Meanwhile, a funny little discovery for me was found in the P6 manual. I did a quick skim just now but can't find the bit I'm thinking of, but basically it suggests using the Filter Env in the Poly Mod section in negative mode. This allows for greater range of subtle filter tracking. Or something like that!
I think it's the bit on PP23-24. I 'll quote it here (claiming Fair Use")!
"Changing the Filter Envelope’s Response Curve
By default, the envelopes of all synthesizers are designed to have certain
type of response curve that is largely dependent on the preference of the
designer. In most cases, this can’t be changed. The current preference is
that the faster or snappier the envelopes, the better.
However, in the case of the Prophet-6, there is a hidden feature in the
Poly Mod section that allows you to modify the responsiveness of the
Filter Envelope’s ADSR controls. This opens up a new level of fine
adjustment of these controls that is subtle but powerful. Try it and see.
24 Amplifier Envelope Dave Smith Instruments
To adjust the responsiveness of the filter envelope:
1. Select a program — such as a synth brass sound — that has a slightly
soft but bright attack.
2. Repeatedly play a series of notes or chords on the keyboard, so you can
hear the effect of the adjustments as you follow the steps below.
3. In the Poly Mod section, enable the lp filter as the only destination
(disable all other Poly Mod destinations such as freq 1, freq 2 etc.).
4. In the Poly Mod section, turn the filter env control slightly counterclockwise.
Try a setting of about 11 o’clock.
5. Continue to play a series of chords and turn the env amount knob
clockwise in the low-pass filter section. Try moving it back and forth
between 1 o’clock and 3 o’clock.
6. As you do this, compare different settings of the Poly Mod filter env
control, the Low-Pass Filter env amount, and different Attack, Decay,
Sustain, and Release settings on the Filter Envelope.
The interaction of these controls is worth exploring for greater flexibility
and control of the Filter Envelope.
Amplifier Envelope"