Chapter One: An Acoustics Primer
4. What are the characteristics of sound waves? | page 2
Noise is characterized as being aperiodic or having a non-repetitive pattern.
Some periodic waveforms can be complex enough to be perceived as noise if our ears cannot detect perceptible pitches. Many real-world sounds, such as the "chiffy" attack of a flute note contain some combination of periodic and aperiodic components.
For further study, see Hyperphysics->Periodic Motion
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