> Creating a filter slope variable is quite possible. These are the
> commercial modules I know of.

The main question is: do they pan/morph between the 6/12/18/24... dB outputs
of a usual filter design or do they use a filter circuit that has indeed the
filter slope as an additional parameter (I mean if it can generate really
e.g. a 9dB slope, not just mixing a bit the 6dB and 12dB filter stages). I
cannot imagine such a filter based on an analog design, but who knows ...

In any case 'd be very interested if someone knows details about such an
analog filter design.

For bandpasses the situation is a bit different as the slope of a bandpass
is also affected by the resonance: the bandpass peak becomes narrower as the
resonance increases. If the filter design has a constant level at the filter
peak the slope of the bandpass becomes higher as the resonance increases.


Best wishes
Dieter Doepfer