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How do current copy protected CDs work?


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#1 of 18 Eugene Hsieh

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Posted July 19 2001 - 03:16 AM

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 of 18 Kevin P

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Posted July 19 2001 - 03:53 AM

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 of 18 Jeremy Little

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Posted July 19 2001 - 04:52 AM

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.
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#4 of 18 Matt Perkins

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Posted July 19 2001 - 04:54 AM

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 of 18 Christian Behrens

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Posted July 19 2001 - 06:55 AM

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...
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." (Benjamin Franklin)

#6 of 18 Michael St. Clair

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Posted July 19 2001 - 07:40 AM

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 of 18 Thomas Newton

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Posted July 19 2001 - 11:43 AM

Quote:
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.

Even if your first move after buying a disc is to extract the audio, there is nothing wrong with that as long as you do it for your own personal use. Making compilation CDs, making backup CDs (where you fear theft of / damage to the original), and using a computer to serve as a jukebox are all legitimate applications. This type of copy protection interferes with them at the same time it adds supposedly inaudible (where have we heard THAT one before?) defects to the product.

Also, the Constitution does not let the Government grant copyright monopolies of infinite length. When the music on CDs (and DVD-Audio discs, and Super Audio CDs) falls into the public domain, the public should be able to extract it and use it freely. Copy protection interferes with that -- robbing the public of some of the value for which it had granted the copyright incentive in the first place.


#8 of 18 Christian Behrens

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Posted July 23 2001 - 07:03 AM

Thomas,
Quote:
Even if your first move after buying a disc is to extract the audio, there is nothing wrong with that as long as you do it for your own personal use.
Yes, I know that, and you're perfectly right, of course.

However, with my statement about ripping CDs I implied (as does the music industry) ripping for distribution (friends, Napster-like services, whatever).

It just looks like that the industry wants to take full control over how their products is used *after* they have already gotten the consumer's money, with no regard for the consumer's rights.

A look at the digital delivery services currently set up shows that pretty clearly: you can download music tracks in the format that they offer you, you pay a hefty price for it, and cannot even burn them on CD or even listen to them on another machine (and that's not even taking into account upgrading your computer's hardware. The music you paid for will be rendered useless).

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. :-(

-Christian

[Edited last by Christian Behrens on July 23, 2001 at 04:44 PM]
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." (Benjamin Franklin)

#9 of 18 Mick Wright

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Posted July 23 2001 - 10:32 AM

Quote:
I'll bet I can come up with a way to bit-for-bit rip any of these discs in 24 hours.

No need, just use exact audio copy in the error correcting secure mode.
"What the eyes see and the ears hear, the mind believes."

#10 of 18 Kevin P

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Posted July 24 2001 - 03:10 AM

Quote:
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.
This is exactly true. Most better CD players will interpolate out errors--basically they "fill in the gaps" using the information on either side of the gap--but a lot of cheap players (portables, boom boxes, mini-systems, car decks, etc.) will likely just insert a drop-out at the point where the error occurs. If the errors are one sample long, they will likely be inaudible (unless you are listening really carefully), but if they F&^* up multiple samples in a row it will likely cause a very noticeable drop out. If a cheap CD player doesn't detect, interpolate, or drop out the error at all, then you'll get a click or pop. Then add in REAL errors (caused by manufacturing defects, scratches, or smudges--these happen on ALL CDs), and you might push the CD player over its edge in terms of error correcting ability.

Heck, they might as well just pre-scratch the CD before putting it in the package. There, now they can't copy it! Posted Image

KJP


#11 of 18 Michael St. Clair

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Posted July 25 2001 - 06:49 AM

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 of 18 Christian Behrens

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Posted July 26 2001 - 01:06 PM

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
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." (Benjamin Franklin)

#13 of 18 Michael St. Clair

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Posted August 01 2001 - 06:05 PM

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 of 18 MichaelPe

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Posted August 02 2001 - 02:39 AM

Quote:
http://www.totalrecorder.com

Or, check out this thread for another alternative.

#15 of 18 Denton

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Posted August 03 2001 - 12:55 AM


"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.
"Watching television is like taking black spray paint to your third eye." Bill Hicks

#16 of 18 Kevin P

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Posted August 03 2001 - 03:02 AM

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 of 18 Jeff Ulmer

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Posted August 03 2001 - 04:21 AM

Quote:
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.

Do you have any proof to back up this claim? All CD players use error correction, and from the condition I've seen hundreds of used CDs end up in, that error correction is being used all the time with no perceived degradation in the sound.

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#18 of 18 Kevin P

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Posted August 03 2001 - 07:21 AM

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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