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Audio CD Perfection

Postby Tonearm on Sun Mar 30, 2003 1:57 pm

Hi, I've posted before about my Audio CD project which basically consists of making perfect copies of Audio CDs. I was planning on using the standalone Marantz CDR-500 for this purpose, but I'm now considering using a computer burner. I'm very concerned with making "perfect" copies of the CDs. Will I be able to do this with a computer burner? Basically I'd like to be able to extract audio data from a CD, burn it to a blank CD-R and then be able to verify that I have a perfect copy of the original CD. I'm sure there are one or more pieces of software that will allow me to do this. Can someone point me in the right direction?

Also, would this method be able to preserve the "negative track space" that exists at the beginning of certain tracks of some audio CDs?
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Postby cfitz on Sun Mar 30, 2003 2:46 pm

I hesitate to offend audiophile purists, but yes a computer CD-RW drive can. Here are some starting points:

Exact Audio Copy (EAC)
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CDex
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PlexTools (for use with Plextor drives)

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Postby Tonearm on Sun Mar 30, 2003 3:06 pm

Cool, thanks cfitz. Is there a tool that enables you to verify that you have a perfect copy of the original CD? Maybe incorporating a checksum (I'm not sure how those work) or something?
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Postby tazdevl on Mon Mar 31, 2003 3:19 am

If it's digitally encoded, aka CD, I see no reason to disagree with your statement. It's all 0's and 1's. Any CD copy program can accomplish it, you don't need anything special and several includ a CRC check or an option to verify the written data (Nero has the latter on the burn option screen).

Just making a perfect copy doesn't make much sense unless you're selling copies to the public. If you're not using an audiophile quality system, probably wouldn't hear the difference anyway.
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PlexTools & EAC

Postby Halc on Mon Mar 31, 2003 3:33 am

Only PlexTools and EAC offer high statistical guaranty that the copies you have made are exact copies of the original, including any cd-drive offset.

CloneCD, Alcohol and other related 1:1 bit-accurate programs can only copy CD-ROM (not Audio CD, which is a different standard) to a high degree of statistical accuracy.

Please understand that the reading of Audio CD is (due to many factors) not totally a deterministic process, even if you have only one reader and only one disc. There might be differences from one read to another, even if the reading drive and the disc remain the same.

As such, audio cd rippers can only try to achieve as high level of statistical accuracy as possible.

This accuracy is based on the performance of the cd-rom (or dvd or cdrw) drive, the printing of the disc (data level errors, pressing errors, dirt & scratches) and the program that controls the ripping process (such as EAC).

As for tools of checking, I'd suggest you use Exact Audio Copy's various utilities such as: "Test & Copy" or "Compare Wavs".

They will check the contents of a cd or two wavs (respectively) for bit level matching.

regards,
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Postby Tonearm on Mon Mar 31, 2003 2:20 pm

What process do you go through to verify that you are making as close to perfect audio CD-Rs as possible? I guess that's basically what I'm asking. I'm trying to set up a process I can go through to accomplish this. I would guess it would be something like:

1. rip image
2. verify image
3. burn image
4. verify burned CD-R

I guess EAC could be used to do all of these things, right? What about hardware? Are there certain characteristics I should look for in a CD ripper/burner? It seems like you don't have to wonder if your hardware is doing a sufficient job because of #2 and #4. You would know for sure either way right?
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Postby Halc on Tue Apr 01, 2003 5:51 am

Tonearm,

things to look for in the hardware:

1) As high statistical accuracy as possible in reading and correctly reporting C2 errors via the MMC command set (LiteOn 52x CDRW is the best of the ones tested at the time of writing this)

2) A good ability to read scratched sectors from an audio disc withoug marking them unreadable (again the previously mentioned LiteOn is pretty good in this regard)

3) Minor read and write offsets (again the same LiteOn)

4) Ability to read into the lead-in and lead-out of audio tracks
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Postby Tonearm on Tue Apr 01, 2003 11:57 am

Halc, I've been hoping I could get the internal CD-RW drive for my laptop. From what I've read at exactaudiocopy.de, it seems like even if this drive can't report C2 errors, does caching, doesn't have accurate stream, and isn't very accurate with DAE I'll still get the same results as I would with a drive like the LiteOn but it will just take longer. The way EAC works in secure mode makes it seem like it *will* get the information right, it just may have to read the same sector 82 times to get there if the drive isn't as accurate.

