For Your Ears Only

Retrofitting a long-established technology with copy controls is hard, but it can be done

5 min read
Illustration: Greg Mably
Illustration: Greg Mably

That new CD by the Seedless Tomatoes really rocks! You bought it, and you’re ready to “rip” it into an MP3 audio file for your pocket-sized MP3 player and maybe burn a copy for the car's CD changer, too. Hey, go ahead, it’s yours, right? Well, music lover, enjoy that unrestricted freedom while you can. Ripping CDs could become impossible—perhaps illegal, as well.

When CDs were first marketed in the mid-1980s, consumer digital recording of any kind was far enough in the future that the implications of unprotected content were barely considered. No one had heard of the Internet.

“Burn, baby, burn”

special report copy protection graphic

But after recordable CDs hit the market in 1991, momentum on copying the discs began to build. Copies of original CDs were perfect and could themselves be copied ad infinitum. When blank disc prices dropped, people began copying CDs for their friends, just as they had with cassettes.

Adding to the ease with which copied discs could be exchanged was the rise of the Internet and the increasing availability of unlimited access to it. That access, coupled with the widespread use of MP3 audio-compression technology, enabled the swapping of music files on a scale never before envisioned. (MP3 technology is based on layer 3 of the MPEG-1 standard, which describes the sound channels of digital video transmission.)

Recording companies began looking for ways to put the genie of infinitely copyable digital music files back into the bottle.

One of the factors the companies focused on first was the original standard that defined the CD audio format in 1980, known as Red Book. Created by Sony Corp. (Tokyo) and Royal Philips Electronics NV (Amsterdam, the Netherlands), Red Book has only one provision that allows for copy protection, the serial copy management system. This consists of a few copy-generation control bits slipped into the digital stream. Intended to prevent digital audio tape (DAT) recorders from making copies of copies, it has no effect on PCs.

Since the Red Book standard is well entrenched, with virtually all audio players built to its specifications, little room is left to implement additional copy protection of CDs. Nonetheless, the recording industry is tinkering with the underpinnings of the CD format itself while trying to disturb normal playback on CD players as little as possible.

All the protection systems used today exploit several key differences between audio players and the CD-ROM drives of computers. The goal is to prevent the unrestricted reading of audio data to a PC. Audio players, for instance, interpolate over data-read errors, such as those caused by scratches, making it possible for copy protection schemes to introduce correctable errors that shouldn't be audible but confuse CD-ROM drives. Such drives do not interpolate over errors; their primary use, storing computer files and applications, requires essentially perfect recovery of recorded data. When reading audio discs, they extract the data, byte by byte, even if it's in error. If lots of errors accrue, the result is a badly flawed, unlistenable music file—exactly what the record labels want if a CD has been copied.

Adding deliberate errors to the CD master would seem to be a perfect solution since it can be done within the Red Book framework. But if enough errors are introduced to ruin CD-ROM-drive ripping, the interpolation may become audible on CD players. In fact, if a CD bears enough bad data, the player may mute, skip, or even stop. So a balance must be struck between playability and protection.

A protection device now being used on nearly 60 million discs already sold is Cactus Data Shield, produced by Midbar Tech (Tel Aviv, Israel, now a subsidiary of Macrovision Corp., Santa Clara, Calif.). To obstruct ripping, Cactus alters the CD’s table of contents, which points the player to the individual tracks, in ways especially difficult for CD-ROM drives to resolve.

Cactus also adds a data “session,” an extra track that only CD-ROM drives will find. When you try to play the CD on a computer's drive, the alterations to the table of contents make software players like Windows Media Player unable to locate the first audio track, causing the PC to load a proprietary player contained in the data session. That player will play the audio at a greatly reduced bit rate, and will not let you copy it.

Other protection schemes, like Macrovision’s SafeAudio, alter the Reed-Solomon error-correcting codes normally used to ensure accurate data recovery. The alterations cause most CD-ROM drives to reject the related pieces of data. Playability is again at issue because CD players vary widely in their ability to accept apparently bad data. Some will play a flawed CD just fine, some will mute during extended interpolation attempts, and some will give up and quit.

What’s more, adding errors may shorten the life of a CD because it reduces the capacity of players to interpolate over errors from accumulated dirt and scratches. SafeAudio-encoded CDs have also been known to lock up computers and even require sending Apple Macintoshes, which do not consider these a recognizable format, out for repair to remove a stuck disc.

With Macrovision's recent acquisition of former rival Midbar, though, SafeAudio is being supplanted by Cactus Data Shield. While Cactus also introduces some errors, it flags them as control data, making them a little less likely to do damage because control data can more easily be ignored when playing a CD than can audio bits.

With full compatibility of copy protection schemes and Red Book players always in question, Philips, the co-inventor of the CD standard, has denounced any deliberate deviation from it. The company insists that altered discs not be permitted to carry the official CD logo or be called CDs.

’Twixt rock ‘n’ roll and a hard place

As both a major consumer electronics maker and a content provider, Sony, which co-established Red Book, also offers the Key2Audio protection system. While promising no changes to the audio bit stream, and thus no audio degradation, Key2Audio relies on a separate data session and some fiddling with the disc's table of contents to confuse PCs.

But early versions of Cactus and Key2Audio have been thwarted by users who obscured the data session, which is near the edge of the disc, simply by scribbling over it with a felt-tip pen. To prevent further manipulation, both Midbar and Sony have new versions of their products that make the line between the data and audio sessions visually indistinguishable, so that the data session cannot be easily marked.

“Publishers have had a lot of success at getting copy controls into new standards.”
—Seth Schoen, staff technologist, Electronic Frontier Foundation

A new entrant into the fray is Microsoft Corp. (Redmond, Wash.) with its new Second Session technology. This adds an extra data session containing Windows Media Player files and a set of rules for their use. Some record companies are considering including it on CD releases later this year.

Still, given the open nature of Red Book’s digital audio, and the widespread file swapping on the Internet, it's unlikely that today’s music can be protected. It takes only one person with a digital CD player-to-PC connection to rip songs and spread them around. And, of course, all these protection methods address only digital data streams. A good analog transfer, easily made by connecting a CD player’s audio outputs to a computer sound card's audio inputs, sounds indistinguishable from the original. It creates a swappable file that neatly bypasses all the schemes.

Some digital copying is still possible, but, as with the analog method, only at the actual, real-time playback speed of the CD. As Eyal Shavit, Macrovision's senior director, technology strategy, explains: “If you take a Cactus CD, and you have a Sony/Philips digital interface format output, you will be able to get the content that way. There is a way to prevent such copying, but right now it is not a major concern.”

In time, new standards, like DVD-Audio and Super-Audio CD, both of which offer superior sound quality and leave the Red Book format behind, will contain robust copy protection, putting the issue to rest. Says Seth Schoen, staff technologist at the Electronic Frontier Foundation in San Francisco: “Publishers have had a lot of success at getting copy controls into new standards. They're not having very much success retrofitting copy controls into existing standards.”

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