[sdiy] Craig Anderton's Multiple Identity Filter

[Andrew Simper]

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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>>
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