Hardware Reference
In-Depth Information
same: You are prevented from making normal copies, or the copies don't work properly.
In the case of music CDs, the copy protection can be quite obtrusive, adding noise to the
recording, and in extreme cases preventing the disc from even playing in a PC drive.
Several copy protection schemes are available for CD-DA (digital audio) discs, ranging
from the simple to sophisticated. The most popular protection scheme for digital audio
discs is called SafeAudio by Macrovision. Macrovision won't explain exactly how
SafeAudio works, but it purchased the technology from a company called TTR Techno-
logies and patents filed by TTR describe the scheme in detail. According to the patents,
the disc is deliberately recorded with grossly erroneous values (bursts of noise) in both
the audio data and the codes, which would typically be used to correct these errors. When
the disc is read, the normal error-correction scheme fails, leaving small gaps in the music.
When this happens on a standard audio CD player, the gaps are automatically bridged by
circuitry or code in the player, which looks at the audio data on either side of the gap and
interpolates (guesses) the missing values. The CD drive in a PC can do the same thing, so
the interpolation occurs only when playing CDs in an audio player mode. However, the
drive in a PC does not perform this same interpolation when “ripping” the data—that is,
copying it directly to a hard drive, another CD, or some other medium. In that case, the
unbridged gaps are heard as extremely loud clicks, pops, and noise. Both TTR and Mac-
rovision claim that the interpolation that occurs when playing a SafeAudio disc is not dis-
cernabletothehumanear,butmanyaudioexpertsdisagree.Toanaudiophile,theaddition
of any distortion or noise to the audio signal is unconscionable, plus you can't make legal
backups of your music—something that is allowed by law. Because of these problems, I
recommend avoiding the purchase of audio CDs containing SafeAudio or any other form
of copy protection.
CD Digital Rights Management
Digital rights management (DRM) goes a step beyond standard copy protection by spe-
cifying what you can and cannot do with a recorded CD or other type of commercial me-
dia. When applied to downloaded music, for example, DRM features in audio tracks can
prevent youfromburningasongtoCDanunlimited amount oftimes, playing asongpast
a particular date, or limit the number of times you can copy a song from one PC to anoth-
er.
Although the use of DRM on CD media (as opposed to downloadable audio tracks) has
been rare, the Sony rootkit scandal of 2005 is a useful case to keep in mind.
Sony BMG, one of the biggest music CD distributors, introduced a controversial method
of copy protection and DRM in the fall of 2005 by adding copy protection and DRM to
some of its music CDs. Affected CDs used either XCP (Extended Copy Protection, deve-
