Hi All,
I'm a bit stumped and have been for years on how to leverage active filters into actual tone shaping controls. Lots of articles explain how to make a "filter" but spend less time on how to blend various filters in tone shaping or equalizers, so it's never been 100% clear to me. After reviewing some EQ schematics I see a lot of mixing amps and examples of the filters being put into feedback loops. I want to make a high shelf control for a treble boost that can be controlled for frequency and gain. I don't need cut, I don't need steep filters, I'm concerned about noise. What I've come up with is attached. It uses a first order state variable that is explained on this page:
State Variable Filters
in figure 1A. I'm using this filter (Varying R5 for frequency) and mixing it into a summing amp via R8. As R8 drops the boost increases but the taper seems weird and I can't get the boost to 0 without making R8 infinite, so I added the attenuator of R4 and R9; R8 now sets max gain. That attenuator would be the "boost" potentiometer.
Is this a reasonable approach for what I'm trying to do?
I'm a bit stumped and have been for years on how to leverage active filters into actual tone shaping controls. Lots of articles explain how to make a "filter" but spend less time on how to blend various filters in tone shaping or equalizers, so it's never been 100% clear to me. After reviewing some EQ schematics I see a lot of mixing amps and examples of the filters being put into feedback loops. I want to make a high shelf control for a treble boost that can be controlled for frequency and gain. I don't need cut, I don't need steep filters, I'm concerned about noise. What I've come up with is attached. It uses a first order state variable that is explained on this page:
State Variable Filters
in figure 1A. I'm using this filter (Varying R5 for frequency) and mixing it into a summing amp via R8. As R8 drops the boost increases but the taper seems weird and I can't get the boost to 0 without making R8 infinite, so I added the attenuator of R4 and R9; R8 now sets max gain. That attenuator would be the "boost" potentiometer.
Is this a reasonable approach for what I'm trying to do?
