[sdiy] vco-vcf CV tracking

[Gavin Russom]

This is Tom G's OB type state variable filter that we were talking so much
about a month ago.  What value trimmers are suitable as 1v/oct trimmers, and
is it possible to add temp compensation as an afterthought on the filter
board? or will I need to re do the board :( ?
thanks as always
G.
----------
>From: harry bissell <paia2720 at yahoo.com>
>To: Gavin Russom <elmystico at earthlink.net>, synth <synth-diy at dropmix.xs4all.nl>
>Subject: Re: [sdiy] vco-vcf CV tracking
>Date: Fri, Jan 4, 2002, 4:49 PM
>

>What filter are you using ?
>
>Some filters are not designed to be accurate over
>a wide range of CV... some work very well !
>
>Temperature compensation of the filter expo converter
>is almost always used / needed in designs that track
>over a wide range.  If it is not compensated, its
>probably not expected to track very well.
>
>Trimming for 1V/oct is needed to get accuracy. If the
>design does not include this, again... its probably
>not expected to track well.
>
>Our hearing is not super accurate for changes in tone
>color (timbre) as it is for pitch. You can tolerate
>a sloppy filter cutoff WAY more than an oscillator
>that
>is even a tiny bit out of tune !
>
>H^) harry
>
>
>
>
>--- Gavin Russom <elmystico at earthlink.net> wrote:
>> Okay, 
>> If I am using a patch where the same CV is
>> controlling a VCO and the VCF
>> that is filtering it, then I should get this result:
>>  as the CV changes I
>> would hear the pitch change but each pitch would be
>> filtered in the same
>> way, if filter cuttoff was selected to produce a
>> hollow reedy sound then
>> each pitch would have a hollow reedy sound, right?
>> What shouldn't happen is that the changing pitch
>> goes in and out of
>> audibility because it is being filtered in different
>> ways, right?
>> Standard modular procedure is to use 100k input
>> impedence, which was
>> followed in this case, but when I use a sequencer to
>> control my homebuilt
>> VCO and VCF in this manner, they do not track
>> properly.  What would need to
>> be adjusted in this case?  Perhaps a trim pot for
>> the 1V/oct inputs? 
>> Temperature compensation?
>> Glad to hear all ideas
>> Thanks again
>> Gavin
>> 
>> 
>
>
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