> Hi olli
>
> via http://matrixsynth.blogspot.com/2010/12/diy-digital-synth-demo.html
> I stumbled over http://www.national.com/mpf/MF/MF10.html#Overview
>
> Needs a clock instead of CV, but a simple VCO (no extreme linearity is
> required for this kind of VCF) shouldn't be too difficult.
>
> I think it would be also extremely useful as anti aliasing filter for
> the BBD modules.
>
> Florian

The main disadvantage of switched capacitor filters (SCF) is that you still
need an analog anti aliasing filter at the audio input and a tracking filter
(at least 12dB/oct) at the audio output to suppress the clock signal that is
used to control the SCF. This makes the design very complex as one needs a
high speed VCO that controls the clock of the SCF and two analog tracking
filters that have to follow the high speed VCO frequency. This is the reason
why our dual SCF has not yet been released. In this design 4 analog tracking
filters (all LM13700 based in our design) are necessary in addition to the
high speed VCO and the actual SCF. From my point of view it's too costly for
what you get. Ingo has tried out our prototype some time ago and as far as I
remember he agreed (Ingo please correct me if I'm wrong).

Best wishes
Dieter