Adobe AUDITION 1.5 - Manual (Page 281)

273 ADOBE AUDITION 1.5
User Guide
An audio file on your hard drive, such as a WAV file, consists of a small header indicating
sample rate and bit depth, and then a long series of numbers, one for each sample. These
files can be very large. For example, at 44,100 samples per second and 16 bits per sample,
a file includes 705,600 bits per second. This equals 86 kilobytes per second and more than
5 megabytes per minute. Stereo sound has two channels, so CD-quality sound requires a
little more than 10 megabytes per minute.
Introducing MIDI
In contrast to a digital audio file, a MIDI file might be as small as 10 kilobytes per minute,
so you can store up to one hundred minutes of MIDI per megabyte. MIDI and digital
audio are fundamentally different: digital audio is a digital representation of a sound wave,
MIDI is a language of instructions for musical instruments. A digital audio file seeks to
exactly represent an audio event just like a tape recorder, whether it's a musical perfor-
mance, a person talking, or any other sound. MIDI, on the other hand, is more like sheet
music. It acts as instructions for the re-creation of a musical selection. These MIDI
instructions, however, cannot reproduce highly complex sounds, such as the human voice.
MIDI files record information such as the note to be played, the instrument to play the
note on, the pan and volume of that particular note, and so on. When a MIDI file is played
back, the sound card takes this information and uses its synthesizer to re-create the note
on the right instrument. Because every synthesizer sounds different, the MIDI file will
sound different when played through different sound cards. MIDI support in Adobe
Audition is limited to playback of MIDI files.
Conclusion
To summarize, the process of sampling or digitizing audio starts with a pressure wave in
the air. A microphone converts this pressure wave into voltage variations. An analog-to-
digital converter, found in devices such as sound cards, samples the signal at the sample
rate and bit depth you choose. Once the sound has been transformed into digital infor-
mation, Adobe Audition can record, edit, process, mix, and save your digital audio files.
The possibilities for manipulation of digital audio within Adobe Audition are limited only
by your imagination.
ug.book Page 273 Tuesday, March 16, 2004 1:29 PM