Doepfer

For a bandpass filter, wouldn't a lowpass and highpass in series be  
ideal? On the other hand I've been thinking about a variation on the  
classic diode ladder design:
4 6db lowpass normalled in series and with a main frequency control  
for all four as well as individual frequency potentiometers. There  
would only be two freq cv inputs: all and spread

As well as individual outputs one could provide a mix out with  
polarizers for every stage.

This configuration would allow for every possible filter type and  
slope including tb-303 emulation, by tuning stage 4 one octave above  
the rest. What would be really cool is if it would have morphing  
capabilities like the a-107 (I think, don't remember the numbers by  
heart). But this filter would be superior (custom types, slopes, no  
switching clicks etc)

Cheers

26 apr 2010 kl. 10.09 skrev <yahoo@doepfer.de>:

> > 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
>
> 


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