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Digital Audio Fundamentals
Digital audio is a numeric representation of sound; it is sound stored as
numbers. In order to understand what the numbers mean, you need to
start with the basic principles of acoustics, the science of sound.
Basic Acoustics
Sound is produced when molecules in the air are disturbed by some type
of motion produced by a vibrating object. This object, which might be a
guitar string, human vocal cord, or a garbage can, is set into motion
because energy is applied to it. The guitar string is struck by a pick or
Þnger, while the garbage can is hit perhaps by a hammer, but the basic
result is the same: they both begin to vibrate. The rate and amount of
vibration is critical to our perception of the sound. If it is not fast enough
or strong enough, we won't hear it. But if the vibration occurs at least
twenty times a second and the molecules in the air are moved enough,
then we will hear sound.
Example—A Guitar String
To understand the process better, let's take a closer look at a guitar
string.
When a Þnger picks a guitar string, the entire string starts to move back
and forth at a certain rate. This rate is called the frequency of the
vibration. Because a single back and forth motion is called a cycle, we
use a measure of frequency called cycles per second, or cps. This
measure is also known as Hertz, abbreviated Hz. Often the frequency of
vibration of an object is very fast, so we can also express the frequency in
thousands of cycles per second, or kilohertz (abbreviated kHz).
The actual distance the string moves is called its displacement. This is
proportional to how hard the string is plucked. A greater displacement
results in a louder sound.
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