Andre's EAC Offset Calculation Options

[Moitah]

For what it's worth, I used a method similar to the one described on Pio2001's page. I did it on 74 CDs, the results are here:

CODE

2Gether-2Gether 15622 -4507
2Gether-Again 15319 -20753
98_Degrees-98_Degrees_And_Rising 14477 -29145
98_Degrees-Revelation 16172 -7003
98_Degrees-This_Christmas 15337 -108250
Aly_And_AJ-Acoustic_Hearts_Of_Winter 14760 472
Aly_And_AJ-Into_The_Rush -1160 -12
Aly_And_AJ-Into_The_Rush_(Deluxe_Edition) 318 472
Aly_And_AJ-Into_The_Rush_(Japan) 147 -789
Aly_And_AJ-Into_The_Rush_(Rerelease) -1160 -13
A-Teens-Teen_Spirit 15674 -23659
A-Teens-The_ABBA_Generation 16968 -5169
Avril_Lavigne-Let_Go 15360 -13854
Backstreet_Boys-Backstreet_Boys 16551 -12
Backstreet_Boys-Black_And_Blue 23348 -11448
Backstreet_Boys-Millennium 17101 -5585
BBMak-Into_Your_Head 17921 -36561
BBMak-Sooner_Or_Later 43914 -12
BBMak-Sooner_Or_Later_(Japan) 45078 -33264
BBMak-Sooner_Or_Later_(UK) 45250 -93604
Brie_Larson-Finally_Out_Of_PE 14163 -12266
Britney_Spears-Baby_One_More_Time 24254 -12
Cheyenne_Kimball-The_Day_Has_Come -12 -12
Christina_Aguilera-Christina_Aguilera 12724 -32087
Christina_Aguilera-What_A_Girl_Wants_(Single) 15301 -15511
Covent-Nexus_Polaris 17111 -7652
Dream_Theater-Metropolis_Pt_2_Scenes_From_A_Memory 24053 -1878
Dream-He_Loves_U_Not_(Single) 15445 -17251
Dream-It_Was_All_A_Dream 18256 -3148
Dream-This_Is_Me_(Remixes) 16825 -6995
Evanescence-Fallen 11468 -15763
Hilary_Duff-Santa_Claus_Lane 634 -12
Hoku-Hoku 15367 -4506
In_Flames-Come_Clarity 658 -12
JC_Chasez-Schizophrenic 15466 -3667
Jesse_McCartney-Beautiful_Soul -1160 -12
Jessica_Simpson-Sweet_Kisses 14755 -5378
Jump5-All_The_Time_In_The_World 636 -87648
Ks_Choice-The_Great_Subconscious_Club 19119 -5920
Lacuna_Coil-Comalies 45977 -118426
Lacuna_Coil-In_A_Reverie 45449 -120340
Lacuna_Coil-Unleashed_Memories 45502 -6635
LFO-Life_Is_Good 2 -12
Liberty_X-Thinking_It_Over 49261 -84313
Lindsay_Pagano-Love_And_Faith_And_Inspiration 15691 -6411
M2M-Shades_Of_Purple -12 -4804
Mandy_Moore-Candy_(Single) 17957 -3705
Mandy_Moore-Mandy_Moore 39136 -9195
Mandy_Moore-So_Real 722 -16303
McFly-Room_On_The_3rd_Floor -1160 -86372
McFly-Wonderland -12 -12
Mudvayne-The_End_Of_All_Things_To_Come 14537 -7110
No_Doubt-Tragic_Kingdom 14725 -3224
NSync-Home_For_Christmas 17234 -23933
NSync-No_Strings_Attached 7972 -4574
NSync-NSync 16831 -519
Opeth-Blackwater_Park 14799 -5383
O-Town-O2 698 -11294
Play-Dont_Stop_The_Music 15340 -5052
Play-Girls_Mind 16525 -13544
Play-Play 14018 -22647
Play-Play_Around_The_Christmas_Tree 636 -12
Play-Replay 37409 -44907
Play-Us_Against_The_World 16623 -16246
Sarah_McLachlan-Surfacing 8876 -2096
Stacie_Orrico-Genuine 15586 -3172
The_Gathering-Mandylion 46148 -7756
The_Kovenant-Animatronic 16903 -2445
Tool-Undertow -1157 -15455
VA-Kaerlekens_Spraak 24164 -29135
VA-Pixel_Perfect 670 -88212
VA-Radio_Disney_Holiday_Jams_2 15400 -3978
Winds-Reflections_Of_The_I -1160 -22

