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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 finger, 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 finger 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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