Optical Storage - Upgrading and Repairing PCs - page 733

Ripping/Copying Discs
All optical drives can play Red Book-formatted CD-DA discs, but not all optical drives
can read CD-DA discs. The difference sounds subtle, but it is actually quite dramatic. If
you enjoy music and want to use your PC to manage your music collection, the ability to
read the audio data digitally is an important function for your CD (and DVD) drives be-
cause it enables youto much more easily and accurately store, manipulate, and eventually
write back out audio tracks.
To record a song from CD to your hard disk, it was once necessary to play the disc at nor-
mal speed and capture the audio output as analog, hence the need for the four-wire analog
audio cable connection from the rear of optical drives to your sound card. Fortunately, for
several years drives have supported digital audio extraction (DAE). In this process, they
read the digital audio sectors directly and, rather than decode them into analog signals,
pass each 2,352-byte sector of raw (error-corrected) digital audio data directly to the PC's
processor via the drive interface cable (ATA, SATA, SCSI, USB, or FireWire). Therefore,
no digital-to-analog conversion (and back) occurs, and you essentially get the audio data
exactlyasitwasoriginallyrecordedontheCD(withinthelimitsoftheCD-DAerror-cor-
rection standards). You would have essentially extracted the exact digital audio data from
the disc onto your PC.
Another term for digital audio extraction is ripping , so named because you can “rip” the
raw audio data from the drive at full drive read speed, rather than the normal 1x speed at
whichyoulistentoaudiodiscs.Actually,mostdrivescan'tperformDAEattheirfullrated
speeds. Although some are faster (or slower) than others, most perform DAE at speeds
from about one-half to two-thirds of their rated CD read speed. So, you might be able to
extractaudiodataatspeedsonlyupto28xona40xrateddrive.However,thatisstillquite
a bit better than at 1x as it would be on drives that can't do DAE (not to mention skipping
the conversion to analog and back to digital with the resultant loss of information).
Virtuallyallneweropticaldrivescanperformdigitalaudioextractiononmusicdiscs.How
fastoraccuratelytheydothisvariesfrommodeltomodel.Youmightthinkanyextraction
(digital copy) of a given track (song) should be the same because it is a digital copy of the
original; however, that is not always the case. The CD-DA format was designed to play
music, not to transfer data with 100% accuracy. Errors beyond the capability of the CIRC
in the CD-DA format cause the firmware in the drive to interpolate or approximate the
data. In addition, time-based problems due to clock inaccuracies can occur in the drive,
causing it to get slightly out of step when reading the frames in the sector (this is referred
to as jitter ). Differences in the internal software (firmware) in the drive and differences in
the drivers used are other problems that can occur.