FM, Interval / Pulse Width, "Filter"
S: frequency modulation:
A + UP / DOWN = depth higher / lower
A + LEFT / RIGHT = modulation frequency higher / lower
Because frequency distribution is not linear but exponential (semitones) any change
in depth or frequency may cause a totally different sound. Changes of the basic
pitch also modify the sound characteristics. For typical FM-sounds both points
should not go to far out of the lower left corner (high frequency, low depth).
Although usage is a little tricky for this parameter, it offers the widest range of
possible sound variations.
Example: S 3
R: relative pitch of 2 oscillators / pulse width