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Physics of perceiving musical pitches

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  • John Deamer
    All singers take note ...or notes. jd PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 436 June 28, 1999 by Phillip F.
    Message 1 of 1 , Dec 31 5:36 PM
      All singers take note ...or notes.

      jd

      PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics
      News Number 436 June 28, 1999 by Phillip F. Schewe and Ben Stein

      PERCEIVING MUSICAL PITCHES may require much less neural processing and
      occur at a lower level of the nervous system than previously thought,
      according to a new explanation, offering possible insights into
      designing better hearing aids. A musical note is defined mainly by its
      lowest pitch, known as its "fundamental frequency," but a note also
      typically contains higher-pitched "overtones" with frequencies that are
      some multiple of the fundamental. Even when the fundamental frequency is
      completely removed from a note, the overtones often allow listeners to
      perceive the missing fundamental anyway. Being able to perceive missing
      frequencies may explain why hearing a classical symphony through a tiny
      radio, which cannot satisfactory reproduce the lowest-frequency pitches,
      sounds reasonably faithful to a live version heard in a concert hall.

      Recent explanations of how we perceive "residue tones" require extensive
      amounts of neural processing, which can only take place in the cerebral
      cortex. However, researchers in Spain and Italy (Julyan Cartwright,
      Higher Council for Scientific Research, Spain, 011-34-958-243360,
      julyan@...) propose that residue perception may result from a
      "nonlinear" process, involving the generation of frequencies that are
      not multiples of the original signal. Much more efficient than previous
      linear models, their proposed mechanism can take place at neural centers
      much earlier than the cerebral cortex. Specifically, they propose a
      "three-frequency resonance" that takes place in some neural processing
      center before the cerebral cortex, in which the electrical signals
      generated by two overtones stimulate a population of nerve cells to fire
      electrical signals at a third frequency different from those of the two
      overtones. Better understanding of pitch perception may lead to
      applications in medicine; it is already known, for example, that hearing
      aids which concentrate on making the fundamental frequencies more
      intelligible produce better results than simple amplification alone.
      (Cartwright et al., Physical Review Letters, 28 June; sound samples at
      http://www.imedea.uib.es/~piro/PitchPage/ )

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