It looks like the Cwejman filter (and also the Serge I think) fits the bill.

What is the difference between "bandwidth" and "slope" in the context of
bandpass They would seem to be two ways of describing the variation in one
parameter. But can you actually create a "plateau" in the middle of the
frequency response curve while maintaining the same rate of drop at the
edges

On Fri, Apr 23, 2010 at 4:44 AM, zaum < zaum@... > wrote:

>
>
> > Is it possible to make an analog filter where you can continuously
> > vary the cutoff slope I am imagining a bandpass effect where the
> > band gets continuously narrower and wider. Perhaps a voice is
> > filtered through, at first it sounds human but you continuously dampen
> > off all harmonics until it sounds like a sine wave.
>
> You'd have to continuously determine the pitch to control the
> filter's frequency cutoff and my filter knowledge no real world
> filter would be steep enough to isolate just the fundamental and
> eliminate other frequencies of a human voice once you have the
> determine frequency of it.
>
> Creating a filter slope variable is quite possible. These are the
> commercial modules I know of.
>
> The Serge Voltage Controlled Slope Filter (VCFS) has multimode
> outputs. There seems to be some question if it varies from 6 to 12db.
> I've been told it's done by manipulating the CV's/currents that
> control the two ( ) filter stages but the person mentioning it didn't
> fully understand how it worked. I've not tried one. Certainly not a
> steep slope but supposedly dramatic enough especially when resonating
> (needs to be manually patched since there is no built in loop)
>
> For bandpass and in Euro there is the Cwejman VCEQ-3, which is a
> voltage controlled 3 band parametric equalizer. Am I correct a
> parametric does offer a change in slope rather than merely bandwidth
> Comparing it to a parametric equalizer is probably a better starting
> point than to a VCF. You have a switchable 16db boost or cut (not
> equal to 16 db per octave slope). You can control all the parameters
> (frequency, bandwidth, level) except the boot/cut switch via CV, very
> much unlike a studio parametric that can't be modulated. What totally
> gets me frustrated is Cwejman gives you just one mono in going to the
> 3 filters in series and a mono out of the last one. While the module
> would need to be made wider for 6 more inputs it's simply frustrating
> each band doesn't have it's own in and an out on an expensive module
> like this. I'd love to have a mod that gave them their own ins and
> outs, but it's made more complicated since Cwejman use SMT.
>
> nick
>
>


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