More about offsets?

[irishcrazy2005]

Originally Posted by 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?

So finally all those days I spent hanging around the EAC forums are paying off! Yes, you are correct that there is only an extraction error if it says "suspicious position..." or some other error message.

Here is the thing about Burst Mode: there is no error detection at all. It simply reads through the track as fast as it can and write the data to the file. This is why the track quality is always 100%, because the program never re-reads a sector, and thus according to the quote above, the track quality will be reported at 100%. It will not report any error messages unless ther is a serious problem and it can't read the disc at all. This is why we like secure mode .

-Phil

[Five]

thanks so much, I get it now.

one time I ripped twice and got 100.00% and 99.00% on two passes yet the checksums were the same. Now it all makes sense.

[feralicious]

Originally Posted by irishcrazy2005

...measure of the accurateness (I have no idea if that is actually a word or not, but I'm going with it)...

While accurateness got the point across, accuracy would've been more accurate.

[irishcrazy2005]

Originally Posted by feralicious

While accurateness got the point across, accuracy would've been more accurate.

Haha, thank you! Shows what kind of chemist I am......and to think that they're letting me get my PhD at Berkeley!

-Phil

[tgc225]

Originally Posted by irishcrazy2005

Haha, thank you! Shows what kind of chemist I am......and to think that they're letting me get my PhD at Berkeley!

-Phil

Interesting coincidence! My older brother is finishing his PhD at Berkeley in Chemistry (organic I think) this semester I'm not as smart as he is though Anyway, good luck with that program.

[feralicious]

Originally Posted by tgc225

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.

No, EAC will do what you tell it to do as far as the offsets. You have 3 choices, no offset, combined read/write offset which I believe should be used only when reading and writing with the same drive, and then a separate read and write offset which is what should be used when sharing, I believe.

What confuses me to this day is how to burn audio CDs with someone else's offset? I've looked for an answer a while ago and never found one. I believe you still use your drive's write offset since the read offsets are to correct whatever "inaccuracy" your drive does on audio cds due to not being able to easily locate sectors on audio cds.

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?

The Lead-In and Lead-Out are the parts of the disc before and after the written data. Some drives are able to read into these areas so that if your offset "pushes" some bits of data into one of them those drives can still read it and retrieve it, but those drives that cannot read into them will not be able to. It's been a long time since I configured my drive, but I believe EAC can determine whether or not your drive is able to read into them. If it cannot, I believe you should be sure to have it set to not do so as I think I read that it can harm your drive to set it to try to do it when it can't. Not sure about that part though.
More info: http://users.pandora.be/satcp/eacoffsets00.htm#-a



Another tip for anyone just configuring your drive. After you've spent 3-4 hours hunting through your CD collection to find CDs that match their database as the correct pressings for testing your drive's offsets, make a note on which CDs they were. I can't remember which ones worked for me and I have a feeling that the drive I have all configured is on its last legs. Which means I have to go throught the whole process all over again when I buy a new drive. Wish I knew which CDs those were....

Oh, and also write down your read, write and combined offset numbers with the CD names in case you have a bad computer day and you lose your C drive.

[tgc225]

Thanks for the info. I think the most reasonable explanation when it comes to incorrect offsets is that someone bought a new drive but didn't bother to change the offset value. For a few boots that I checked, while the offset value didn't match the drive that was in the log, it did match other drives in the database.

[feralicious]

Originally Posted by irishcrazy2005

Haha, thank you! Shows what kind of chemist I am......and to think that they're letting me get my PhD at Berkeley!

-Phil

At least it's not in Linguistics.

[Five]

Originally Posted by feralicious

What confuses me to this day is how to burn audio CDs with someone else's offset? I've looked for an answer a while ago and never found one. I believe you still use your drive's write offset since the read offsets are to correct whatever "inaccuracy" your drive does on audio cds due to not being able to easily locate sectors on audio cds.

