[sdiy] 2 Pole SVF manipulations

[Magnus Danielson]

Justin,

On 02/27/2013 10:07 PM, Justin Owen wrote:
> http://www.sdiy.org/juz/svf_poles.pdf
>
> Part 1 shows a simplified block/signal-flow diagram of the 2 Pole SVF that so many people have worked on over the years.
>
> I was wondering if anyone could answer (or speculate) what would happen at Outputs A through E for variations 2, 3 and 4 with regards to Filter Type (HP, LP etc), Phase and Attenuation/Slope?
>
> My apologies if that's a vast (or an utterly ridiculous) question!

You make a bit of a mistake here.

In a State Variable Filter, you have an input summer and then a number 
of integrator in series. The feedback terms from the outputs B-E to the 
mixer providing A will essentially be linear proportional to the pole 
polynomial of the transfer function, where as the outputs A-E can form a 
sum proportional to the zero polynomial of the transfer function. This 
is the property of a proper state-variable filter.

State-variable filters is kind of clean in this regard.

With integrators like this, lifting the base more and more, the highest 
output will become the LF response and the A will be the HF response, 
with 6 dB slope, shifts for each stage, as can be expected from the 
integrator stages.

Cheers,
Magnus