should possibly be stickied somewhere or linked in the FAQ. I think some newbies are reluctant to start off with EAC because of the need to configure it, and the offset part was a little lengthy and confusing. With the AccurateRip database, it's as simple as copying and pasting the number and that's it, so maybe more people will take advantage of that feature.

I would rather if ppl took the time to actually test the real offset values for their specific drives. There is possibility for variation even with the same model drive so the only truely accurate way to configure EAC is to do those tedious tests. Even then, some drives will have different offsets at different times of the day! In this case, an average has to be taken by the user and manually entered. Thankfully, this is a rare occurance. If ppl are lazy and just punching in a number it's implied by the .log that they have actually tested their drive several times to arrive at that number. If that's not the case I would rather just see a zero. I'm not sure if everybody would agree with me on this.

Then there are some cases where the coaster factory says your configuration necessitates using the undesirable comined read/write offset which means true exact audio copies would only be possible on the computer the cd was ripped on. So at this point we are demanding EAC and strongly (and I mean strongly!) recommending you visit the coaster factory and take a couple hours to set your offsets properly, which is not possible for 100% of the drives out there. Still, ripping with EAC is always better because of the error reports and strong probability that you can get your offsets perfect if you just take the time to do the tests.

If advanced users want to write tutorials they will be welcomed with open arms! There's not enough hours in a day to write all of the guides we want for the site, so if anybody so inclined is reading this, go for it! Unless the technobabble mods (and technobabble postwhores) find misinformation we will use it.

[tgc225]

Alright, thanks for all the info

Anyway, I think the AccurateRip database might be pretty accurate. It says that "A small number of drives have [Purged] as the offset, these drives were found not to have a constant drive offset (perhaps different manufacturing batches, or firmwares), as such they have been removed from AccurateRip's drive database".

I'm not sure exactly how the database works yet, but I believe when you rip one of the key discs they have in the disc database, and your files exactly match someone elses rip, you get added to the offset database. Since drives with different offsets are purged, the drives that do have many submitters with the same offset is probably very accurate at that point.

Anyway, there's so much of this technical stuff with CDs Good thing a straight file format was used with DVDs

[Five]

nothing is perfect, is it?

I just saw another thread up in technobabble saying that trading audio is more secure than trading DVDs at this point!

It sounds like the AccurateRip database is pretty good... makes me wonder where some of those ppl are getting their offset values you read in the .log files.

[Five]

come to think of it, I'm gonna move this to technobabble where we might get more responses. I can always move it back later if you want.

[irishcrazy2005]

Originally Posted by Five

It's great if a CD/CDR is ripped with EAC with the offsets corrected but if the track quality is 67.00% on several tracks then the .log file is the thing that matters much more. Two silvers from the same pressing run can be extracted on two computers with offsets corrected and come up with the same .st5 / .ffp checksum values, but only if the quality is 100.00% (or perhaps very very close) on all tracks.

I could be wrong here, but from I understand the track quality percentage is not actually a measure of the accurateness (I have no idea if that is actually a word or not, but I'm going with it) of the extracted track. I believe that it is actually a representation of the physical quality of that track on the disc (it is a measure of how many rereads EAC must do to get an exact copy). As long as there are no errors reported on the track, it is an exact copy of the track. I forget where I read this, but it was either at the Coaster Factory or at the EAC forums. This explains why you can rip a brand new CD that you just took out of the wrapper and note get 100% on all tracks.

-Phil

[Five]

I've never read that... I've had discs where I had to rip several times and switch from secure to paranoid mode to get 100.00% quality. This would imply to me that the track quality is the quality of the rip since I was using the same cd. I've also read other ppl saying that they had to rip several times to get 100.00%...

[irishcrazy2005]

Originally Posted by Five

I've never read that... I've had discs where I had to rip several times and switch from secure to paranoid mode to get 100.00% quality. This would imply to me that the track quality is the quality of the rip since I was using the same cd. I've also read other ppl saying that they had to rip several times to get 100.00%...

Right, what I am saying is that you don't need it to say 100% to be a completely accurate rip. As long as each track says "Copy OK" and the bottom says "No errors occured," then the disc was copied exactly. I am going to dig through and try to find where I read this now.

-Phil

Edit: Okay, here it is. It's from The Coaster Factory:

While Peak level tells nothing about the quality of extraction, Track quality does. A Track quality of 100% obviously means that the track was extracted 100% correct. But here's where some people make mistakes; sometimes EAC rereads certain audio sectors multiple times to get accurate extraction results. For every reread EAC does, the Track quality decreases, but this does not mean that the extraction is less accurate. It is possible to have a bit-by-bit perfect copy of a track, while Track quality is lower than 100%. As long as Exact Audio Copy does not report any errors in the Status and Error Messages log, the extracted files are bit-by-bit perfect copies of the original. Track quality should be interpreted as the physical quality of the CD and not of the extracted data. A CD with some scratches or dirty fingers on will certainly cause rereads in EAC and thus a Track quality lower than 100%, but still the extracted tracks may be perfect. Thus if the log says Copy OK for a track that means it's extracted perfect - no matter of the Track quality. So, I hope that made things more clear as many people are confused by the Track quality.

Here is the exact link if you wish to read more http://users.pandora.be/satcp/eac07.htm#-

[tgc225]

I think this is the relevant section:

http://users.pandora.be/satcp/eac07.htm

While Peak level tells nothing about the quality of extraction, Track quality does. A Track quality of 100% obviously means that the track was extracted 100% correct. But here's where some people make mistakes; sometimes EAC rereads certain audio sectors multiple times to get accurate extraction results. For every reread EAC does, the Track quality decreases, but this does not mean that the extraction is less accurate. It is possible to have a bit-by-bit perfect copy of a track, while Track quality is lower than 100%. As long as Exact Audio Copy does not report any errors in the Status and Error Messages log, the extracted files are bit-by-bit perfect copies of the original. Track quality should be interpreted as the physical quality of the CD and not of the extracted data. A CD with some scratches or dirty fingers on will certainly cause rereads in EAC and thus a Track quality lower than 100%, but still the extracted tracks may be perfect. Thus if the log says Copy OK for a track that means it's extracted perfect - no matter of the Track quality. So, I hope that made things more clear as many people are confused by the Track quality.

[irishcrazy2005]

Ah, I beat you to it by just a few seconds!!!

-Phil

[Five]

ahh, I see!

you learn something every day.

so there's only extraction errors when it says something like "suspicious position at..." or if it doesn't say "copy ok". but when you use burst mode, it says "copy ok" too does that mean that burst mode is also 100% accurate?

[tgc225]

Now that's a good question. Unfortunatly, it looks like The Coaster Factory doesn't go into describing burst mode at all, only reccomending that secure mode is used (which is what many other websites do). Maybe there's a comparison out there ripping a poor quality disc in both mods and seeing if the files are the same for either mode, but I haven't found such a site yet.

Anyway, back to offsets and track quality, that note seems to suggest that as long as offsets are configured correctly, and there are no errors during the extraction process, theoretically everything should match up. In any case, I don't think it would hurt to add the AccurateRip DB link to #6 of the Audio BitTorrent Seeding Policy, along with the "offsets" thing in the #8 lineage section (since many people do it already), though that's completely up the moderators whether that info is helpful or not.

[Five]

that sounds like a great idea to me, I'll pass it along.