The availability and relatively low cost
of CD recorders and recordable media has put custom compilation audio
CDs within the reach of many users. Since the inception of audio CDs,
users have desired the ability to create their own custom CDs while
keeping the quality of the music that digital recording provides.
Digital audio extraction makes this possible.
Digital Audio Extraction (DAE) is the process of copying audio
from a CD to another medium while keeping the audio in its
original digital state. Also known as "ripping",
most users use DAE techniques to pull tracks (songs) from an audio
CD to a computer's hard drive and then to a recordable CD. Keeping
the song in an all-digital format greatly reduces the chances of
audio discrepancies.
When a CD player/drive plays a Red Book CD (CD audio format)
the drive performs a digital-to-analog conversion in real-time so
the audio can be played through speakers. Before digital audio
extraction, this audio had to be re-recorded and re-digitized if a
user decided to put the song on a recordable CD. This
digital-to-analog-to-digital conversion was very time consuming
and unwanted noise was usually introduced. Depending upon the
quality of the CD-ROM drive, computer hardware, and software,
digital audio extraction can make nearly flawless digital copies
of songs at a fraction of the time.
Copying a song from a Red Book CD is much different than
copying a file from a CD-ROM (the Red Book is discussed later in
this chapter). Songs are stored in tracks on the CD and drives
read these tracks as they spin under the laser assembly. Since the
audio information is "streamed" to the drive, special
digital audio extraction software must be used. This software
reads the raw information of a track as it is streamed and
collects the information into a .WAV file. This .WAV file can then
be played on a computer or copied back to a recordable CD along
with other songs to create a custom audio CD.
When DAE is used to create .WAV files on a computer, they are
uncompressed and can be quite large in size. Other audio formats
such as MP3 and Ogg Vorbis compress these raw files into much
smaller files with minimal loss of song quality.