  PowerSpectrumDemo, Version 1.1

  Digital signal generator (sumulator) with power spectrum
  display and sliders for "real time" control, useful for teaching and 
  demonstrating the power spectra of different types of signals and the 
  effect of signal duration and sampling rate. The signal slider selects  
  from 10 different signals (you can change these in RedrawSpectrum.m).
  The Time slider controls the total duration of signal, the Rate  
  slider controls the sample rate, and the F1 and F2 sliders control
  the global variables f1 and f2 which are used in different ways in 
  the different signals.  The Sound slider has only two settings:
  OFF (down) and ON (up).  When Sound is ON, each time a slider is moved,
  the signal (y) is sent to the Windows WAVE audio device. When Sound
  is OFF, no sound is played whena slider is moved. However, even
  when Sound is OFF, clicking on the Sound slider plays the signal 
  once for each click.

  T. C. O'Haver (toh@umd.edu),  version 1.1, May, 2007