The numbers listed are offsets (with respect to the current EAC reference offset) needed to make the first track start on a non-zero sample, and to make the last track end on a non-zero sample, respectively. The start offsets can go no lower than -1160 for the start tracks, and no higher than +472 for the end tracks (these are the offsets of the drives I used to rip the start and end tracks, they can't overread). Most of the numbers aren't helpful because the beginning/end are padded with silence. There is only one number that sticks out to me which is -12 (3 CDs have that as their start offset, and 11 CDs as their end offset). There are no CDs with a -30 offset, so to me it seems pointless to change the reference offset when it's not going to bring any practical benefit.

This post has been edited by Moitah: Nov 24 2006, 12:48

[Martin H]

It's nearly always possible to get all the audio samples extracted from a CD-DA, even without using offset correction/overreading, and if it isn't, then it's just a matter of loosing some samples of background noise and not any real music, unless the mastering engineer has f***** up the mastering process. Now getting real "bit-perfect" extractions i.e. not only getting the audio samples extracted, but also the precise number of null samples extracted from the beginning/end of the first/last track also, is just not possible(except for some lucky few, which actually matches the choosen offset we are using), no matter if using Andre's or Ipsedixit's reference offset, since the first/last sample of each CD-DA isn't located at the exact same place, and instead starts/ends at highly varying sample possitions...

[Cosmo]

What does "bit perfect" mean to you ?

For me, bit-perfectness does not depends on offsets.

''Bit Perfect'' doesn't really mean anything to me, but I assume that most people who like to use that term intend it to mean a perfect 1:1 image. All I care about personally is accurate extraction of actual audio data. [edit] I mean actual music. I don't really care too much if silence is actually null samples or not. [/edit]

It seems that anyone who wants to change the current standard for offset correction does not understand the complete issue, or is jumping to a conclusion without sufficient proof that more accurate results can be obtained from a majority of CDs. Personally, I still wouldn't care. But at least there would then be a valid argument to be made.

[edit.2]

[...] then it's just a matter of loosing some samples of background noise and not any real music, unless the mastering engineer has f***** up the mastering process. [...]

Yeah... If a 30 sample skew meant that I'd actually miss something important, then I'd want to shoot the mastering engineer, not Andre.
[/edit.2]

This post has been edited by Cosmo: Nov 23 2006, 15:25

[greynol]

What part of this did you guys not read?

I can confirm that the way Ipsedixit calculated his offset is correct and gives an absolute result.
He captured the output of the optical sensor in a CD player and stored an image of the pit and lands of a given CD. He then produced a binary version of these pits and lands, then computed all the subcode extraction and audio deinterleaving with a custom software. Then he compared the result with an offset corrected extraction of the same CD.

Moitah's numbers are irrelevant here. I looked over Pio's test earlier and can tell you that it has nothing to do with the method that IpseDixit used.

As for reproducing the greatest amount of samples on a copy while still maintaining the same track lengths, it is important to take into account not only a drive's ability to overread but also it's ability to overwrite. In the case of Plextors with a read sample offset correction of 30 and a write samples offset of -30, you will always get a more complete copy without using a read sample offset correction or a write samples offset than you will using the currently accepted ones when duplicating a disc where this would make a difference. This is and has always been true regardless of where the "absolute" postition of the audio is.

This post has been edited by greynol: Nov 23 2006, 17:12

[Moitah]

I should have worded that last sentence differently. I don't doubt that his numbers are correct, rather that in practice it doesn't seem to matter.

[greynol]

I don't doubt that his numbers are correct, rather that in practice it doesn't seem to matter.

I agree, and it's minutia if you ask me.

My comment earlier about how spoon could reset the database was only an observation, BTW. I think I would actually prefer that AccurateRip remain the way it is. These issues regarding offsets and images can easily be managed by the user without the need for any changes to AccurateRip or its database.

...and FWIW I have a disc [The Rolling Stones - Aftermath (London 820 050-2)] that produces non-zero samples at least up to the 11760 sample limitation of EAC's GUI before the first track and produces non-zero samples after the last track at least up to 11759 samples (11760 gave me a missing samples error) using my PX-716. If anyone's interested, I can get more precise numbers by bypassing EAC's GUI as well as trying a different drive to check the lead-out to see if I can avoid the missing samples error.

Anyhow, I don't think I'll be able to make a "bit perfect" copy of this disc anytime soon.