As I understand it, with separate read and write offsets this means that any cd ripped with EAC with the read offsets corrected can be written as an exact audio copy on any drive with the write offsets corrected (for that specific drive). If you have a drive that forces you to use a combined read/write offset it is not possible to make exact audio copies unless you do it on your computer only. I think this ties in the the Lead-In and Lead-Out stuff.

Originally Posted by feralicious

Another tip for anyone just configuring your drive. After you've spent 3-4 hours hunting through your CD collection to find CDs that match their database as the correct pressings for testing your drive's offsets, make a note on which CDs they were. I can't remember which ones worked for me and I have a feeling that the drive I have all configured is on its last legs. Which means I have to go throught the whole process all over again when I buy a new drive. Wish I knew which CDs those were....

I remember what worked on mine... Led Zeppelin BBC Sessions! You're supposed to test with more than one disc, so this one works great since it's a 2cd set. I should probably also mention that mine is the Canadian pressing. Also a great listen fwiw.

Originally Posted by feralicious

Oh, and also write down your read, write and combined offset numbers with the CD names in case you have a bad computer day and you lose your C drive.

Now this is some good advice! *gets pencil and paper out*

Originally Posted by tgc225

Thanks for the info. I think the most reasonable explanation when it comes to incorrect offsets is that someone bought a new drive but didn't bother to change the offset value. For a few boots that I checked, while the offset value didn't match the drive that was in the log, it did match other drives in the database.

This theory makes sense. It seems like a pretty obvious mistake to avoid, but I could see this happening to ppl who configured EAC a couple years back and have since forgotten everything except "I did it".

Originally Posted by Five

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.

Tedious is a polite way of wording it.

Originally Posted by Five

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

Some drives can read into the 'leadin', some can read into the 'leadout', some can do both, (most) can do neither. This is also called 'over reading'.

The leadin and leadout are parts of the audio CD required by the redbook standard and placed at the very beginning and very end of the audio respectively, as the names imply. When you rip a disk with correct offsets, your drive doesn't actually read into the leadin or leadout but it thinks it is doing one or the other because it has been told to apply an offset. For instance, if your read offset correction is +98 this tells your drive to start reading 98 samples ahead of usual. The drive therefore thinks that when it gets to the end of the disk it has to read 98 samples into the leadout before stopping. It's not really reading into the leadout but it thinks it is, so if the drive can't read into the leadout it won't be able to read those last 98 samples. If your drive can't read into the leadout set EAC to 'fill missing samples with silence'. Odds are that those missing 98 samples were silence anyway.

You can tell if your drive reads into the leadin or leadout from the tables, or you can tell by adjusting the offset and seeing if you get sync errors. If you have a positive offset correction and always get a sync error on the last track when you tell EAC to over read then your drive can't actually read into the leadout. Likewise if you have a negative offset correction and your drive can't read into the leadin, you will get sync errors on the first track if you tell EAC to over read. Note that there is only one setting for reading into both the leadin and leadout in EAC. So here's a summary:

- positive offset correction - drive must read into leadout - if it can't, turn off over reading and set to 'fill in missing samples with silence'

- negative offset correction - drive must read into leadin - if it can't, turn off over reading and set to 'fill in missing samples with silence'

Strictly speaking exact copies are NOT possible if the extracting drive cannot over read as required. This is most drives. Oh well.

Originally Posted by Five

I would rather if ppl took the time to actually test the real offset values for their specific drives.

This is only possible by looking up the values in the published tables or by using a proper EAC configuration disk, i.e. a disc published in the tables or one made on a computer with proper write offset. (There is a third way to determine your read offset using ADD or AAD CDs, but it is so incredibly complicated that I would recommend it to no one.)

Originally Posted by Five

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.

This is indeed rare and shouldn't happen with newer drives, i.e. anything more than 3 years old.

Originally Posted by Five

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.

I agree. If you don't know what your read offset correction is, don't guess. Set it to ZERO.

Originally Posted by Five

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.

