[sdiy] Gain staging in 4-pole VCFs

[Rutger Vlek]

I'd be interested to hear (or rather read)!

Rutger


On 9 nov 2018, at 01:15, David G Dixon wrote:

> I do gain staging in the Dr Octature 4-pole filter.  I'll explain it in
> detail later when I'm not in a hurry to leave work.  It was one of my
> cleverer moments.
> 
> 
>> -----Original Message-----
>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
>> Behalf Of Rutger Vlek
>> Sent: Thursday, November 08, 2018 12:07 PM
>> To: Synth DIY
>> Subject: [sdiy] Gain staging in 4-pole VCFs
>> 
>> Hi list,
>> 
>> I just remembered something I read years ago on the Oakley 
>> sound website regarding gain staging inside filters (usually 
>> those with >2 poles). It was regarding the COTA filter 
>> (cascaded OTA), where Tony only briefly explains using 
>> integrators with varying amounts of gain throughout the 
>> filter. Hereby (I presume) generating a very smooth combined 
>> saturation curve, where each stage contributes its share 
>> (much like guitar distortion pedals with several stages of 
>> saturation involved). He refers to a famous filter that 
>> inspired him for doing this, and I'm curious which one (the 
>> design choice sounds like one Dave Rossum would make...). 
>> Also, I'm curious which other filters use this approach.
>> 
>> I'd be interested if anyone can contribute with knowledge 
>> about specific filters and their gain staging, And perhaps 
>> Tony, would you be willing to shed some more light on this?
>> 
>> Some years ago I design the filter that's now on the market 
>> as Dendrites, in which I tried to model (in analog) different 
>> resonance responses of filters I knew. Its gain staging (and 
>> therefore saturation characteristic) is fixed though, and at 
>> unity for each stage. I'd be interested to see if I could 
>> take this modeling approach a step further, perhaps with 
>> different saturation elements (diff-pair transistors, diodes) 
>> or with different gain staging.
>> 
>> Regards,
>> 
>> Rutger
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>