[sdiy] Craig Anderton's Multiple Identity Filter

[David G Dixon]

Yes, those are what the Polaris outputs look like as well.  In the highpass
output, the signal doesn't really change at all above about log w = 0.25 at
any resonance setting.  In any case, the filter sounds good.

My Korgasmatron II filter uses switched inputs to get multimodes from MS-20
topology filters.  The beauty of that technique is that different signals
can be sent through the same filter with different modes.  In other words,
you can have one signal filtered at 12dB lowpass, and another filtered at
12dB highpass, through the same circuit at the same time.  It's kinda cool.
Here's that one: https://intellijel.com/eurorack-modules/korgasmatron-ii/

> -----Original Message-----
> From: Andrew Simper [mailto:andy at cytomic.com] 
> Sent: Wednesday, October 26, 2016 8:09 PM
> To: David G Dixon
> Cc: KA4HJH; sdiy
> Subject: Re: [sdiy] Craig Anderton's Multiple Identity Filter
> 
> PS: here is an example of the difference between the band 
> pass responses for the Xpander summed outputs vs switching 
> the input to make two high pass filters and two low pass filters:
> 
> http://www.cytomic.com/files/dsp/cascade-bandpass-sum-vs-switch.png
> 
> And here is the difference between the high pass responses:
> 
> http://www.cytomic.com/files/dsp/cascade-highpass-sum-vs-switch.png
> 
> Note that the high pass with switching the input is a mirror 
> image of the classic low pass moog response: the resonance 
> peak sweeps downwards with increasing resonance, and the pass 
> band drop is in the upper frequencies. The Xpander summed 
> output version is a bit weird looking, but hey, this is music 
> and weird is good too!
> 
> Andy
> 
> On 27 October 2016 at 09:57, Andrew Simper <andy at cytomic.com> wrote:
> > Hi David,
> >
> > As far as I remember the Oberheim Matrix only had a fixed 4 pole 
> > cascade type low pass filter, did you mean the Oberheim 
> Xpander? If so 
> > then yes this is the easier way to generate different responses by 
> > taking weighted sums of the output of each stage, but you don't get 
> > the "correct" responeses, you get sags above the cutoff in the band 
> > pass and high pass modes, and amplitude attenuation below 
> cutoff with 
> > changing resonance in all modes, which kind of sounds like changing 
> > the cutoff upwards with increasing resonance in band pass and high 
> > pass modes, but the resonant peak stays put.
> >
> > Cheers,
> >
> > Andrew
> >
> > On 27 October 2016 at 03:23, 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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> >>> Synth-diy at dropmix.xs4all.nl
> >>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >>
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