CAKEWALK SONAR User Manual page 319

The waveform of a trumpet blast might look like this:
And the waveform of a spoken word might look like this:
The three waveforms shown above are quite different from one another, both in appearance and sound.
Each has its own characteristic shape, or envelope, and each has its own complex combination of
frequency components, which can change across the duration of the sound.
The center line of a waveform is the zero line; it corresponds to the rest position (displacement of 0) of
the original vibrating object. (A waveform for perfect silence would be a horizontal line at zero.) Back
and forth motions of the vibrating object translate to upward (positive) and downward (negative)
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