[sdiy] Sallen Key with input mixing to generate all shapes

[Andrew Simper]

Sam you're a legend!

You just saved me an IEEE membership just to look at one paper and
some pain in "fixing" the schematics in it. I was really interested in
the SVF with mixing inputs and you just delivered it straight to me
with a wonderfully clear LTSpice schematic, thank-you!

I hope I can come up with some more interesting designs to help
contribute to the synth community like you are doing.

The positive feedback path around the Band section and that you noted
is from the ARP 4023, it looks like the OSCar also copied this idea -
thanks for pointing out the original.

Andy

-- cytomic -- sound music software --


On 23 December 2014 at 09:34,  <houshu at muj.biglobe.ne.jp> wrote:
> Hello list,
>
> Input mixing structure is possible with state-variable-like filter.
>
> http://houshu.at.webry.info/201202/article_1.html
>
> HPF response is 12dB/oct not 6dB/oct. Multiple functions with
> beautiful frequency response can be obtained from this very
> simple circuit.
>
> Basic structure is like ARP4023, which can be derived from
> ordinary state variable filter:
> http://houshu.at.webry.info/200602/article_1.html
>
> I built a module with satisfactory results:
> http://houshu.at.webry.info/201202/article_2.html
> http://houshu.at.webry.info/201411/img22_1.141731631693745480177.html
> Power consumption is as small as 5mA.
>
> I designed it for single supply operation.
> Bipolar supply operation is possible by changing the
> exponential converter (Untested):
> http://www5b.biglobe.ne.jp/~houshu/synth/VcSvf01a.gif
>
> Sam HOSHUYAMA
> Saitama, Japan
>
> ----- Original Message -----
> From: "Andrew Simper" <andy at cytomic.com>
> To: "synthdiy diy" <synth-diy at dropmix.xs4all.nl>
> Sent: Sunday, December 21, 2014 16:54:23
> Subject: [sdiy] Sallen Key with input mixing to generate all shapes
>
> Hey guys,
>
> I've noticed many Sallen Key synth filters can generate different
> responses by sticking the input into various points of the circuit,
> but they only ever deliver a 1 pole high pass, and a very weak notch.
> I've worked out the theory for generating all the same responses as
> you can get by mixing the outputs of an State Variable, but instead
> mixing the inputs to a Sallen Key. I've put together a technical paper
> on it here:
>
> https://cytomic.com/files/dsp/SkfLinearTrapezoidalSin.pdf
>
> and I've sketched the basic structure of what is going on here (taking
> an MS20 v2 type OTA Sallen Key as the basis):
>
> www.cytomic.com/files/dsp/SkfInputMixing.jpg
>
> the important voltages are:
>
> vamp1 = (m0*v0) - (m1*v0 + v1)
> vamp2 = (m1*v0 + v1) - (v2)
> vcap1 = (v1) - (res*v2 + m2*(-v0))
> vcap2 = (v2) - (m2*v0)
>
> where m0 = low mix, m1 = band mix and m2 = high mix
>
> Also for those interested in a digital implementation I've also
> included in the paper is also a trapezoidal integrated linear circuit
> model use state space increments and high precision coefficient
> calculation.
>
> Andy
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