FW: Parametric EQ Schem

[JOHN VOLANSKI]

Gene wrote:
 ----------
From:  gstopp[SMTP:gstopp at fibermux.com]
Sent:  Thursday, March 06, 1997 2:37 PM
To:  synth-diy
Subject:  Re: Parametric EQ Schem

      One problem with building manually-tuneable state-variable filters   
is
     that you need to use dual pots for the frequency controls. One way
     around this is to use OTA's and tune them with a single CV. If you   
did
     that you'd have a voltage-controlled parametric EQ and you'll be
     tempted to add all kinds of CV inputs (sweep, spread, etc.) so   
beware.
       

     One other thing to note would be that each state-variable bandpass
     filter will have a non-controllable bandwidth (well it is affected   
by
     Q, but that's another complication). In order to have mid-bands with   

     frequency *and* bandwidth adjustments, you'd need to make the band   
out
     of a pair of filters in series, one highpass and one lowpass, and as   

     you can see the number of parts in this design is getting up there.
       

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This sounds cool, and it kinda reminds me of the VCF travelers on the   
Korg 770 I used to have.  That mono synth had a low pass slider and a   
high pass slider on the VCF right next to each other.  You could set them   
to get some neat effects, such as a bandpass or notch that was sweepable   
with CV.  You could grab both sliders and move them together, so that in   
effect, you were sliding the notch or bandpass "Q" up and down the freq   
spectrum.  Ya know, I shoulda kept that synth......(the age-old lament).

JV