[sdiy] Good 24db/oct HP-LP-BP-Notch filter Schematics ??

Andrew Simper andy at cytomic.com
Thu Mar 6 14:22:23 CET 2014

On 6 March 2014 18:00, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 6 Mar 2014, at 06:34, Andrew Simper <andy at cytomic.com> wrote:
>> On 6 March 2014 02:40,  <blacet at blacet.com> wrote:
>>> As far as I know, the state variable filter design is the only one that
>>> has simultaneous outputs as you require. This is a 12dB design with two
>>> stages, although with enough feedback/Q, the apparent slope is much
>>> greater.
>> You can make 4 pole SVFs that contain 4 integrator stages and produce
>> H4 L4 H1L3 H2L2 H3L1, and you can then sum and difference H4 and L4 to
>> create allpass and notch.
> Do you have any references for that, Andrew? I'd like to see how that's done. I've tried searches for "4-pole SVF" but can't find much.

There is plenty of material, mostly in speaker crossover design. You
need to search for "4th order state variable filter", not "4-pole

> In summary then, the RS110 is either:
> 1) A 4-pole SVF design
> 2) A 4-pole LPF with pole-mixing providing simultaneous outputs
> Thanks,
> Tom

Because of the single resonance send / return I believe these to be
the most likely two candidates since they take the fewest parts. If
anyone has one it should be easy to listen to which it is, if the
resonance output sounds the same as the bandpass output then it is
option 1), if it sounds like the low pass output it is option 2).
Another way to check is to adjust the resonance gain externally (ie
not using the resonance knob), and see if the passband gain decreases,
then it would be option 2).


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