[sdiy] Craig Anderton's Multiple Identity Filter

David G Dixon dixon at mail.ubc.ca
Fri Oct 28 01:21:18 CEST 2016 

Also, I forgot to mention that the Polaris has some allpass modes, and these
have been further massaged into a poor man's phase shifter.  Quite a lot of
value for 229 bucks! 

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] 
> On Behalf Of David G Dixon
> Sent: Thursday, October 27, 2016 4:12 PM
> To: 'Tom Wiltshire'
> Cc: 'sdiy'
> Subject: Re: [sdiy] Craig Anderton's Multiple Identity Filter
> 
> 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
> > > 
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> > 
> 
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