How do current copy protected CDs work?

Discussion in 'Archived Threads 2001-2004' started by Eugene Hsieh, Jul 19, 2001.

  1. Eugene Hsieh

    Eugene Hsieh Supporting Actor

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    Re: This article on CNet.
    How does this copy protection work?
    It would be interesting to see what the technology is exactly. I do not understand how an audio distortion will prevent correct CD --> .wav copies, assuming the drive doing it does good quality rips. On the other hand I can see how certain types of sound distortion could wreak havoc with certain .wav --> .mp3 encoding algorithms, resulting in unwanted weird sounds. Of course, if the watermark is attacking this particular part of the process, then I'm sure that one can revise the encoding algorithms to compensate.
    Interestingly, this sounds a lot like when a crappy drive doesn't rip properly --> clicks and pops. However, I would be surprised if they were messing with the integrity of the disc storage method, because that would likely make the disc unreadable on some machines (like mentioned in the article).
    Which CDs have been copy protected?
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  2. Kevin P

    Kevin P Screenwriter

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    The article doesn't go into detail as to how it works (and I'm sure it's proprietary information anyway) but I'm guessing that they put intentional errors in the bitstream, that an audio CD player will interpolate (or drop) out, but when you rip the track on a PC, the errors remain as clicks and pops, much like when you rip a faulty or scratched CD.
    I'm sure someone will develop a workaround for this. But the gist of it is they're making CDs intentionally defective. I hope someone publishes a list of known "protected" CDs so we know to avoid them.
    KJP
     
  3. Jeremy Little

    Jeremy Little Supporting Actor

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    Isn't it possible that the cd player will not properly interpolate the disc and drop the errors. That would mean the possibility that you could hear the errors. I find that very disturbing. I mean, not every CD player is on the same level. Different quality D/A converters, laser pick-ups, etc.
    I don't think it will help. After all, how many DVD ripper programs are there? I don't condone doing such, but the have bypassed all current protections, I.E macro, region, and they even have DeCSS programs now. It only slows them down for a second.
     
  4. Matt Perkins

    Matt Perkins Stunt Coordinator

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    Kevin is exactly correct. For more information, see this article at Inside.com. (Unfortunately, you have to pay $0.40 to read it, since it's an archived article. Sorry ...)
     
  5. Christian Behrens

    Christian Behrens Supporting Actor

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    I don't like this trend at all, it looks like they are deliberatly taking a loss of audio quality over the customer's right to listen to the product. And not only the loss of audio quality disturbs me, but also the fact that some of those CDs will refuse to play on a computer.
    There are tons of situations where I would want to listen to my CDs on a computer CD-ROM. Not everybody's first move is to rip CDs they bought.
    Someone made the analogy to cut away pieces of pictures in museums to avoid them being robbed. Just great.
    Besides, didn't CD sales rise last year after all?!?
    My two cents...
    -Christian
    PS: Yes, I would also strongly wish to know beforehand whether the contents of a CD is altered from the specs. But I fear you'll only know after it's too late...
     
  6. Michael St. Clair

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    I'm skeptical. I wouldn't be surprised if they have come up with something that works on some reader/software combinations, I'll bet I can come up with a way to bit-for-bit rip any of these discs in 24 hours.
    I'd love to find out which discs use this. Funny how they aren't saying....probably because they don't want the bad PR of somebody publishing a hack within days of knowledge of the system.
     
  7. Thomas Newton

    Thomas Newton Screenwriter

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  8. Christian Behrens

    Christian Behrens Supporting Actor

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    Thomas,
     
  9. Mick Wright

    Mick Wright Second Unit

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  10. Kevin P

    Kevin P Screenwriter

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  11. Michael St. Clair

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    quote: Heck, I'm still mad about the fact that I cannot record the stereo tracks of my concert DVDs digitally to my MiniDisc for use on the road, travelling, etc. :-([/quote]
    http://www.totalrecorder.com
    Just take the WAVs and play them to your MD. There are other ways as well.
    This (using TR to record DVD soundtracks) has even been featured on ZDTV.
    [Edited last by Michael St. Clair on July 25, 2001 at 01:51 PM]
     
  12. Christian Behrens

    Christian Behrens Supporting Actor

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    Michael,
    Thanks for the info, but I won't have direct access to a system with digital in- and outputs for some time to come. Oh well, I'll live...
    -Christian
     
  13. Michael St. Clair

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    You don't need digital IO, just a DVD-Rom drive. While you play the movie (with output set to stereo), TotalRecorder will make a WAV file of the soundtrack.
     
  14. MichaelPe

    MichaelPe Screenwriter

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  15. Denton

    Denton Stunt Coordinator

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    "Isn't it possible that the cd player will not properly interpolate the disc and drop the errors. That would mean the possibility that you could hear the errors."
    You are absolutely correct! In fact, I suspect that some of the very best sounding CD players in the world will be the MOST likely to mute with these intentionally embedded errors.
    I also suspect that most of the early "copy-guarded" CD's are in the mainstream pop arena where they are least likely to be played on high end equipment. The record companies are sitting back, waiting to see if there will be higher return rates on these CD's. If there is not a higher rate, they'll declare victory and announce that the sound quality is "unaffected". And that will be a lie.
    The comments about the consumer's right to make copies for his own use are valid as well. I routinely make copies of my CD's on my PC burner for playback in the car. (Why risk the original?) And I really don't want to go back to making cassette mix tapes.
    I plan to boycott companies that make CD's that violate MY rights. Screw 'em.
     
  16. Kevin P

    Kevin P Screenwriter

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    Unfortunately, the record companies are being hush-hush as to what discs are "protected". Someone's going to have to publish an unofficial list, based on ability/inability to rip copies of CDs that were recently released.
    Then we'll know what discs to avoid/return/find a workaround for.
    KJP
     
  17. Jeff Ulmer

    Jeff Ulmer Producer

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  18. Kevin P

    Kevin P Screenwriter

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    quote: All CD players use error correction...[/quote]There is actually two levels of "error correction" in CD players.
    The first level (called CIRC) is a redundancy code used to detect errors, and in the case of minor errors (ones of only a few bits), actually correct them. Errors corrected at this level cause NO degradation in the sound, since the bitstream is fully recoverable. I would expect CD-ROM drives also correct these errors on the fly when ripping tracks (though it's possible some cheapo ones don't).
    The next level kicks in if the CIRC can't correct the error, in the event that too many bits are lost to reconstruct them. This results in the loss of several consecutive samples (a fraction of a second, something like 1/70 of a second if I recall). Depending on the player, this sort of error may be handled by interpolation (filling in the gap by estimation, based on the samples immediately before and after), by simply muting (causing a very brief dropout), or it may simply pass the error through uncorrected, resulting in a click or pop (though I doubt that many audio CD players do this). However, most ripping software doesn't do the muting or interpolation on uncorrectable errors, so such errors result in a click or pop in the ripped track. That's what this "copy protection" scheme relies on.
    The way to find out how CD players react to the protection, is to find a CD that is protected, make a copy of it (to find out where the "errors" are), then play those segments (original, not the copy) on different CD players. Those that interpolate will likely have minimal degradation (unless they go overboard with the error count), but those that mute (like my boom box) will likely hear dropouts. And if CD players do exist that pass the bitstream uncorrected, well, the original's going to sound as bad as the ripped copy...
    KJP
    [Edited last by Kevin P on August 03, 2001 at 02:38 PM]
     

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