Regarding the concept of skew, is it applicable to IpseDixit's test or is it only applicable to Pio's test?

This post has been edited by greynol: Nov 23 2006, 18:03

[bhoar]

I never understood this obsession with having a "bit perfect" audio CD copy.

Reference standards are useful. Without some sort of positional reference, AccurateRip wouldn't be possible, meaning it can be difficult to be sure a rip was correct (programmatically).

So far, no one I know of is arguing for a *real* bit-perfect copy of audio CDs, including bit-perfect copies of all the subcodes and error correcting code (some, but not all, of which will be automatically generated to similar values when writing a copy of the audio). Just all of the audio (excepting pre/post silence) and a standard to put the track/index marks in the same places across drives/rippers.

In rare cases, such as greynol's above, this may fail, but I think it handles 99.99% of CDs just fine.

Anyhow, I don't think I'll be able to make a "bit perfect" copy of this disc anytime soon.

...well, not with a single make/model of drive, at least.

-brendan

This post has been edited by bhoar: Nov 23 2006, 20:27

[Sebastian Mares]

I am a bit confused and hope that you can help me out. During the past months, I realisd that it's really nonsense to care about 6 or 30 samples at the end of a CD (at least for me). Anyways, I would like to understand this debate:

1: Is the true offset correction for drives always 30 samples less than now? Does this mean that most Plextors have a 0 samples read offset and that LITE-ONs need a negative read offset correction (meaning that they have to overread from lead-in)?

2: You say that for some audio CDs, the offset is different because different write offsets were used. Isn't the read offset of a drive always constant? What does it have to do with the write offset of a CD? For me, an 1:1 copy of a CD should be 1:1; if a CD has 40 samples of silence because of a write offset, the copy should also have 40 samples of silence, even if the actual audio data does not begin at sample 1.

[The Legioneer]

1: Is the true offset correction for drives always 30 samples less than now? Does this mean that most Plextors have a 0 samples read offset and that LITE-ONs need a negative read offset correction (meaning that they have to overread from lead-in)?

According to IpseDixit's industrial tests, yes. Whatever the previous offset was, subtract 30 to determine the new offset for your drive. So most LITE-ONs, that I believe were around +6, would now be -24.

2: You say that for some audio CDs, the offset is different because different write offsets were used. Isn't the read offset of a drive always constant? What does it have to do with the write offset of a CD? For me, an 1:1 copy of a CD should be 1:1; if a CD has 40 samples of silence because of a write offset, the copy should also have 40 samples of silence, even if the actual audio data does not begin at sample 1.

Except in rare cases of extremely old (and bad) drives, the read offset of your drive will always be constant. The main problem is that where the audio begins on a CD varies from disc to disc, making true absolute 1:1 extraction a very difficult thing. The read offset is a method to allow your drive to produce results identical to other drives, not the disc itself. The offset proposed by IpseDixit just moves the offset to a position on the disc where audio would begin if the disc was manufactured with absolutely zero skew, which is a pretty rare occurance. The offset calculated by Andre was where he found the audio to begin on most the discs he owned, which were more than likely manufactured with deviation from zero skew, thus making his offset an admitted estimate.

In real world practice, no matter which offset you use, Andre's or IpseDixit's, you won't have a perfect 1:1 copy for every disc.

[Sebastian Mares]

Ah, I see, so the problem is finding out how to detect read offset. So, are 0 samples write offset discs seldom?

This post has been edited by Sebastian Mares: Nov 23 2006, 21:59

[Pio2001]

For what it's worth, I used a method similar to the one described on Pio2001's page. I did it on 74 CDs, the results are here:

(...)

There is only one number that sticks out to me which is -12

Using my three old reference CDs, I find +44. One of them was made by DADC around 1990, one other by Interpress around 1988. And the third by one of these two.

Regarding the concept of skew, is it applicable to IpseDixit's test or is it only applicable to Pio's test?

What do you mean ?
The "main to subchannel skew" was introduced by RichMan in the CDFreaks thread about absolute offsets, but he then said that it was like Nero's offset correction : it can only be adjusted by an integer number of sectors.

1: Is the true offset correction for drives always 30 samples less than now?

Yes

Does this mean that most Plextors have a 0 samples read offset

Yes, according to the real reference.

2: You say that for some audio CDs, the offset is different because different write offsets were used. Isn't the read offset of a drive always constant? What does it have to do with the write offset of a CD? For me, an 1:1 copy of a CD should be 1:1; if a CD has 40 samples of silence because of a write offset, the copy should also have 40 samples of silence, even if the actual audio data does not begin at sample 1.

