Simple VCA

[jhaible]

> How about this one. Use the CV to control the height of the assymptote
> of the attack phase. Sustain can be simply a ratio of the CV. Therefore
> no need for a VCA or whatever at all. All done at the EG stage. I'm sure
> Oberheim did this with the later OB-Xs using the CEM3310s.

Early OB-8's used the classic (VCA) approach, later revisions used the
variable assymptote method.

JH.