[sdiy] Linear VCF control

Tom Bugs admin at bugbrand.co.uk
Fri Nov 9 18:01:27 CET 2018

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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