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  1. Noise in which the acoustic energy is distributed over a relatively wide range of frequencies. The spectrum is generally smooth and continuous, although it may vary significantly from "flat." If the broad-band sound does not contain any significant discrete tones, the sound will lack a subjective quality of pitch or tonality.
  2. Spectrum consisting of a large number of frequency components, none of which is individually dominant. Source: http://www.owenscorning.com/around/sound/glossary.asp