Parametric EQ Schem

gstopp at gstopp at
Fri Mar 7 02:00:23 CET 1997

     The fuss about dual pots is that they are a little harder to find - 
     that's all. No real design problem.
     As far as using the Q pot to control the bandwidth, yes you can do 
     that, but it would be nice to a) have a change in bandwidth without a 
     change in resonant peak gain, and b) be able to set it wider than a 
     single state-variable bandpass output will allow. Like - what if you 
     want a passband that is 1000 Hz wide, etc. I understand that you can 
     reduce the resonance effect by reducing the input level as you 
     increase the Q, but in the opposite direction your bandwidth stops 
     increasing when Q reaches zero and you are stuck there.
     So - the question now becomes, how do you configure a state-variable 
     filter to provide cut/boost with a single pot rotation? I can tell 
     that I would need a few sheets of paper to figure this one out... plus 
     maybe some protoboard experiments...
     - Gene
     gstopp at

______________________________ Reply Separator _________________________________
Subject: Re: Parametric EQ Schem
Author:  Magnus Danielson <magda at> at ccrelayout
Date:    3/6/97 4:15 PM
Please tell me what the big fuzz about double pots is all about... I 
can imagine diffrencies between the pots, but what else?
Hello! Stop it rigth there...
I used a 2-pole standard state-variable filter and let the BP output 
be used for the summer, I could easilly vary the bandwidth using the 
so called Q-pot. The fact is that the Q value is the inverse of the 
bandwidth divided by the nominal centrum frequency...
The bandwidth is really set by the distance of the poles from the 
jomega axis in the s-plane map.
Please do... but leave a normal parametric design behind or I will 
have to do that ;-)

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