[sdiy] Craig Anderton's Multiple Identity Filter

[Tom Wiltshire]

Hi David,

That must share quite a few similarities with Olivier's Four Pole Mission filter (previously mentioned, link below). The great thing about doing this type of pole-mixing with the 2164 is that the filter stage (VCA+integrator) is inverting and provides a low impedance output, so there's no need for buffering or inverters, which the original Matrix-12/Xpander filter design (based on the CEM3372) is covered in. That makes for a very neat and clean design.

Olivier's design follows the Xpander pretty closely and uses the same technique of switching the filter cap of the first stage to make it into a buffer, but with a 2164-based design you can equally well provide a input to the mixer from the input mixer and avoid this.
I'm guessing you went this way. A 17-bit code gives you at least 8 resistor options for each of 5 inputs to the mixer (e.g. a 4051 for each one). Under uP control this gives fantastic flexibility and the problem becomes finding "useful" or "interesting" responses from a system which will include many duplicates and things that just aren't that good - including 30 from the 131,000+ possibilities suggests you did the required serious pruning!

Tom

http://mutable-instruments.net/shruthi1/build/4pm


On 26 Oct 2016, at 20:23, David G Dixon <dixon at mail.ubc.ca> wrote:

> I've got a filter design called the "Polaris" that gives nearly 30 different
> useful filter modes in a much simpler say than the MIF, and doesn't need a
> Curtis chip to do it.  Intellijel sells it for $229.  If you want to check
> it out, go here: https://intellijel.com/eurorack-modules/polaris/  It's
> based on a Roland-esque cascaded-stage four-pole filter, and takes
> inspiration from Grant Richter's old Oberheim Matrix multimode filter
> design, but it goes a fair bit further than that.  The mode switching is
> done with a microcontroller generating a 17-bit code which controls five
> analog switches, which I still don't know how to do, so I don't have a
> handmade version of it yet.
> 
>> -----Original Message-----
>> From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] 
>> On Behalf Of KA4HJH
>> Sent: Wednesday, October 26, 2016 8:55 AM
>> To: sdiy
>> Subject: Re: [sdiy] Craig Anderton's Multiple Identity Filter
>> 
>>> On Oct 26, 2016, at 4:37 AM, Andrew Simper <andy at cytomic.com> wrote:
>>> 
>>> From what I can see with Craig Anderton's filter it won't actually 
>>> give the "correct" responses for all the different filter 
>> types unless 
>>> there is a way to switch the polarity of the resonance, and 
>> also where 
>>> the resonance is added. Am I missing something? Sorry if 
>> I've posted 
>>> all this stuff before.
>> 
>> This is one of the reasons I reposted the link. I remember 
>> some discussion about this and wondered how Craig's design compared.
>> 
>> 
>>> On Oct 26, 2016, at 12:30 AM, Doug Terrebonne 
>> <dougt55 at yahoo.com> wrote:
>>> 
>>> The MIF article has been on synthdiy.com for a long time - 
>>> http://www.synthdiy.com/files/2002/MIF.pdf
>> 
>> I didn't even know it was there.
>> 
>> 
>>> On Oct 26, 2016, at 5:43 AM, Roman Sowa <modular at go2.pl> wrote:
>>> 
>>> Why use predatory file hosting sites while there are sites 
>> like synthdiy.com or synth.net, which AFAIK are managed by 
>> this list members.
>> 
>> I completely forgot they existed but then this is the first 
>> time I've received a complaint about Mediafire.
>> 
>> 
>>> On Oct 26, 2016, at 5:43 AM, Roman Sowa <modular at go2.pl> wrote:
>>> 
>>> Why use predatory file hosting sites while there are sites 
>> like synthdiy.com or synth.net, which AFAIK are managed by 
>> this list members.
>>> 
>>> If anyone's interested I can also host any doc files (no 
>> audio/video/warez or any pirated stuff) at regular downolad 
>> links, no ads, no download buttons or popups.
>> 
>> 
>> Good to know. I may take you up on it.
>> 
>> 
>> Terry Bowman, KA4HJH
>> "The Mac Doctor"
>> 
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