[sdiy] Linear VCF control

Harald sdiy at haraldswerk.de
Fri Nov 9 18:58:23 CET 2018


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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