[sdiy] Craig Anderton's Multiple Identity Filter

[David G Dixon]

Exactly.  There are 28 really useful modes, and I believe that 23 of them
survived into the Polaris.

The first input (the feedback) only requires one resistor -- on or off at
unity gain -- so that one is done with a DG418.  The four outputs require 5
to 8 resistors for all the different gain factors, and this is done with
DG408.  The fourth bit is for the Enable pin, which allows one to select no
input from that source.  It's pretty damn elegant, and was a lot of fun to
design.  There's also a switchable asymmetric distortion circuit on the
multimode output which sounds really good, plus the inputs can be overdriven
above unity gain.


> -----Original Message-----
> From: Tom Wiltshire [mailto:tom at electricdruid.net] 
> Sent: Thursday, October 27, 2016 4:34 AM
> To: David G Dixon
> Cc: 'KA4HJH'; 'sdiy'
> Subject: Re: [sdiy] Craig Anderton's Multiple Identity Filter
> 
> 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"
> >> 
> >> _______________________________________________
> >> Synth-diy mailing list
> >> Synth-diy at dropmix.xs4all.nl
> >> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> > 
> > _______________________________________________
> > Synth-diy mailing list
> > Synth-diy at dropmix.xs4all.nl
> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>