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Old 30th September 2012, 13:38   #1  |  Link
NeonMan
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A very strange case of Audio CD

Hi!
I was ripping my cd collection when I stumbled on a batch of mix CDs. I started riping them when I found a CD-R which I was unable to read correctly on the PC. I remember I had that exact problem time ago, it was posible to reproduce the CD-R on dedicated CD harware, but most PCs had trouble even reading the first track.
  • When playing the disk on a (second generation?) technics player, the audio is fine but the timestamp is all garbled-up, timecodes shifting forward and backwards.
  • When playing on windows, only the first track is played (both WMP and VLC).
  • On linux, IOerror is trown when trying to read the disk.
  • Recorded by a friend who made the mix. Likely ~5 years ago.

I want to dump the disk contents, more out of curiosity about how could someone copy-protect a CD-R years ago.

Is there a way to dump very low-level information from the disk? (subchannel, frames with wrong checksum, etc..).
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Last edited by NeonMan; 30th September 2012 at 14:17. Reason: Title
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Old 30th September 2012, 13:55   #2  |  Link
LoRd_MuldeR
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Well, all the "copy protection" schemes that have been "invented" for Audio CD's are pretty much based on the same idea: Pervert the built-in error-correct scheme! This means they intentionally add bit-errors to the original disc. And they increase the error-rate up to the point where (most) stand-alone players will still be able to recover the errors via forward-error-correction, i.e. restore the "correct" data bits from the redundant coding even in presence of "low level" bit-errors. CD-ROM drives, on the other hand, (additionally) use backward-error-correction, i.e. they try to read again and again and again until all the data was received correctly. Now the "hope" of the producer is that most (certainly not all!) standalone CD players will still be able to play such an "intentionally damaged" disc without noticeable playback interruptions, while CD-ROM drives trying to rip the disc will deadlock in an infinity "read failure -> try again" loop.

Now about your five-year-old CD-R: This one is probably damaged by the "normal" aging process and/or because of scratches, which might have a similar effect as the "copy protection", but has not been added intentionally

I would try to rip the CD with EAC. Maybe experiment with the various modes it offers! Also it may be worth trying different CD-ROM drives, if you have more than one drive/computer available. And don't forget to (carefully!) clean the disc...


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Title should be a very strange case of Audio CD but i cannot edit it now :P
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Last edited by LoRd_MuldeR; 30th September 2012 at 14:10.
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Old 30th September 2012, 14:22   #3  |  Link
NeonMan
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I remember having problems back then but never cared since my only player could read them. I don't discard aditional errors by the decay of the disk so IIRC this was intentional.
What catches my eye is that the copy protection is effective on recordable media. How could someone make such a disk with off-the-shelf cd recorders?
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Old 30th September 2012, 14:36   #4  |  Link
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As explained before, the Audio CD ("Red Book") never had any "copy protection" in its design. The "copy protection" that was "added" later is nothing but the intentional induction of read errors. Put simply, they give you a disc that is "damaged" in a way that will cause your CD-ROM drive to fail (because it is built for "try again until it succeeded perfectly - or give up"), while most standalone players will be able to cope with the mess (because they are built for "try as good as possible, but go on!"). Now your CD-R very likely has not been spoiled with a "copy protection" (intentional damage), but it is damaged anyway. And thus it shows an effect similar to "copy protection". The cause of the damage can be bad CD-R media, bad burning equipment, disc aging, scratches, and so on. It's not unusual for CD-R media to fail after a few years, especially if you use "cheap" discs. And even "fresh" discs can have relatively high error rate, e.g. when it has been burned with very "fast" speed.
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Last edited by LoRd_MuldeR; 1st October 2012 at 20:49.
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Old 1st October 2012, 00:50   #5  |  Link
NeonMan
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Correctly extracted with EAC (Burst mode, no error correction, ASPI).

Thankyou
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Old 1st October 2012, 12:43   #6  |  Link
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Protecting a CDR was not a big deal even 5 years ago ...
however I believe you have a defective CDR as already mentioned before.
EAC in burst mode is very unsafe - and should be used carefully.
Anyway, should you believe the Technics plays it correctly (which I don't believe - should it be defective then the Technics interpolate the missing/defective data), you may try to copy it using the digital out.
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