[sdiy] Gain staging in 4-pole VCFs
rutgervlek at gmail.com
Fri Nov 9 09:49:29 CET 2018
I'd be interested to hear (or rather read)!
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.
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