Objects that vibrate in a randomised fashion produce sounds that we describe as noisy. This is because the sounds produced contain a random assortment of frequencies.
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A term that describes sounds that have a diffuse spread of spectral energy. It is often contrasted with pitched sounds. Noisy sounds may be hard to define in terms of pitch because their spectral energy covers a wide range of frequencies and is not concentrated, but diffuse.
White Noise
This sound file plays white noise (careful, it might be very loud!)
This image shows the complete spread of sound energy across the spectrum.
