has
the golden mean as a solution.  In the second case,
x^3 = 2*x + 1 also has the golden mean as a solution.
Sadly, this sequence does not continue.  The golden
mean is obviously not unique in this regard; 
if our ratio is 2+sqrt(3) then the wrap-around
fourth sideband is the ratio squared.  A table of
Pisot numbers gives many more such numbers.

1+sqrt(2) squared = 1 + 2* same

-->

<!-- PM producing a frequency shift:
(with-sound ()
  (let ((o (make-oscil 200.0))
        (e (make-env '(0 0 1 1) :scaler 3