In order to get back exactly what was burned or pressed onto the CD, you must rip with exactly the same offset as the one that was used during the burning.

[Sebastian Mares]

In order to get back exactly what was burned or pressed onto the CD, you must rip with exactly the same offset as the one that was used during the burning.

Yes, if you want to get the exact data that was used during the burning process - but I want to get the exact data from the CD (like what a reader with a 0 samples read offset would get).

[Martin H]

The main problem is that where the audio begins on a CD varies from disc to disc, making true absolute 1:1 extraction a very difficult thing. The read offset is a method to allow your drive to produce results identical to other drives, not the disc itself. The offset proposed by IpseDixit just moves the offset to a position on the disc where audio would begin if the disc was manufactured with absolutely zero skew, which is a pretty rare occurance. The offset calculated by Andre was where he found the audio to begin on most the discs he owned, which were more than likely manufactured with deviation from zero skew, thus making his offset an admitted estimate.

In real world practice, no matter which offset you use, Andre's or IpseDixit's, you won't have a perfect 1:1 copy for every disc.

Exactly - Very well put

Cheers mate

[Pio2001]

but I want to get the exact data from the CD (like what a reader with a 0 samples read offset would get).

Is the pregap data part of "the data from the CD" ?
Is the lead-out data part of "the data from the CD" ?
Is the lead-in data part of "the data from the CD" ?
Are hidden tracks before track one part of "the data from the CD" ?

[Sebastian Mares]

I would answer all questions with "yes". Thing is, I have an LG unit with a 0 samples write offset. What I would like to be able to do is create a real 1:1 (excluding subcodes) copy of a CD.

[db1989]

Then, without manually checking pregaps and lead-in/out areas (which would surely be a tortuous process), your best bet would be to apply a -30 samples correction - if I understand correctly.

I agree with whoever said that this provides an updated reference, rather than anything else. If all manufacturers created CDs with no skew or fancy bits in non-standard areas, we wouldn't need to worry! I personally don't think that there's any guaranteed way to get everything from a CD without greatly increasing your workload.

However, although I'm the type to say "30 samples doesn't matter!", I'll probably get paranoid and start re-ripping anyway.

[Sebastian Mares]

Wondering about one thing... I remember burning a Nero CD/DVD Speed DAE test CD with my LG (that has 0 samples write offset) and tested my Plextor which was reported to have a read offset of 30 samples. How is this possible if the LG has 0 samples write offset? Does this mean that my LG now suddenly has a 30 samples write offset and that the Plextor has 0 samples read offset?

[benski]

Wondering about one thing... I remember burning a Nero CD/DVD Speed DAE test CD with my LG (that has 0 samples write offset) and tested my Plextor which was reported to have a read offset of 30 samples. How is this possible if the LG has 0 samples write offset? Does this mean that my LG now suddenly has a 30 samples write offset and that the Plextor has 0 samples read offset?

Yes. Because the write offsets were calculated based on the read offsets.

[greynol]

Anyhow, I don't think I'll be able to make a "bit perfect" copy of this disc anytime soon.

...well, not with a single make/model of drive, at least.

No, not with any combination of drives using any of the standard burning software. This is because there are over 20 frames audio data in the lead-in as well as in the lead-out.

2: You say that for some audio CDs, the offset is different because different write offsets were used. Isn't the read offset of a drive always constant? What does it have to do with the write offset of a CD? For me, an 1:1 copy of a CD should be 1:1; if a CD has 40 samples of silence because of a write offset, the copy should also have 40 samples of silence, even if the actual audio data does not begin at sample 1.

I'm not sure if you were addressing me, but I'll try to clarify what I wrote earlier. Drives using a negative write samples offset would require writing to what the drive believes to be the lead-out. This seems to be commonly accepted as impossible. It is certainly not possible with Plextor drives that have a write samples offset of -30 (per Andre's reference) using either EAC or Plextools.

This means that when using the classic write samples offset of -30, the last 30 samples of any burn will always be null. Simply put, if the last 30 samples of the last track in the source file aren't null they will be lost. Let's say that this same disc also began with samples that aren't null and these samples continued into the lead-in. If you were to use the new offset, you would be able to get an additional 30 non-null samples which you can burn. IOW, shifting the correction by -30 samples will allow a Plextor drive like a PX-760A to reproduce 30 more samples because instead of zero-padding the beginning of the data and prematurely ending at the lead-out which it cannot write beyond, there will be no zero-padding and the end of the data will conincide with the beginning of the lead-out.

