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

Andrew Simper andy at cytomic.com
Fri Mar 7 10:27:15 CET 2014

Oh and the frequency response plots of all the simultaneous outputs (I
left out the peaking / allpass but you can get that too):



On 7 March 2014 17:25, Andrew Simper <andy at cytomic.com> wrote:
> On 6 March 2014 18:22, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>> Richie wrote:
>>> More likely option 2 if the product has a single global feedback path in
>>> which you can insert an external processor.  The 4-pole SVF is a "leapfrog"
>>> arrangement with multiple feedback paths if I remember correctly.
>> It's horrendous - the maths is taking some time to crunch
>> successfully...not helped by not having much spare time at the
>> moment...
>> Rane have an app note with the design of a 4-pole SVF, and some guy in
>> Finland designed one for his masters thesis.  But in both cases the
>> frequency and damping are fixed.  Turning them into successfully
>> controllable Freq and Q SVFs is a bit more of a challenge :)
> The math isn't so bad, not sure if there are any gotchas in an actual
> circuit realisation, I've only done the theory and simulations thus
> far. You do end up needing two different resonance gains, but they
> don't have to be that exact exact because of the structure. It turns
> out to be pretty much the same as a regular SVF, you need to limit the
> bandpass output in the same way, it is the "dominant" damping term
> that needs to be tamed for self oscillation.
> Here is an audio example of a circuit model of a 4 pole SVF done in
> the same style as a OSCar 2 pole SVF:
> www.cytomic.com/files/svf-4pole.mp3
> Perhaps I should apply for Masters accreditation at that Finish university ;)
> --Andy

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