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Topic: Understanding CD TOCs and different pressings (Read 9652 times) previous topic - next topic
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Understanding CD TOCs and different pressings

Can someone explain to me what the CD TOC entails?

Is the CD TOC always the same for the same CD even if the pressing is different?

What differs in different pressings?

How does the CD TOC differ from the disc ID used by freedb?

How often would you expect collisions if using the CD TOC to identify unique disc (not counting pressings)?

Would CD TOC plus album gain be a good way to distinguish the same CD but remastered?

Understanding CD TOCs and different pressings

Reply #1 –
Quote from: Eli on
Is the CD TOC always the same for the same CD even if the pressing is different?

Your question is a bit confusing. No, for the same CD (album) the CD TOC is not always the same. If the TOC is different then the CD layout was done differently and it's generally called a different "issue" or "release", never called a "different pressing".

So yes, when speaking of "different pressings" then it's always the same TOC involved but with differeing audio data. This is because the "glitch" is introduced in the production of the glass master in the fab and not during creating the CD's layout, AFAIK. Manufacturers and/or models of glass disc mastering machines seem to use different offsets for the audio. I don't know if it's hardwired or adjusted in the fabs by some technicians. So the record company wants it to be A, and sends it (probably on digital tape back in the old days, then via HDDs and now via wire) to all the CD fabs. But every CD fab depending on what machines they use send back B or C, somtimes even D.

Quote from: Eli on
What differs in different pressings?

The offset of (most often) the entire disc. So most different pressings can become bit identical when you've found this offset skew and adjust your drive to it, or use a tool like CUETools to do this after the rip.

There are cases where (sets of) single tracks may have a different offset, but I've never seen such a case. I don't know if it's true or just a rumour.

Then there may also be manufacturing defects of the glass master in one of the fabs that lead to different results for single tracks, or worse, more tracks. I'd not call this a different pressing but rather a blooper.

Quote from: Eli on
How does the CD TOC differ from the disc ID used by freedb?

You can think of the disc ID being a hash calculated from the TOC.

Quote from: Eli on
How often would you expect collisions if using the CD TOC to identify unique disc (not counting pressings)?

The less tracks an audio CD has the more often it does occur. There are quite a lot of collisions for singles or albums with few but long tracks.

Quote from: Eli on
Would CD TOC plus album gain be a good way to distinguish the same CD but remastered?
Sure it would, but I think generally that the song entry points and gaps are often also re-edited with remasters. It's a bit more confusing with different issues of one album that were all released in the same year, but by different distributors or sub-divisions of the same distributor. Depending where in the world you buy the album you get a different issue. Sometimes the discs are 1:1 identical but other times they are "different pressings" or even had different (audio) mastering (hence replaygain is useful) together with a different TOC. I've seen it myself.

Understanding CD TOCs and different pressings

Reply #2 –
>Is the CD TOC always the same for the same CD even if the pressing is different?

Yes 100% identical.

Understanding CD TOCs and different pressings

Reply #3 –
Thank you for the replies. I am asking because I am trying to find the easiest way to avoid duplicate discs in my collection. I often buy lots of discs from ebay or yard sales. It would be nice to have software identify the disc as in my collection.

What is the best way to deal with singles? I assume the TOC (or CD Table of Contents) tells the number of songs and the length of those songs as well as any gaps, etc, right? I find it surprising that there are actually many collisions, but I guess there are alot of discs.

Understanding CD TOCs and different pressings

Reply #4 –
Except for HTOA, gap information cannot be found in the TOC.

There are more collisions with IDs generated for freedb because the times are resolved to seconds, not individual frames.  This obviously isn't true for the TOC.

Understanding CD TOCs and different pressings

Reply #5 –
The CUE generated from a disc has the gap information right?

Ok, so could TOC + CUE be a very good unique identifier with fewer collisions then TOC alone?

Is there anything else that could be used?

Understanding CD TOCs and different pressings

Reply #6 –
>The CUE generated from a disc has the gap information right?
Sure, but depending on the drive, the method and the condition of the disc, you might get different results.

>Is there anything else that could be used?
The Disc ID as calculated by AR, I suppose.  I may be wrong, but I think it might provide additional information for enhanced discs than just using the TOC.

Understanding CD TOCs and different pressings

Reply #7 –
Quote from: greynol on
>The CUE generated from a disc has the gap information right?
Sure, but depending on the drive, the method and the condition of the disc, you might get different results.


What if the drive reads HTOA and overreads, then CUEs should be accurate and consistent (if the disc is in readable condition), right?

Understanding CD TOCs and different pressings

Reply #8 –
Quote from: Eli on
What if the drive reads HTOA and overreads, then CUEs should be accurate and consistent (if the disc is in readable condition), right?
I don't think so, no.

Also, the ability to overread and read HTOA isn't going to buy you anything in terms of properly identifying a CD from its structure.

Understanding CD TOCs and different pressings

Reply #12 –
Different drives can give different results using the same method.  Different methods can give different results using the same drive.

There is no requirement that gap information must be present in every frame of a CD.

Maybe I should have said, depending on the drive, the method or the condition of the disc, you might get different results.

Understanding CD TOCs and different pressings

Reply #13 –
So the CUE sheets that everyone creates that does disc-as-one images are not necessarily identical depending on the disc, drive, or method?

Ok, what information does the CUE contain? Why would it not be consistent?

What information does the TOC contain?

Understanding CD TOCs and different pressings

Reply #14 –
Quote from: Eli on
What information does the TOC contain?

Quote
3.1.89. TOC Table of Contents - The TOC has information on the type of session and the starting address
of the tracks. This information is encoded in the Q Sub-channel in the Lead-in area.

3.1.56. Lead-in - On CD media it is the area that contains the TOC data and precedes each program area.
The main channel in the Lead-in area contains audio or data null information. This area is coded as
track zero. The Q Sub-channel in this area is coded with the Table of Contents information…
If age or weaknes doe prohibyte bloudletting you must use boxing

Understanding CD TOCs and different pressings

Reply #15 –
Ok, so does knowing the number and lengths of songs differ in any way from the CD TOCs information on the starting addresses?

Does anyone know what information the AccurateRip ID tag entails? How often would collisions be expected for it?

Understanding CD TOCs and different pressings

Reply #16 –
Geez, we've been over this already. This is the third thread about it, how many do you need? The format description in my post is just about what CD TOCs contain.

As for collisions, that's a problem that occurs with FreeDB because its hashing algorithm is weak. Although MusicBrainz's algorithm isn't strictly immune to possible collisions either, in practice it doesn't have that problem. While it might not be ideal (it doesn't include data tracks in the computation of its DiscID), it shows that CD TOCs contain enough information to reliably identify discs.

So far there hasn't been a useful comment on my proposal since I modified it last summer, based on the comments I got back then. At the time I had already implemented it for FLAC in my own set of scripts. It works. Unless people come up with new suggestions, I don't see what the hold up is. The specs are easy enough to implement, the code already exists in other forms (see ID3v2's MCDI tag), there's nothing preventing Spoon or anyone else to go ahead and add support for it in their apps. That includes Josh's reference FLAC encoder and tools; he already implemented RIFF preservation in a similar fashion (i.e. using METADATA_BLOCK_APPLICATION), he (or anyone else, it's Free Software after all) could very well do the same for CD TOCs.

Understanding CD TOCs and different pressings

Reply #17 –
skamp, this thread is not about how to store a CD TOC, its just me trying to understand a few things, such as TOCs, CUEs, ect and there differences.

I agree, I wish people would either make some usefull comments on your proposals or implement them. I think storing CD TOCs in the meta-data is very important.