EG design

[Grant Richter]

> 
> BTW, if you consider the stuff about the level increase from above,
> linear or nearly linear truncated RC-type contours only make a very
> little difference. Everything is fine (for natural sounding stuff), as
> long
> as you
> (1) don't have linear decay / release slopes
> (2) don't use an exponential VCA.
> 
Dear Juergen -

I am not following you reasoning here. If you go by textbook acoustic
theory, volume (the psychoacoustic perception of amplitude) is perceived
exponentially. Just as pitch (the psychoacoustic perception of frequency)
is perceived exponentially. I can prove this to my satisfaction by feeding
a manually adjustable linear control voltage to a linear VCA. All volume
change is bunched up at the top end and the first 70% of control travel has
no apparent response. If I switch the VCA to exponential response, then the
control action is spread out over the whole control travel.

In the case of the exponentially charging/discharging envelope into a
linear VCA, the exponential curve is supplied by the envelope rather than
the VCA. With the caveat that the attack portion is an inverted exponential
response. This sound just fine, lots of Minimoog owners will tell you so!
:)

In the case of a linear envelope (which is a more generally useful
controller for all parameters) the exponentiation need to be supplied by
the VCA. The later synthesizer designers i.e. Serge thought the best
solution was to make psychoacoustic parameter "fixing" at the module
inputs. The idea being that all parameters respond "linearly" to the same
controller curve.

You can simulate both exponential and inverse exponential envelopes from a
linear EV by feeding the rate control input with either positive or
negative polarity from the output. The Wiard envelator has this patch
normalized to the rate control inputs. All you have to do to simulate a
Moog EV is turn up the modulator inputs.

I don't want to be dogmatic - if it sounds good, throw out the book. For my
$0.02, I say the voltage controlled linear envelope is the most general
solution as a controller.

Grant Richter
Wiard Synthesizer Company
http://www.wiard.com/