Hardware Reference
In-Depth Information
you essentially get the audio data exactly as it was originally recorded on the CD (within the limits of
the CD-DA error-correction 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 which you listen to
audio discs. Actually, most drives can't perform DAE at their full rated 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 extract audio data at speeds only up to 28x on a 40x
rated drive. However, that is still quite 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).
Virtually all newer optical drives can perform digital audio extraction on music discs. How fast or
accurately they do this varies from model to model. You might think any extraction (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.
Note
When extracting (ripping) music from CDs, the default format is uncompressed WAV;
however, other compressed formats such as MP3 can be used as well. Because WAV files
match the high 44.1KHz sampling rate used on the CD, you have 176,400 bytes per second of
sound information, which means 1 minute of music consumes nearly 10.6MB worth of space on
your hard drive. MP3 compression can reduce that by a factor of 6 or more, with little to no
perceptible loss in quality when maximum quality (320Kbps) sampling is used. I recommend
that you rip media at maximum quality, and then reduce the media quality (and size) when
synchronizing to portable devices if storage space on the portable device is an issue. MP3 is
supported by all media players, while its chief rival, Windows Media Audio (WMA), is
designed for playback on Windows-based systems.
“For Music Use Only” CD-R/RW Discs
According to the Audio Home Recording Act of 1992, consumer CD recordable drives and media
sold specifically for recording music are required to have specific safeguards against copying discs,
mainly SCMS. That means these recorders can make digital copies only from original prerecorded
discs. You can copy a copy, but in that case, the data being recorded goes from digital to analog and
back to digital on the second copy, resulting in a generational loss of quality.
The media for these recorders must be special as well. They work only with special discs labeled
“For Music Use,” “For Audio,” or “For Consumer.” These carry the standard Compact Disk Digital
Audio Recordable logo that most are familiar with, but below that, as part of the logo, is an added
line that says “For Consumer.” These discs feature a special track prerecorded onto the disc, which
