ct.  Possible values
     for x are:
          0 - sine (default)      /\    /\     (2 cycles shown)
          4  (without retrigger)     \/    \/

          1 - ramp down          | \   | \
          5  (without retrigger)     \ |   \ |

          2 - square             ,--,  ,--,
          6  (without retrigger)    '--'  '--'

          3 - random: a random choice of one of the above.
          7  (without retrigger)
     If the waveform is selected "without retrigger", then it will not
     be retriggere