nyquist theorem

1 definition found

nyquist theorem - Free On-line Dictionary of Computing (26 May 2007) :

  Nyquist Theorem
  
     <communications> A theorem stating that when an analogue
     waveform is digitised, only the frequencies in the waveform
     below half the sampling frequency will be recorded.  In
     order to reconstruct (interpolate) a signal from a sequence of
     samples, sufficient samples must be recorded to capture the
     peaks and troughs of the original waveform.  If a waveform is
     sampled at less than twice its frequency the reconstructed
     waveform will effectively contribute only noise.  This
     phenomenon is called "aliasing" (the high frequencies are
     "under an alias").
  
     This is why the best digital audio is sampled at 44,000 Hz -
     twice the average upper limit of human hearing.
  
     The Nyquist Theorem is not specific to digitised signals
     (represented by discrete amplitude levels) but applies to any
     sampled signal (represented by discrete time values), not just
     sound.
  
     Nyquist (http://geocities.com/bioelectrochemistry/nyquist.htm)
     
     (the man, somewhat inaccurate).
  
     (2003-10-21)