#background_noise__ground_noise  extraneous noise contaminating sound measurements that cannot be separated from the desired signal
  supertype:  #background_signal__background  extraneous signals that can be confused with the phenomenon to be observed or measured; "they got a bad connection and could hardly hear one another over the background signals"
  subtype:  #surface_noise__surfacenoise  noise produced by the friction of the stylus of a record player moving over the rotating record

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