Write offset only matters for burning CDs, and combined offset is only for copying CDs when you don't know your read or write offsets (because you can calculate your combined offset from any CD).

From TTD's perspective all that matters is that the person who ripped a CD for torrenting here used the correct read offset (or used no read offset correction at all). NEVER use combined offset for ripping and torrenting files.

Provided the files were ripped with proper offsets you never have to worry about another person's offsets when you burn the files to CD on your own computer. In fact, you NEVER have to worry about that even if they used the wrong offsets. If they used the wrong offsets and actually lost audio samples, you can't get them back anyway. The only thing you need to be concerned about is if you notice that there is no silence at all at the beginning of the first track or the end of the last track. You could end up losing some of the audio if you burn without write offset correction or can't write into the leadin/leadout. And remember, you want a CD that can play in any CD player out there, and NONE of them use offset correction during playback. But there is a very simple solution: just add a second of pure digital silence to the very beginning and very end of the disc before burning. Even half a second will be more than sufficient since that equals 22,050 samples, which is way way more than any read or write offset that I have ever seen. But I always add one second if necessary since that entirely avoids creating an SBE issue. (Whatever amount you add, just make sure it's an integer multiple of 588.)

Originally Posted by Five

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?

No. Burst mode doesn't apply any error checking so all that 'copy ok' means in burst mode is that EAC was able to read the whole track, but with no guarantee of accuracy. You should only use burst mode on a really bad disk that just can't be read in secure mode or paranoide mode, in which case you should use 'test & copy'. If you get the same CRC for the test read and the copy read then you're getting as high quality as you can possibly get from burst mode.

[tgc225]

Originally Posted by uhclem

From TTD's perspective all that matters is that the person who ripped a CD for torrenting here used the correct read offset (or used no read offset correction at all). NEVER use combined offset for ripping and torrenting files.

So can the offset stuff I mentioned in post #14 be added to to FAQ I really like the website for enforcing high standard already, and since most people here are already keen about using silver discs and EAC secure mode, making sure read offsets are set correctly shouldn't be much of a problem.

And sorry for all the complaining and not much contributing yet, but I'm still waiting on PNY for my replacement video card that's on my main computer

[Five]

we're waiting for our "Renegade Geek" to step away from World Of Warcraft and approve this

Originally Posted by tgc225

And sorry for all the complaining and not much contributing yet, but I'm still waiting on PNY for my replacement video card that's on my main computer

No sweat, seed when you find the time. You've helped me out tremendously with your posts & seeds across several sites now. It's always great seeing a fellow Beatlemaiac around these parts.

Speaking of which, where's your cool avatar?

[tgc225]

I have one more question that I wanted to clear up. I was reading the Coaster Factory link, and I'm a little confused. As far as I understand, to burn a new disc that will match an original, you need:

1) Someone to rip with EAC with the correct read offset
2) Then you need to burn using EAC with the correct write offset (and you can only use EAC to burn, because it's the only program that supports seperate write offsets)

Or, the person who rips can rip with combined read/write offsets, and when you burn the file to a disc, it'll be correct, but the files on the hard drive have incorrect offsets.

Is this correct?

EDIT: I did a little bit of reading, and looks like I was wrong about the second option. If combined offets are used, then the burn must be made on the same drive from which it was ripped.

[Five]

that's right, including the edit... except the combined read/write offsets might be for two drives, your rom drive and your burner would be usual. don't use this option unless you have to!

the best thing to do is test if you can do an exact audio copy using your own computer and separate read and write offsets.

I did this. I set up all my offsets, ripped a silver cd, then I generated a wholefile .md5 for the WAVs. I burned an audio cdr from these WAVs, switched it to the read drive, then ripped this cdr to a new folder. I tested the .md5 I created from the silver rip and it was perfect. EAC also mistook my audio cdr copy for the original silver when I put it in.

The only thing left to test would be to rip a cdr on another computer then follow thru the steps and see if the .md5 still works. I'm pretty sure it will.