[sdiy] Craig Anderton's Multiple Identity Filter

[David G Dixon]

Yes, we were also going to do a morphing filter initially, but it just
didn't sound that amazing, so we decided to do something slightly simpler. 

> -----Original Message-----
> From: Olivier Gillet [mailto:ol.gillet at gmail.com] 
> Sent: Thursday, October 27, 2016 5:04 AM
> To: Tom Wiltshire
> Cc: David G Dixon; sdiy
> Subject: Re: [sdiy] Craig Anderton's Multiple Identity Filter
> 
> > I'm guessing you went this way. A 17-bit code gives you at 
> least 8 resistor options for each of 5 inputs to the mixer 
> (e.g. a 4051 for each one). Under uP control this gives 
> fantastic flexibility and the problem becomes finding 
> "useful" or "interesting" responses from a system which will 
> include many duplicates and things that just aren't that good 
> - including 30 from the 131,000+ possibilities suggests you 
> did the required serious pruning!
> 
> Pruning indeed! I prototyped a design in which each filter 
> stage goes into a an attenuverter whose gain is controlled by 
> a MCU. The goal was to allow continuous morphing from one 
> response to the other, with each stage's "coefficient" being 
> computed from 3 parameters: slope, response (LP to BP to HP) 
> and "polarity" (LP becomes HP, BP becomes notch, HP becomes 
> LP). And it's not that interesting, with many combinations of 
> parameters sounding mild. I think you get more flexibility, 
> for the same hardware budget, with two SVF with 
> LP/Notch/HP/BP crossfading, and crossfading between 
> serial/parallel routing.