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

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Mon Jan 5 14:50:15 CET 2015


Hi Andy,

Thanks for sharing this interesting work.

In the discretization technical paper it would have been interesting to 
see the resulting z-domain frequency responses for the digital 
realisations of the filters, so that comparisons can be made with the 
original s-domain analogue prototypes as the cutoff frequency approaches 
the Nyquist limit.  (The s-domain frequency responses are "textbook" 
analogue 2nd order shapes, so aren't particularly interesting by 
themselves.)

-Richie,

PS. The mixture of "electrical schematic" and "signal flow" 
representations in the same diagrams might be a little confusing to 
some.  I'm an electronics engineer so am familiar with looking at both, 
but they usually aren't mixed in the same diagram.





On 2015-01-05 13:25, Andrew Simper wrote:
> 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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