The offset calculated by Andre was where he found the audio to begin on most the discs he owned, which were more than likely manufactured with deviation from zero skew, thus making his offset an admitted estimate.

I don't believe you can know what I have bolded with any certainty whatsoever. Where non-zero data begins isn't necessarily related to skew.

Pio wrote this in CD-Freaks:

This gives us three theoretical offsets, whose values differ by an amount of 324 samples. The fact that the offset that you found is only 30 samples away from Andre Wiethoff's one (that is itself 6 samples away from mine !) shows that both Andre's result and mine come from nonsensical data.

Also, from reading the thread over at cdfreaks, it seems that the skew is in sectors, not samples.

Regarding the concept of skew, is it applicable to IpseDixit's test or is it only applicable to Pio's test?

What do you mean ?

I hadn't read the cdfreaks article prior to asking the question. I was wondering if IspeDixit's determination of the read offset could be influenced by skew like the test that you, Andre and Moitah performed.

This post has been edited by greynol: Nov 24 2006, 20:31

[Sebastian Mares]

So Nero CD/DVD Speed also relies on EAC's calculation?

This post has been edited by Sebastian Mares: Nov 24 2006, 20:26

[benski]

So Nero CD/DVD Speed also relies on EAC's calculation?

I would assume that all CD reading/writing programs that implement offset support are based on EAC's calculation.
The only way to determine write offset is to burn a disc, and read it back, comparing the offset with the original burned data. Since the asbolute offset is in question, you don't really know if the write/read offsets at 0/0 or -30/+30 (or -X/+X)

This post has been edited by benski: Nov 24 2006, 23:02

[Sebastian Mares]

It is certainly not possible with Plextor drives that have a write samples offset of -30 (per Andre's reference) using either EAC or Plextools.

This means that when using the classic write samples offset of -30, the last 30 samples of any burn will always be null. Simply put, if the last 30 samples of the last track in the source file aren't null they will be lost. Let's say that this same disc also began with samples that aren't null and these samples continued into the lead-in. If you were to use the new offset, you would be able to get an additional 30 non-null samples which you can burn. IOW, shifting the correction by -30 samples will allow a Plextor drive like a PX-760A to reproduce 30 more samples because instead of zero-padding the beginning of the data and prematurely ending at the lead-out which it cannot write beyond, there will be no zero-padding and the end of the data will conincide with the beginning of the lead-out.

I know that when burning with a Plextor, I am going to lose 30 samples anyways. The scenario I am thinking of is that I have a drive with a 0 samples write offset (like the LG E10L as far as I know). My test with Nero CD/DVD Speed (burn test CD with LG unit, read with Plextor unit) showed that my PX-755A has a read offset of -30 samples (therefore it needs a read offset correction of +30 samples). If what was said previously regarding the correct read offsets being actually 30 samples off the current figures, this would mean that my Plextor has a 0 samples read offset, but that my LG has a 30 samples write offset.

This post has been edited by Sebastian Mares: Nov 24 2006, 21:21

[greynol]

If what was said previously regarding the correct read offsets being actually 30 samples off the current figures, this would mean that my Plextor has a 0 samples read offset, but that my LG has a 30 samples write offset.

Exactly. Now, the question is, will you be able to burn the first 30 samples of a disc correctly using your LG if they are not null?

A Plextor PX-760A configured with a write samples offset of 0 will be able to burn every sample without replacing non-null samples with null samples. In light of the new absolute read offset, these Plextor drives are already optimized and can be used with any burning program (besides PlexTools, lol) without first having to apply an offset since there is no need for calibration.

This post has been edited by greynol: Nov 24 2006, 22:41

[Sebastian Mares]

One more thing - do Plextors have a 0 samples read and write offset, or do they still have a -30 samples write offset?

[greynol]

One more thing - do Plextors have a 0 samples read and write offset, or do they still have a -30 samples write offset?

As benski already stated, the write offset will change along with the read offset.

The whole goal of offset correction (EDIT: from the copying perspective rather than from the rip comparison perspective) was to create a system by which audio data was shifted to produce a combined read and write offset of 0. If you shift the read offset in order to conform to a different standard, you much also shift the write offset.

The only point I'm trying to make is that the ability to create (or not create) sample perfect copies hasn't really changed.

This post has been edited by greynol: Nov 24 2006, 22:57