[sdiy] Experimental VCA RFC

[Dave Kendall]

>  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.
>
Seconded. When trimming a sine-wave shaper, it's easy to hear the sweet 
spot, but only by sweeping around it.
Hearing a wave and deciding if it's correct with no reference 
comparison is tricky at best, even with a scope.

cheers,
Dave