Hardware Reference
In-Depth Information
the consumer music recorders look for. Built into the price of the AHRA-compliant media is a royalty
for the music industry that this track protects. The media costs about 20%-30% more than what
regular CD-R/RW media costs. If you try to use standard non-AHRA-compliant CD-R/RW discs in
these drives, the drive refuses to recognize the disc. These music devices also refuse to copy data
discs.
Note that this does not apply to the optical drive you have installed or attached to your PC. It does not
have to be AHRA compliant, nor does it need to use AHRA-compliant “For Music Use” media, even
if you are copying or recording music discs. Additionally, you can make digital copies of copies—the
SCMS does not apply, either. The bottom line is that you do not have to purchase AHRA-compliant
discs for the optical drives in your PC. If you do purchase such discs, despite the “For Music Use
Only” designation, AHRA-compliant discs can be used in your optical drives just as regular CD-
R/RW discs can be used for storing data. The extra information indicating AHRA compliance is
simply ignored.
CD Copy Protection
Worries about the public copying of software and music CDs has prompted the development of copy
protection techniques that attempt to make these discs uncopyable. There are different methods of
protecting software CDs versus music CDs, but the end result is the 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 the 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 Technologies 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 Macrovision claim that the interpolation that
occurs when playing a SafeAudio disc is not discernable to the human ear, but many audio experts
disagree. To an audiophile, the addition 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 specifying what
you can and cannot do with a recorded CD or other type of commercial media. When applied to
downloaded music, for example, DRM features in audio tracks can prevent you from burning a song
