Tracker 4.42

### 4 Vibrato

phi is the speed of the vibrato and plow the depth of the vibrato. Null values for phi or plow just mean `keep the previous value.'
The basic vibrato waveform is a sine waveform. It can be changed to a square waveform, or a rampdown waveform.

Here are the actual shapes used, with origin et all.

          ****                     ********                     **
        **    **                                              **
       *        *                                           **
      *          *                                        **
                  *        *                                          **
                   **    **                                         **
                     ****                  *******                **

         Sine 0                     Square 1                Rampdown 2

(see Set vibrato waveform, for a detailled discussion of some aspects of that effect).

The resulting waveform has an amplitude of 2*depth, e.g., its values are in the range [-2*depth, 2*depth], and its full period is 64/speed ticks.

The position in the waveform is reset at each and every new note on the channel.

Scrolling mode:

      	1 A-4 vb 5/3

sample number / note / depth/speed.