[sdiy] Good Expo curve for VCA use..

[Scott Nordlund]

> But note: the attack portion is an exponential charge curve as in your Expo1.
> This sounds good for sounds that start quickly, but is not useful for
> slowly fading in a sound in a constant fading manner.

Actually, I tend to think that the "inverted decay" curve (in analog envelopes it's generally an inverted decay up to a preset threshold, at which point it switches to the decay stage) is more desirable than an exponential attack. An exponential attack (the DX7 being a good example of this) tends to sound unnatural, like a sound played in reverse - definitely not "constant fading". On a DX7 you generally need to use two envelope stages to get a usable attack.