Reference Guide

775
Digital audio fundamentals
Editing audio
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.
The displacement of the string changes as the string vibrates, as shown here:
The segment marked “A” represents the string as it is pulled back by the pick; “B” shows it moving
back towards its resting point, “C” represents the string moving through the resting point and onward
to its outer limit; then “D” has it moving back towards the point of rest. This pattern repeats
continuously until the friction of the molecules in the air gradually slows the string to a stop. As the
string vibrates, it causes the molecules of air around it to vibrate as well. The vibrations are passed
along through the air as sound waves. When the vibrations enter your ear, they make your eardrum
vibrate, and you hear a sound. Likewise, if the vibrating air hits a microphone, it causes the
microphone to vibrate and send out electrical signals.
In order for us humans to hear the sound, the frequency of the vibration must be at least 20 Hz. The
highest frequency sound we can hear is theoretically 20 kHz, but, in reality, it's probably closer to 15
or 17 kHz. Other animals, and microphones, have different hearing ranges.
If the simple back-and-forth motion of the string was the only phenomenon involved in creating a
sound, then all stringed instruments would probably sound much the same. We know this is not true,
of course; the laws of physics are not quite so simple. In fact, the string vibrates not only at its entire
length, but at one-half its length, one-third, one-fourth, one-fifth, and so on. These additional
vibrations (overtones) occur at a rate faster than the rate of the original vibration (the fundamental
frequency), but are usually weaker in strength. Our ear doesn't hear each frequency of vibration
individually, however. If it if did, we would hear a multinote chord every time a single string were
played. Rather, all these vibrations are added together to form a complex or composite sound that
our ear perceives as a single tone.