rand lo hi

Generates a single random value in uniform distribution from lo to
hi.  It generates this when the SynthDef first starts playing, and
remains fixed for the duration of the synth's existence.

> f <- rand 200 1200
> l <- rand (-1) 1
> let e = line KR 0.2 0 0.1 RemoveSynth
>     o = fSinOsc AR f 0
> audition (out 0 (pan2 (o * e) l 1))