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== Donald Tillman's filter taxonomy<ref>Moved from [[User:Diydsp|Diydsp]]'s [https://sdiy.info/w/index.php?title=Voltage_controlled_filter&oldid=17307 revision as of 11:59, 27 August 2019]</ref> ==
▲== Filter architectures (sorry this is crudely laid out, 1st step was capture info, 2nd pass will organize) ==
Consider a description of a filter as a sort of "taxonomy" with three layers:
* '''Top Layer''': the filter spec, number of poles, response
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* '''Top Layer''': 2 pole, multi-mode
* '''Middle Layer''': 2 integrators and an inverter, in a loop
* '''Bottom Layer''': the circuit, perhaps OTAs<ref
==== Moog ladder ====
The [[Moog ladder filter]] is like that Zen Koan that all students of the
synthesizer electronics temple meditate upon.
"Oren Leavit"<ref name="aamf">[https://synth-diy.org/pipermail/synth-diy/2019-August/171529.html Article "Analyzing the Moog Filter"], Synth-diy mailing list, August 2019</ref>
<nowiki>https://www.allaboutcircuits.com/technical-articles/analyzing-the-moog-filter/</nowiki>
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ladder filter variations: http://www.till.com/blog/archives/2005/03/ladder_filter_v.html
==== Roland MS20 ====
==== Ian Fritz threeler ====
==== Mutant vactrol ====
3-pole, 4-pole, etc - without cascading 2-pole SVFs.
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constants.<ref name="aamf"/>
==== Steiner Parker ====
The Steiner Parker is a rare exception. It's a classic Sallen-Key filter hacked up with biased diodes as controlled resistors.
==== Wasp ====
The Wasp filter is a State Variable with 4069 inverters replacing the inverting opamp in the integrators. Certainly the overdrive characteristics of the 4069 inverter are different than an opamp, but it's in a local feedback loop, and in a global feedback loop, and I think the OTA overdrive will predominate anyway.
==== EMS diode ladder ====
The [[EMS diode ladder filter]] is the same as the Roland diode ladder, and they're both Moog Ladder knockoffs, knocked off sufficiently to get around the patent.
==== Arp 2600 ====
The original [[ARP 2600 filter]] is a clone of the Moog Ladder. The later ARP2600 filter has the same filter topology, but implemented inelegantly to get around the patent.
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Saitama, JAPAN.
{{reflist}}
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