A waveform that continuously repeats itself and 
  we as humans can perceive (or tell) the repetition as pitch. 
Oscillators are used to create periodic waveforms 
  whose shapes include sine, square, 
  triangle, rectangular, 
  and ramp. 
  The opposite of periodic waveforms are noise 
  waveforms.
 
 
  
  Click the image to hear an example of a periodic waveform.
© C.Chris Peters 2010