Apple Final Cut Pro 5 - Manual (Page 825)

38 Part I Media and Project Management
Fundamentals of a Sound Wave
The simplest kind of sound wave is a sine wave. Audio sine waves rarely exist in the
natural world, but are a useful place to start because all other sounds can be broken
down into combinations of sine waves. A sine wave clearly demonstrates the three
fundamental characteristics of a sound wave: frequency, amplitude, and phase.
Frequency
Frequency is the rate, or number of times per second, that a sound wave cycles from
positive to negative to positive again. Frequency is measured in cycles per second or
hertz (Hz). Humans have a range of hearing from 20 Hz (low) to 20,000 Hz (high).
Frequencies beyond this range exist, but they are inaudible to humans.
Amplitude
Amplitude (or intensity) refers to the strength of a sound wave, which we interpret as
volume or loudness. People can detect a very wide range of volumes, from the sound
of a pin dropping in a quiet room to a loud rock concert. Because the range of human
hearing is so large, audio meters use a logarithmic scale (decibels) to make the units of
measurement more manageable.
Phase
Phase compares the timing between two similar sound waves. If two periodic sound
waves of the same frequency begin at the same time, the two waves are said to be
in phase. Phase is measured in degrees from 0 to 360, where 0 degrees means both
sounds are exactly in sync (in phase) and 180 degrees means both sounds are exactly
opposite (out of phase). When two sounds that are in phase are added together, the
combination makes an even stronger result. When two sounds that are out of phase
are added together, the opposing air pressures cancel each other out, resulting in little
or no sound. This is known as phase cancellation.
Time
0
–
+
1 ms
Amplitude (dB)