I suppose if the drive can't read subchannel data I'll be out of luck as far as pre-track gaps though.

Do I have this down right?

Also, what is reading the lead in and lead out for?
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Postby Tonearm on Tue Apr 01, 2003 12:00 pm

Also, I don't plan on burning any scratched CDs at all. I'll be repairing any scratches on any CD I rip with the CD Playright kit.
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Postby Halc on Fri Apr 04, 2003 3:45 am

Tonearm,

it's not quite as simple as that.

Two drives can have different capabilities in reading scratched parts of dics (the performance of their optical pathway / servo mechanism). THis regardless of whether they do C2 accurately, have accurate stream or Cache or not.

So, in theory, you should be able to find a drive that can read even the most scratched discs with the lowest number of errors.

The problem is that there doesn't exist a standard measure to test this kind of performance.

Some of the best I've seen are done right here at CR Labs with their reading tests of scratched CDs.

You should find a cd reader that is able to read as much of a scratched test disc without labeling any block/sectors unreadable (uncorrectable errors).

Please note that due to the fact that EAC (AFAIK) doesn't inclue C2 level correction mechanisms in itself, the performance of the C2 error correction mechanism of the drive itself will also come into play.

So, the drive's ability to read a test disc correctly is a combination of the optical/servo performance + the intelligence of the firmware controlling them + C2 error correction iimplementation = amount of damaged block that can still be read and corrected properly.

regards,
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Postby Tonearm on Fri Apr 04, 2003 11:40 am

Interesting.... I do plan on polishing up every disc I read with the CD Playright Kit so I shouldn't be reading any scratched discs. Are C2 errors always the result of a scratch or can they be in perfect-condition CDs? Can the PlexTools software do C2 error correction?
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Postby cfitz on Fri Apr 04, 2003 12:15 pm

Tonearm wrote:Are C2 errors always the result of a scratch or can they be in perfect-condition CDs?

C2 errors can and do occur for a variety of reasons, and you can have C2 errors on a disc with no scratches at all.

Tonearm wrote: Can the PlexTools software do C2 error correction?

C2 error correction is always done by the drive's firmware inside the drive, not in external programs. There isn't enough information returned from the drive to allow C2 error correction to be done externally. The best any external program could do would be to note where uncorrectable C2 errors occurred, if the drive supplies such information (not all do), and attempt to re-read those sections of the CD in the hopes of getting an error-free read.

This is essentially what EAC does. It reads multiple times to get the correct data. If the drive doesn't support C2 error reporting, then EAC can't know which areas of the disc are problematic and need to be re-read specifically, and thus it has to re-read the entire disc. This is a slower and less confident process. It is slower because the same data needs to be read again and again. It is less confident because there is no additional, explicit indication of an error that needs to be corrected.

An external program could also attempt to identify the exact samples that went bad and guess at what the correct values should be by averaging adjacent good samples. Some drives do this internally as well. It is known as masking or interpolation. Naturally, this isn't the optimum solution since it is only an imperfect attempt to reduce the effects of the errors, not to correct them altogether.

In summary, it is better to get a drive that does a good job of DAE in the first place rather than to rely on making up for shortcomings later via external software.

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Postby Tonearm on Fri Apr 04, 2003 12:47 pm

It sounds like C2 error correction is an attempt to end up with a better CD than you started with. Non-existent C2 error correction would still leave you with a perfect copy of what you were copying wouldn't it?
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Postby cfitz on Fri Apr 04, 2003 12:58 pm

No. If you have uncorrectable C2 errors on an audio CD, you are not getting a perfect copy of the original.

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