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

Andrew Simper andy at cytomic.com
Mon Jan 5 14:25:37 CET 2015


I've taken Sam's ARP transposed SVF design with input mixing and
written a discretization technical paper on it. I've also updated the
SKF (Sallen Key Filter) design I did with input mixing to more
explicitly address using different input signals.

Idealized circuit diagrams:
http://cytomic.com/files/dsp/SkfInputMixing.jpg
http://cytomic.com/files/dsp/SvfInputMixing.jpg

Technical papers:
http://cytomic.com/files/dsp/SkfInputMixing.pdf
http://cytomic.com/files/dsp/SvfInputMixing.pdf

All the best,

Andrew Simper
-- cytomic -- sound music software --


On 24 December 2014 at 23:44,  <houshu at muj.biglobe.ne.jp> wrote:
> Hello Andy and list,
>
> I'm grad you like my schematics.
>
> Multiple point signal injection is a very interesting idea.
> I guess you can get any response from famous filter structure
> keeping the original sound.  Four pole filter such as ladder
> filter may be a good target.
>
> Sam HOSHUYAMA
> Saitama, JAPAN
>
>
>
> ----- Original Message -----
> From: "Andrew Simper" <andy at cytomic.com>
> To: houshu at muj.biglobe.ne.jp
> Cc: "synthdiy diy" <synth-diy at dropmix.xs4all.nl>
> Sent: Tuesday, December 23, 2014 13:00:39
> Subject: Re: [sdiy] Sallen Key with input mixing to generate all shapes
>
> 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
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy



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