What Makes an Envelope Snappy

Florian posted the following to AH. I thought it was probably the most detailed explanation I've come across on what makes an envelope snappy. I asked him if it would be ok to put it up here for others and the archives, and he gave the thumbs up. He also mentioned that the following is basically a short resume from some chapters of his book "Synthesizer." You can find it on amazon. Unfortunately for those of us who do not speak German, it is in German only. I wonder if there's pictures. : )

What Makes an Envelope Snappy:
"There are several aspects:
1.) Speed, shape, of envelope
2.) envelope amount and offset value destination of destination
parameter, sustainlevel (in case of ADSR),
3.) characteristics of modulation,
4.) synchronisation with waveform.

First aspect:
In analogue envelopes (created by loading unloading a capacitor) speed
and shape are related to each other. If whe look at decay, the same
decay value at the beginning of the decayphase causes a much faster
change than at the end of the decay phase, because of the exponential
unloading characteristics of the capacitor.

Second aspect (All values in the following examples from
0=shortest/lowest to 100=longest/highest):
If we now modulate a filte with such an envelope like A=0, D=10, S=0,
R=0. If the cutoff frequency is already at 500Hz), and the envelope
amount is very high - lets say 5 octaves. THis will cause the filter to
open up to 16000 Hz and back to 500 Hz. The most noticable change will
happen between 2000Hz and 500Hz, all above is simply "bright". So all
the fast part of the exponential envelope will happen whil you don't
realize it. And only the slow end of the decay curve will cause a
noticable change. So even if your envelope in general is "fast like
hell", you will destroy this, by wrong modulation settings on the
destination.

Third aspect:
Next question is: how does the destination react on the envelope. A good
example are VCAs, which are available with linear and exponential
characteristics. Our loudness recognition is basically logarithmic. So
We need exponential controls for volume. Since analogue envelopes
already have exponential characteritics, you can use a linear VCA, which
translates the exponential change of the envelope direct to the signals
amplitude change. But for linear changing LFO waveforms you need a
exponentiator, which translates the linear changing waveform to a
exponentially changing waveform and then modulates the amplitude.
Now: If you use a exponential VCA for envelope modulation, you will have
a double exponential function, which will increase the "snappyness" of
the envelopemodulation (but will increase also the effect, which is
described in the second aspect).

Fourth aspect:
Whether a envelope is felt as snappy or has a click in the beginning,
depends also very much on the synchronisation with the waveform of the
VCO(s). Especially if the VCOs tend to eliminate by interference its
often a good idea to patch the gate to the Hardsync in, which causes the
VCO to start at each keypress at a dedicated point of the waveform.


Florian"