Anderton MIF

[Grant Richter]

This is similar to the Richter Polymorphic Filter design now being marketed
as the Wiard Omni-Filter. The filter uses the individual filter "cells"
surrounded by solid state switches that rewire each of the four cells
into lowpass, highpass and allpass topologies. A bandpass mode is available
using two lowpass cells in series with two highpass cells.

The cells use FET buffered LM13700s.

An input thermometer circuit (using a 339 and 4070) is dithered
with a 44.1 Khz sawtooth wave so the switches move from 0-100% duty
cycle as the mode is advanced and intermediate modes are available
at the variable duty cycle points. 20 Khz 24 Db/octave guard filters on the
input and output prevent aliasing and reconstruct the chopped signal.

We have been shipping this filter since 1996.

My experience has been that full use of all four sections in series gives
the most noticeable results. The alternate responses described by putting
cells in parallel are easier to achieve using the Expander/Matrix 12 type
of "pole summing" as detailed on this web page.

http://www.musicsynthesizer.com/Multi-Function%20VCF.htm

----------
>From: John E Blacet <blacet at metro.net>
>To: synth-diy at node12b53.a2000.nl
>Subject: Re: Anderton MIF
>Date: Wed, Jun 28, 2000, 2:45 AM
>

> ..."an ultrasonic dither triangle on the CV, you could make
> a scanning linear interpolator like this too ;-)"
>
> Is this a plan to get rid of the "overlap" on the National BG chips?
> I simply burn to make something like a VC rotary switch thingy with one.
> My notebook has lots of doodles....
> --
>
> Regards.
> -------------------------
> John Blacet
> Blacet Research Music Electronics
> http://www.blacet.com
> -------------------------
> blacet at metro.net
> -------------------------
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