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

[Mattias Rickardsson]

On 6 March 2014 11:22, Neil Johnson <neil.johnson71 at gmail.com> 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 :)

Is the schematic of your 3-pole SVF available perhaps, as a
comparison? The link is broken. :-)
http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=0&subsubmenu=1

A 2-pole SVF starts with removing the LPF output from the input signal
to make the HPF signal (i.e., the signal in the LPF passband is
dampened a lot) which is then integrated 2 times to make the LPF
output. This dampening + signal recovery in the integrators degrades
the signal and gives increased noise already in the 2-pole version,
and I'd suspect a 4-pole SVF would have considerably worse LPF signal
quality after doing this trick twice as much. Any opinions or
experiences?

/mr