[sdiy] tanh distortion in a filter

[Scott Nordlund]

> > Assuming work in the digital domain: Is tanh distortion something that works in a filter like a state variable? If so, where does the distortion go?
> 
> I seem to recall seeing a Dave Rossum paper on this, in some conference proceedings... alas, I can't remember more than that.
> 
> - Aaron

I think the Rossum paper is "Making Digital Filters Sound 'Analog'". He suggests clipping (or otherwise distorting) the delay path of a biquad, but not the input or output. It's a pretty dated paper, from 1992, so it's probably not something to rely on unless you're just looking to do something cheaply. Antti Huovilainen wrote the stuff about emulating the Moog transistor ladder filter by embedding tanh functions (derived from transistor differential pairs). I don't know how much of that would be applicable to state variable filters.