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

Tue Jan 6 02:52:17 CET 2015

Richie, do these look better?

http://cytomic.com/files/dsp/SvfInputMixing2.jpg
http://cytomic.com/files/dsp/SkfInputMixing2.jpg

Andy
-- cytomic -- sound music software --

On 6 January 2015 at 09:28, Andrew Simper <andy at cytomic.com> wrote:
> On 5 January 2015 at 21:50, <rburnett at richieburnett.co.uk> wrote:
>>
>> Hi Andy,
>>
>> Thanks for sharing this interesting work.
>
> Your welcome!
>
>
>> 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,
>
> It is trapezoidal integration, which gives a cramped response which is
> equivalent to the bi-linear z transform which is why I didn't bother.
> Please read the other papers I wrote for derivations and plotting of
> the z-domain transfer function. I show the derivation of forming the
> z-domain transfer function directly from trapezoidal integration here:
> http://cytomic.com/files/dsp/SvfLinearTrapOptimised2.pdf in the
> section "Transfer functions for low, band, high, notch, and peak,
> continuous and discrete"
>
>
>> 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.
>
> I originally had little triangle amp blocks but things looked messy.
> Donald posted a link to this paper:
> http://www.ka-electronics.com/images/pdf/Steiner_Filter.pdf , which
> uses a square with a sigma sign in the middle to show a summing block,
> so I used this idea but instead used a more modern + sign in a circle.
> Should I switch it to how Steiner does it with a square and sigma? Is
> that more standard for idealised circuit diagrams? I show the
> development of the notation I used here:
> http://cytomic.com/files/dsp/OnePoleLinearLowPass.pdf with the full
> resistor divider network to use a circle with a + instead, but I am
> happy to change it if there is something just as succinct and more
> standard.
>
> All the best,
>
> Andy
>
>
>>
>>
>>
>>
>>
>>
>> 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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