Apple Logic (1.1) - Manual (Page 90)

90 Chapter A Audio and MIDI Basics
Audio
Audio, as a term, basically refers to any sound that you can hear. In the physical, as
opposed to computer world, this is known as Analog Audio. When Logic records analog
audio signals via an audio interface connected to, or installed in, your computer, the
audio is converted into digital information. This information is stored as a Digital Audio
file on your computer’s hard disk.
As with MIDI, the Digital Audio part sounds technical, but really isn’t. As discussed
earlier, computers talk “digitally”, and need to deal with analog audio signals as digital
information.
Important: Unlike MIDI, digital audio files are actually recordings of sounds, not an
instruction language.
Digital and Analog Recording
While digital audio recording is similar in concept to analog recordings made on tape,
the technical differences are significant. For much of the 20th century and into the 21st,
analog tape recordings have been used for the storage of audio performances—
spoken, sung, and played.
The analog tape medium is a thin plastic strip coated in tiny metal particles. It is usually
stored on a roll or spool, or as a cassette tape, which you’re probably familiar with.
The process of analog tape recording involves the transmission of small electrical
charges, sent to the magnetic “heads” of a tape recorder. Changes to the strength of
these charges alter the magnetic fields generated by the heads, and rearrange the
positions of the metal particles on the tape. Needless to say, this is a less than precise
science. Due to the randomness involved in the rearrangement of magnetic particles
on tape (and other technical reasons), the recordings are said to be “analogous”—
similar to the actual performance.
Digital recording, on the other hand, is much less random. Analog signals are
converted into digital audio signals via the ADC (Analog to Digital Converter) of the
audio interface. The digital audio signal, can be are stored “digitally” on your computer’s
disk—as a series of ones and zeroes. Provided this file remains consistent, digital
recordings will be virtually identical each time they are played back.
In a copying situation—tape to tape—there is no comparison between analog and
digital recordings. Each subsequent copy of an analog recording becomes noisier and
less like the source material. This is the “random” factor of the magnetic particles
becoming less like the original each time a copy is made.
Digital audio files, on the other hand, can be copied any number of times, with each
subsequent copy adding no noise.