[sdiy] Linear VCF control

Quincas Moreira quincas at gmail.com
Fri Nov 9 19:31:33 CET 2018


Matthew Skala (North Coast Modular) has designed the Leapfrog Filter, which
does indeed have Lin FM, as well as Expo.
https://youtu.be/akMwn7jVV6A

On Fri, Nov 9, 2018 at 11:59 AM Harald <sdiy at haraldswerk.de> wrote:

> It is quite easy to add linear control to a OTA based VCF. I have done
> on most of my DIY filters. Example here:
> https://www.haraldswerk.de/NGF_E/NGF_E_24dB_LP_HP/NGF_E_24dB_LP_HP.html
>
> Am 09.11.18 um 18:01 schrieb Tom Bugs:
> > I think a few have cropped up recently in Euro (but I can't think of
> names)
> > If the VCF is based around an OTA then it is often fairly easy to add
> linear to
> > the usual sort of matched-pair exponential converter - not sure how
> that'd help
> > with temperature compensation though.
> > Somehow I don't think I ever actually tried it though.
> >
> >
> > On 09/11/2018 16:53, Mattias Rickardsson wrote:
> >> Hi all,
> >>
> >> following the recent discussions about temperature compensation of
> >> exponentially VCFs, one could imagine that the easiest way of avoiding
> the
> >> temperature dependence would be to control the filter linearly (Hz/V)
> instead
> >> of exponentially. I can't remember seeing it done in a VCF, though.
> Even if
> >> there are VCOs with linear control in currently produced synths - the
> latest
> >> example might be the Moog One if I'm correctly informed.
> >>
> >> A quick search in the SDIY archives returned some hits in an
> interesting old
> >> thread called "Filter frequency cutoff with linear response?" from
> 2012, where
> >> Olivier Gillet, Florian Anwander and Tom Wiltshire pointed out that the
> >> CEM3394 has linear filter FM from the onboard VCO's triangle wave via
> an
> >> onboard modulation VCA. The datasheet of the CEM3394 describes it some
> more. I
> >> remember liking the filter FM in the Akai AX-60, and this was it. It
> still
> >> relies on exponential VCF in the regular filter CV input though.
> >>
> >> PAiA Fatman was mentioned as having linear control of both VCO and VCF.
> Any
> >> other pure Hz/V filters out there? Or do people consider it a genuinly
> bad
> >> idea (except for the lack of V/oct CV input and the need of increased
> CV
> >> resolution/precision in the lower frequency range)? The bonus
> possibilities of
> >> linear FM might make it worthwhile. :-)
> >>
> >> /mr
> >>
> >>
> >>
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-- 
Quincas Moreira
Synth Diy Guy
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