[sdiy] Experimental VCA RFC

[David G. Dixon]

> I will have to check about WAV file, but I would not trust MY 
> hearing. 

In my experience, it's hard to hear how pure a sine wave is unless you can
compare it to one you know to be virtually pure (like a filtered quadrature
wave).  When I adjust the trimmers on my sine shapers, I can hear the second
and third harmonics getting stronger or weaker on opposite sides of the
"sweet spot", but it's hard to say how "pure" the adjusted sine really is
based on hearing alone.